Displays

     The last seventy years have witnessed a marked acceleration of the impact of human activity impacting the planet due to the combination of rapid population growth, increased consumption of resources, and technological development. Nearly the entire human population occupies an astonishingly small percentage of the Earth’s surface, yet the imprint of human activity is being recorded in global climate and is perturbing the chemistry and composition of the most remote stretches of the atmosphere. These remote regions are exceptionally important for global air quality and climate (accounting on average for 75% of global CH₄ removal, 59% of chemical production of O₃, and 68% of chemical destruction of O₃), yet the paucity of observations over the remote oceans have limited our understanding of these fundamental processes and their sensitivity to increased human perturbation.

     The NASA Atmospheric Tomography Mission (ATom) was designed to address these gaps in our understanding of chemical composition, reactivity, and transport through a combination of extensive measurements and photochemical modeling, and to provide much needed observational data from the remote regions of the atmosphere to provide rigorous tests that will lead to improvements in our global chemistry-climate models and to validate remote sensing retrievals. From 2016-2018, ATom utilized the fully instrumented NASA DC-8 research aircraft to collect an unprecedented suite of measurements of trace gases, aerosols, and key radical species from the remote troposphere and lower stratosphere.  Four complete pole-to-pole global circuits (one in each season) were conducted by performing near-continuous vertical profiles between 0.2 – 14 km altitude along meridional transects of the Pacific and Atlantic Ocean Basins. The data provided by this project have already led to several significant new findings, with many more on the horizon as research teams continue to uncover the full value of this dataset. In this talk, we will provide an overview of the ATom mission and discuss some of the major outcomes and new findings that have resulted from this project to date.

How to cite: Thompson, C. and the The ATom Science Team: The NASA Atmospheric Tomography Mission: A Global-Scale Survey of Composition, Reactivity, and Transport in the Remote Atmosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12202, https://doi.org/10.5194/egusphere-egu2020-12202, 2020.

Observations from the NASA Atmospheric Tomography Mission (ATom) have elucidated a strong relationship between the production of hydroxyl radical (OH), the primary oxidant of the troposphere, and formaldehyde (HCHO), a major product of the oxidation of methane and other hydrocarbons.  We present a proxy for global over-ocean OH based on this principle, using remote observations of HCHO from the Ozone Monitoring Instrument (OMI).  Analysis of summer and wintertime remote OH from this proxy suggest a near-constant mean concentration of 1.03 ± 0.25 × 10⁶ cm⁻³ and a Northern Hemisphere to Southern Hemisphere over-ocean OH ratio of 0.89 ± 0.06 averaged over both seasons (1s uncertainties).  We also share ongoing efforts to expand on this approach by refining the scaling factors that relate OH production to HCHO as a function of CO, NO_x, and VOCs, with the goal of extending the proxy over land as well as across the OMI record.

How to cite: Nicely, J., Wolfe, G., St. Clair, J., Hanisco, T., Liao, J., Oman, L., and González Abad, G. and the ATom Science Team: Mapping the Oxidizing Capacity of the Global Remote Troposphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12042, https://doi.org/10.5194/egusphere-egu2020-12042, 2020.

Reactive halogens have wide-ranging consequences on tropospheric chemistry including ozone destruction, HOx and NOx partitioning, oxidization of volatile organic compounds (VOCs) and initiation of new particle formation. Of particular note and importance, the tropospheric Ox loss due to halogens is estimated to be between 10-20% globally, and up to 50% in some local marine environments. In this work, we include a state-of-the-art coupled halogen and VOCs chemical mechanism into the CAM-Chem global model. Complementing the model development and providing the opportunity to test the model are recent results from the NASA Atmospheric Tomography (ATom) experiment.  ATom was conducted with a heavily instrumented NASA DC-8 aircraft over the course of two and a half years, transecting the lengths of the Pacific and Atlantic Oceans during four seasons, constantly profiling from the surface (200 m) to the upper troposphere/lower stratosphere (12000 m). The ATom payload included instruments that measured both inorganic halogens and organic halogen-containing very short-lived substances (VSLS), as well as those that measured additional volatile organic compounds (VOCs), including hydrocarbons and oxygenated VOCs (OVOCs), both of which react with halogens. Modeled BrO is sensitive to the inclusion of reactions between Br and OVOCs, particularly the aldehydes, which rapidly convert Br to HBr, a far less reactive form of Br_y. These reactions can have large implications in the remote troposphere where the ATom measurements have revealed significant emissions and chemical production of low molecular weight aldehydes over the remote marine environment. A version of CAM-chem, updated to include aldehyde emissions from the ocean to close the gap between models and measurements, is used in these analyses. Comparisons between measured and modeled halogen containing species, both organic and inorganic, is presented along with a summary of the implications of our findings on the overall budgets of tropospheric halogens and ozone.

How to cite: Apel, E. C.: Interactions and implications of halogens and VOCs on tropospheric oxidant cycles in the remote atmosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5877, https://doi.org/10.5194/egusphere-egu2020-5877, 2020.

Tropospheric ozone (O₃) can adversely affect human health and environmental ecosystems and it is therefore vitally important to understand its formation pathways from both natural and anthropogenic precursors. Background O₃ levels in the Northern Hemisphere have increased by more than a factor of two over the last century and it is believed that this increase is strongly tied to the increase in and distribution of anthropogenic nitrogen oxide (N0_x) emissions. This is important as the changing level of O₃ in the background troposphere impacts the ability of countries downwind to achieve their air quality standards.

As part of the NERC funded North Atlantic Climate System Integrated Study (ACSiS) and Methane Observations and Yearly Assessments (MOYA) projects, multiple research flights have taken place over the North Atlantic Ocean, spanning an area from 55^oN to 12^oN and 8^oW to 25^oW using the UK’s large research aircraft (The Facility for Airborne Atmospheric Measurements – FAAM). Flights took place in all seasons from 2017 – 2020. A variety of gas and aerosol measurements were made, including NO_x, O_3, CO and a range of VOCs and an overview of the data is presented here. Measurements were taken in a range of air masses, including biomass burning outflow from West Africa, urban outflow from Europe and emissions from the busy shipping lanes to the West of Portugal.

Data was analysed to assess O₃ formation from the different emission sources, in particular examining the difference between anthropogenic and natural emissions. In addition, the output of regional chemistry models is compared to the data in order to assess the performance of the models in predicting O₃ and its precursors.

How to cite: Lee, J., Squires, F., Andersen, S., Hopkins, J., Pasternak, D., and Archibald, A.: Measurement of NOx and Ozone over the North Atlantic Ocean., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8233, https://doi.org/10.5194/egusphere-egu2020-8233, 2020.

The UTLS (Upper Troposphere/Lower Stratosphere) is a key layer of the atmosphere as its chemical composition impacts both the troposphere and the stratosphere, and therefore plays a significant role in the climate system. Ozone at this altitude for instance plays a great role on surface temperature. Unlike in the stratosphere; it can be produced from the photolysis of precursors originating in the troposphere; mainly nitrous oxides (NO_x) and carbon monoxide (CO) at this pressure range. Biomass burning emissions in particular are likely to play a significant role in the quantities of these species in the upper troposphere and thus impacting ozone balance. This effect is investigated thanks to the global chemistry transport model MOCAGE. Because of the strong vertical gradients in this layer of the atmosphere, well resolved in-situ observation dataset are valuable for model evaluation. As of measurements used to validate MOCAGE results, IAGOS in-situ measurements from equipped commercial aircraft were chosen for their fine vertical resolution as well as their wide geographical coverage. Using both of these tools, upper tropospheric air composition is studied, with a focus on ozone precursors and production linked to biomass burning emissions.

Firstly is investigated the direct impact of biomass burning emissions on CO concentration in the upper troposphere, as it is both a good tracer of wildfire plumes in the atmosphere and it plays a role in the upper troposphere chemical balance. For this purpose MOCAGE simulations spaning over the year of 2013 where biomass burning emissions were turned on and off are compared to estimate a contribution to upper tropospheric CO. These simulations were validated using all the available data from the IAGOS database. It was found that biomass burning impacted CO levels globally, with the strongest enhancement happening above the most emitting areas (equatorial Africa and the Boreal forests). The importance of a fast vertical transport pathway above the fires was also highlighted with the possible occurrence of pyroconvection in addition to deep convection. Secondly, other chemical species related to ozone production were looked upon. Peroxyacetyl Nitrates (PAN) for instance were found to be impacted by biomass burning as it is a product of NOx oxidation as well as the main "reservoir" specie for NOx in the upper troposphere. Ultimately, ozone production resulting from biomass burning emissions is investigated, both in biomass burning plumes encountered by IAGOS aircraft, and on a more global scale using the MOCAGE simulations.

How to cite: Cussac, M., Marécal, V., Thouret, V., and Josse, B.: Analysis of the impact of biomass burning emissions on global ozone production in the upper troposphere with MOCAGE CTM and IAGOS airborne data., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5628, https://doi.org/10.5194/egusphere-egu2020-5628, 2020.

The European Centre for Medium-Range Weather Forecasts’ (ECMWF’s) next-generation reanalysis ERA5 provides many improvements, but it also confronts the community with a "big data" challenge. Data storage requirements for ERA5 increase by a factor of ∼80 compared with the ERA-Interim reanalysis, introduced a decade ago. Considering the significant increase in resources required for working with the new ERA5 data set, it is important to assess its impact on Lagrangian transport simulations. To quantify the differences between transport simulations using ERA5 and ERA-Interim data, we analyzed comprehensive global sets of 10-day forward trajectories for the free troposphere and the stratosphere for the year 2017. The new ERA5 data have a considerable impact on the simulations. Spatial transport deviations between ERA5 and ERA-Interim trajectories are up to an order of magnitude larger than those caused by parameterized diffusion and subgrid-scale wind fluctuations after 1 day and still up to a factor of 2–3 larger after 10 days. Depending on the height range, the spatial differences between the trajectories map into deviations as large as 3 K in temperature, 30 % in specific humidity, 1.8 % in potential temperature, and 50 % in potential vorticity after 1 day. Part of the differences between ERA5 and ERA-Interim is attributed to the better spatial and temporal resolution of the ERA5 reanalysis, which allows for a better representation of convective updrafts, gravity waves, tropical cyclones, and other meso- to synoptic-scale features of the atmosphere. Another important finding is that ERA5 trajectories exhibit significantly improved conservation of potential temperature in the stratosphere, pointing to an improved consistency of ECMWF’s forecast model and observations that leads to smaller data assimilation increments. We conducted a number of downsampling experiments with the ERA5 data, in which we reduced the numbers of meteorological time steps, vertical levels, and horizontal grid points. Significant differences remain present in the transport simulations, if we downsample the ERA5 data to a resolution similar to ERA-Interim. This points to substantial changes of the forecast model, observations, and assimilation system of ERA5 in addition to improved resolution. A comparison of two Lagrangian trajectory models allowed us to assess the readiness of the codes and workflows to handle the comprehensive ERA5 data and to demonstrate the consistency of the simulation results. Our results will help to guide future Lagrangian transport studies attempting to navigate the increased computational complexity and leverage the considerable benefits and improvements of ECMWF’s new ERA5 data set.

Reference: Hoffmann, L., Günther, G., Li, D., Stein, O., Wu, X., Griessbach, S., Heng, Y., Konopka, P., Müller, R., Vogel, B., and Wright, J. S.: From ERA-Interim to ERA5: the considerable impact of ECMWF's next-generation reanalysis on Lagrangian transport simulations, Atmos. Chem. Phys., 19, 3097–3124, https://doi.org/10.5194/acp-19-3097-2019, 2019.

How to cite: Hoffmann, L., Günther, G., Li, D., Stein, O., Wu, X., Griessbach, S., Heng, Y., Konopka, P., Müller, R., Vogel, B., and Wright, J. S.: From ERA-Interim to ERA5: considerable impact of ECMWF's next-generation reanalysis on Lagrangian transport simulations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1919, https://doi.org/10.5194/egusphere-egu2020-1919, 2020.

Climate change is one of the biggest challenges of the modern era. Halocarbons contribute already about 14% to current anthropogenic radiative forcing, and their future impact may become significantly larger due to their long atmospheric lifetimes and continued and increasing usage. In addition to their influence on climate change, chlorine and bromine-containing halocarbons are the main drivers of the destruction of the stratospheric ozone layer. Therefore, observing their atmospheric abundance and quantifying their sources is critical for predicting the related future impact on climate change and on the recovery of the stratospheric ozone layer.

Regional scale atmospheric inverse modelling can provide observation-based estimates of greenhouse gas emissions at a country scale and, hence, makes valuable information available to policy makers when reviewing emission mitigation strategies and confirming the countries' pledges for emission reduction. Considering that inverse modelling relies on accurate atmospheric transport modelling any advances to the latter are of key importance. The main objective of this work is to characterize and improve the Lagrangian particle dispersion model (LPDM) FLEXPART-COSMO at kilometer-scale resolution and to provide estimates of Swiss halocarbon emissions by integrating newly available halocarbon observations from the Swiss Plateau at the Beromünster tall tower. The transport model is offline coupled with the regional numerical weather prediction model (NWP) COSMO. Previous inverse modelling results for Swiss greenhouse gases are based on a model resolution of 7 km x 7 km. Here, we utilize higher resolution (1 km x 1 km) operational COSMO analysis fields to drive FLEXPART and compare these to the previous results.

The higher resolution simulations exhibit increased three-dimensional dispersion, leading to a general underestimation of observed tracer concentration at the receptor location and when compared to the coarse model results. The concentration discrepancies due to dispersion between the two model versions cannot be explained by the parameters utilized in FLEPXART’s turbulence parameterization, (Obhukov length, surface momentum and heat fluxes, atmospheric boundary layer heights, and horizontal and vertical wind speeds), since a direct comparison of these parameters between the different model versions showed no significant differences. The latter suggests that the dispersion differences may originate from a duplication of turbulent transport, on the one hand, covered by the high resolution grid of the Eulerian model and, on the other hand, diagnosed by FLEXPART's turbulence scheme. In an attempt to reconcile FLEXPART-COSMO’s turbulence scheme at high resolution, we introduced additional scaling parameters based on analysis of simulated mole fraction deviations depending on stability regime. In addition, we used FLEXPART-COSMO source sensitivities in a Bayesian inversion to obtain optimized emission estimates. Inversions for both the high and low resolution models were carried out in order to quantify the impact of model resolution on posterior emissions and estimate about the uncertainties of these emissions.  

How to cite: Katharopoulos, I., Rust, D., Vollmer, M., Brunner, D., Reimann, S., Emmenegger, L., and Henne, S.: The influence of transport model resolution on the inverse modelling of synthetic greenhouse gas emissions in Switzerland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5159, https://doi.org/10.5194/egusphere-egu2020-5159, 2020.

Cirrus clouds are an important contributor to the uncertainty of future climate prediction, especially due to the weak understanding of anthropogenic impacts on cirrus clouds.

We investigate aerosol and cloud microphysical properties of the remote atmosphere over the Pacific and Atlantic Oceans from about 80°N to 86°S and the region in the Mediterranean using airborne aerosol and cloud measurements of the entire atmospheric column up to approx. 13 km from the ATom (Atmospheric Tomography; 2016-2018) and the A-LIFE (Absorbing aerosol layers in a changing climate: aging, lifetime and dynamics; 2017) field experiments, respectively. Aerosol microphysical properties are retrieved from in-situ measurements of aerosol particle size distributions between 0.003 and 50 µm, single particle mass spectrometry as well as simulations with the Lagrangian transport and dispersion model FLEXPART. The microphysical properties of cirrus clouds are obtained from size distribution measurements covering the range between 3 and 930 µm.

In this study we show microphysical properties of aerosols and cirrus clouds in regions with high mineral dust concentrations as well as pristine and anthropogenic influenced regions in order to advance the knowledge of the natural and anthropogenic impact on cirrus clouds.  We present comparisons of ice crystal number concentrations, aerosol and cloud particle size distributions, and meteorological conditions of cirrus clouds in the above-mentioned regions of the atmosphere.

How to cite: Dollner, M., Gasteiger, J., Brock, C. A., Schöberl, M., Williamson, C., Kupc, A., Philipp, A., Seibert, P., Froyd, K., Schill, G. P., Murphy, D. M., Diskin, G., Bui, T. P., and Weinzierl, B.: Comparison of cirrus clouds in naturally and anthropogenically influenced regions of the atmosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16472, https://doi.org/10.5194/egusphere-egu2020-16472, 2020.

Global climate model (GCM) ensembles still produce a significant spread of estimates for the future of climate change which hinders our ability to influence policymakers. The range of these estimates can only partly be explained by structural differences and varying choice of parameterisation schemes between GCMs. GCM representation of cloud and aerosol processes, more specifically aerosol microphysical properties, remain a key source of uncertainty contributing to the wide spread of climate change estimates. The radiative effect of aerosol is directly linked to the microphysical properties and these are in turn controlled by aerosol source and sink processes during transport as well as meteorological conditions.

A Lagrangian, trajectory-based GCM evaluation framework, using spatially and temporally collocated aerosol diagnostics, has been applied to over a dozen GCMs via the AeroCom initiative. This framework is designed to isolate the source and sink processes that occur during the aerosol life cycle in order to improve the understanding of the impact of these processes on the simulated aerosol burden. Measurement station observations linked to reanalysis trajectories are then used to evaluate each GCM with respect to a quasi-observational standard to assess GCM skill. The AeroCom trajectory experiment specifies strict guidelines for modelling groups; all simulations have wind fields nudged to ERA-Interim reanalysis and all simulations use emissions from the same inventories. This ensures that the discrepancies between GCM parameterisations are emphasised and differences due to large scale transport patterns, emissions and other external factors are minimised.

Preliminary results from the AeroCom trajectory experiment will be presented and discussed, some of which are summarised now. A comparison of GCM aerosol particle number size distributions against observations made by measurement stations in different environments will be shown, highlighting the difficulties that GCMs have at reproducing observed aerosol concentrations across all size ranges in pristine environments. The impact of precipitation during transport on aerosol microphysical properties in each GCM will be shown and the implications this has on resulting aerosol forcing estimates will be discussed. Results demonstrating the trajectory collocation framework will highlight its ability to give more accurate estimates of the key aerosol sources in GCMs and the importance of these sources in influencing modelled aerosol-cloud effects. In summary, it will be shown that this analysis approach enables us to better understand the drivers behind inter-model and model-observation discrepancies.

How to cite: Kim, P., Partridge, D., and Haywood, J.: Constraining the model representation of the aerosol life cycle in relation to sources and sinks., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21948, https://doi.org/10.5194/egusphere-egu2020-21948, 2020.

In the event of an accidental airborne release of radioactive material, dispersion models would be used to simulate the spread of the pollutant in the atmosphere and its subsequent deposition. Typically, meteorological information is provided to dispersion models from numerical weather prediction (NWP) models. As these NWP models have increased in resolution their ability to resolve short-lived, heavy precipitation events covering smaller areas has improved. This has led to more realistic looking precipitation forecasts. However, when traditional statistics comparing precipitation predictions to measurements at a point (e.g. an observation site) are used, these high-resolution models appear to have a lower skill in predicting precipitation due to small differences in the location and timing of the precipitation with respect to the observations. This positional error is carried through to the dispersion model resulting in predictions of high deposits where none are observed and vice versa; a problem known as the double penalty problem in meteorology.

Since observations are not available at the onset of an event, it is crucial to gain insight into the possible location and timing errors. One method to address this issue is to use ensemble meteorological data as input to the dispersion model. Meteorological ensembles are typically generated by running multiple model integrations where each model integration starts from a perturbed initial state and uses slightly different model parametrisations to represent uncertainty in the atmospheric state and its evolution. Ensemble meteorological data provide several possible predictions of the precipitation that are all considered to be equally likely and this allows the dispersion model to produce several possible predictions of the deposits of radioactive material.

As part of the Euratom funded project, CONFIDENCE, a case study involving the passage of a warm front, where the timing of the front is uncertain in relation to a hypothetical nuclear accident in Europe was examined. In this study a ten-member meteorological ensemble was generated using time lagged forecasts to simulate perturbations in the initial state and two different model parameterisations. This meteorological ensemble was used as input to a single dispersion model to generate a dispersion model ensemble. The resulting ensemble dispersion output and methods to communicate the uncertainty in the deposition and the resulting uncertainty in the air concentration predictions are presented. The results demonstrate how high-resolution meteorological ensembles can be combined with dispersion models to simulate the maximum impact of precipitation and the uncertainty in its position and timing.

How to cite: Leadbetter, S., Bedwell, P., Geertsema, G., Korsakissok, I., Tomas, J., de Vries, H., and Wellings, J.: Take one dispersing plume and add some precipitation: using ensembles to simulate deposition uncertainty, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7132, https://doi.org/10.5194/egusphere-egu2020-7132, 2020.

When scientific or policy-relevant questions involve atmospheric chemistry, one often hears "nonlinear" being invoked to describe the problem in a vague unspecific way.  The precise nature of the nonlinearity is never delineated, and we are left with the fuzzy impression that nonlinear problems are difficult to solve or have no simple answer.  For differentiable systems, nonlinear behavior can be expressed through a Taylor expansion whereby any of the 2^nd order terms (x², y² or xy) are the first nonlinear parts.  In this lecture we shall explore a range of scientific discoveries or developments in atmospheric chemistry where the nonlinear nature was critical to understanding the problem.  I select a set of problems worked on by many colleagues and myself over the last four decades.  These include:  multiple solutions in stratospheric chemistry; depletion of ozone; numerical methods for tracer transport; our developing understanding of methane; chemical feedbacks and indirect greenhouse gases; and finally the rich heterogeneity of gases that drives tropospheric chemistry. I hope to convince you that by embracing the nonlinear nature of atmospheric chemistry and understanding when it is important and when it is not, we can advance the field.   

How to cite: Prather, M.: The Nonlinear Nature of Atmospheric Chemistry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22479, https://doi.org/10.5194/egusphere-egu2020-22479, 2020.

The NASA Atmospheric Tomography Mission (ATom) aimed to improve the understanding of atmospheric composition through global scale aircraft sampling campaigns in different seasons. The flights included continuous profiling between 0.2 and 12 km over the Atlantic and Pacific Oceans.

A large number of samples were taken using the Whole Air sampler (WAS, UC Irvine, CA). In a selection of these samples, we measured the stable isotopic composition of CO, H₂ and CH₄. The samples cover remote clean air from different latitudes, from troposphere and lower stratosphere, and air influenced by specific (pollution) sources or processes.

We will give an overview of the data available and the main characteristics. We observe large variations in the isotopic composition, showing the large scale influence of tropospheric sources and sinks, but also stratospheric processing. The three gas species are mainly affected by the same sources and processes but in different ways, thus giving complementary information on the atmospheric processes.

How to cite: Popa, M. E., van der Veen, C., Meinardi, S., Blake, D. R., and Roeckmann, T.: Stable isotopic composition of CO, H2 and CH4 in the troposphere and lower stratosphere: results from the ATom-WAS samples, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11517, https://doi.org/10.5194/egusphere-egu2020-11517, 2020.

Current estimates suggest that globally, about one third of low-level cloud condensation nuclei (CCN) originate from new particle formation (NPF) in the free troposphere. However, the exact mechanisms of how these new particles form and grow to CCN sizes are not yet well quantified. We investigate the formation of new particles and their initial growth in the remote marine atmosphere over the Pacific and Atlantic basins (~80 °N to ~86 °S using (1) gas-phase and size distribution measurements (0.003-4.8 µm) from the airborne-based NASA Atmospheric Tomography global survey (ATom; 2016-2018), (2) back trajectory data, and (3) two aerosol microphysics box models.

In the ATom observations, newly formed particles were ubiquitous at high altitudes throughout broad regions of the tropics and subtropics under low condensation sink conditions and were associated with upwelling in convective clouds. This pattern was observed over four seasons and both ocean basins.

In this study, we explore processes that govern NPF and growth in the tropical and subtropical free troposphere, discuss similarities and differences in NPF over both ocean basins, use box models to examine which nucleation schemes (e.g. binary, ternary, or charged) best explain the observations, and evaluate whether sulfuric acid precursors alone can explain the NPF and the initial particle growth. Comparing aerosol size distribution measurements with box model simulations shows that none of the NPF schemes commonly used in global models are consistent with observations, regardless of precursor concentrations. Newer schemes that incorporate organic compounds as nucleating or growth agents can plausibly replicate the observed size distributions. We conclude that organic precursor species may be particularly important in NPF in the tropical upper troposphere, even above marine regions.

How to cite: Kupc, A., Williamson, C., Hodshire, A. L., Pierce, J. R., Kazil, J., Ray, E., Froyd, K., Rollins, A., Richardson, M., Weinzierl, B., Dollner, M., Erdesz, F., Bui, T. P., and Brock, C. A.: Using ATom observations and models to understand what precursors drive NPF in the remote free troposphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13313, https://doi.org/10.5194/egusphere-egu2020-13313, 2020.

Particulate matter is of special interest in atmospheric studies because it has important effects on both the Earth's climate and on human health.  Currently, aerosols contribute largest to the overall uncertainty of the net radiative effects in studies of climate change.  At the same time, aerosols are responsible for a large fraction of the overall impact of air quality on human health.  Mineral dust is an important aerosol constituent and makes up a significant part of the total aerosol load.  After its emission, mineral dust can be transported over very large distances in the atmosphere, and in extreme cases influence air quality far away from its source region.

The project Effect of Megacities on the Transport and Transformation of Pollutants on the Regional to Global Scales (EMeRGe) consisted of two measurement campaigns with the research aircraft HALO.  HALO operated for two four-week periods in Europe (based close to Munich) and East Asia (based in Taiwan) in July 2017 and March 2018, respectively.  The aircraft was fully equipped with extensive measurement instrumentation to sample atmospheric composition with a focus on the air pollution outflow from major population centers.

Here, we present simulations of coarse-mode aerosol transport to the East China Sea, where EMeRGe-Asia flight E_AS_F#11 was flying from Taiwan to Japan and back on 30 Mar 2018.  During the flight, enhanced concentrations of aerosol in the 0.5-3µm diameter range were measured using an optical particle counter (OPC) in several different locations.  We used version 10.4 of the FLEXPART Lagrangian dispersion model to simulate sensitivity fields to emissions of dust, sea-sealt, and biomass burning aerosol.  Combined with emission data for the three aerosol species, we can estimate the contribution of the different species and source regions to the measured aerosol enhancements.

Among others, our simulations show that mineral dust from as far as the Sahara desert in North Africa can contribute significantly to the total aerosol concentration over the East China Sea.

How to cite: Hilboll, A., Kalisz Hedegaard, A. B., Adam, L., Kaiser, K., Schneider, J., and Vrekoussis, M.: Simulation of mineral dust transport to the East China Sea with FLEXPART 10.4, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15855, https://doi.org/10.5194/egusphere-egu2020-15855, 2020.

Following its release and corresponding publication in GMD, we present the Lagrangian model FLEXPART 10.4, which simulates the transport, diffusion, dry and wet deposition, radioactive decay and first order chemical reactions of atmospheric tracers. The model has been recently updated, both technical and in the representation of physico-chemical processes. 

FLEXPART was in its original version in the mid-1990s designed for calculating the long-range and mesoscale dispersion of hazardous substances from point sources, such as released after an accident in a nuclear power plant. Given suitable meteorological input data, it can be used for scales from dozens of meters to the global scale. In particular, inverse modelling based on source-receptor relationships from FLEXPART has become widely used. In this paper, we present FLEXPART version 10.4, which works with meteorological input data from the European Centre for Medium-Range Weather Forecasts’ (ECMWF) Integrated Forecast System (IFS), and data from the United States’ National Centers of Environmental Prediction (NCEP) Global Forecast System (GFS). Since the last publication of a detailed FLEXPART description (version 6.2), the model has been improved in different aspects such as performance, physico-chemical parametrizations, input/output formats and available pre- and post-processing software. The model code has also been parallelized using the Message Passing Interface (MPI). We demonstrate that the model scales well up to using 256 processors, with a parallel efficiency greater than 75% for up to 64 processes on multiple nodes in runs with very large numbers of particles. The deviation from 100% efficiency is almost entirely due to remaining non-parallelized parts of the code, suggesting large potential for further speed-up. A new turbulence scheme for the convective boundary layer has been developed that considers the skewness in the vertical velocity distribution (updrafts and downdrafts) and vertical gradients in air density. FLEXPART is the only model available considering both effects, making it highly accurate for small-scale applications, e.g. to quantify dispersion in the vicinity of a point source. The wet deposition scheme for aerosols has been completely rewritten and a new, more detailed gravitational settling parameterization for aerosols has also been implemented. FLEXPART has had the option for running backward in time from atmospheric concentrations at receptor locations for many years, but this has now been extended to work also for deposition values . To our knowledge, to date FLEXPART is the only model with that capability. Furthermore, temporal variation and temperature dependence of chemical reactions with the OH radical have been included, allowing more accurate simulations for species with intermediate lifetimes against the reaction with OH, such as ethane. Finally, user settings can now be specified in a more flexible namelist format, and output files can be produced in NetCDF format instead of FLEXPART’s customary binary format. In this paper, we describe these new developments. Moreover, we present some  tools for the preparation of the meteorological input data and for processing of FLEXPART output data and briefly report on alternative FLEXPART versions. 

How to cite: Pisso, I. and the The FLEXPART developers: The Lagrangian particle dispersion model FLEXPART version 10.4, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22672, https://doi.org/10.5194/egusphere-egu2020-22672, 2020.

We analyze the long-range transport to high latitudes of a smoke particle filament originating from the southern tropics main plume after the Australian wildfires now colloquially known as ‘Black Saturday’ on February 7^th 2009. Using a high-resolution transport/microphysical model, we show that the monitoring cloud/aerosol lidar instrument operating at the French Antarctic station Dumont d’Urville (DDU - 66°S - 140°E) recorded a signature of those aerosols. The 532 nm scattering ratio of this thin aerosol structure is comparable to typical moderate stratospheric volcanic plume, with values between 1.4 and 1.6 on the 1^st and 3^rd days of March above DDU station at around the 14 and 16 km altitude respectively.

In this study, a dedicated model is described and its ability to track down such fine optical signatures at the global scale is assessed and validated against the Antarctic lidar measurements. Using one month of tropical CALIOP/CALIPSO data as a minimal support to a relatively simple microphysical scheme, we report modeled presence of the aerosols above DDU station after advection of the aerosol size distribution. The space-borne lidar data provide constraints to the microphysical evolution during the simulation and ensure reliable long-range transport of the particles as well as accurate rendering of the plume small-scale features below the 1°x1° resolution threshold.

This case study of smoke particle signature identification above Antarctica provides strong evidence that biomass burning events, alongside volcanic eruptions, have to be considered as processes able to inject significant amounts of material up to stratospheric altitudes. Among the questions arising out of this study, we highlight the occurrence and imprint of such smoke particles on the Antarctic atmosphere over larger time scales. Any degree of underestimation of the global impact of such deep particle transport will lead to uncertainties in modeling the associated chemical or radiative effects, especially in polar regions where many specific microphysical processes take place. Mainly through sedimentation, particle trapping above Antarctica may also impact the ground albedo (which is some of the largest in the world). Correlated to the smoke presence, we also report an associated ozone increase observed with the DDU ozone lidar. This feature only rarely been observed for events where pyroconvection is originally involved.

How to cite: Jumelet, J., Tencé, F., Keckhut, P., and Bekki, S.: Detection of aerosols in Antarctica from long-range transport of the 2009 Australian wildfires, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18222, https://doi.org/10.5194/egusphere-egu2020-18222, 2020.

Haze pollution caused by atmospheric aerosols has become one of the most severe environmental problems in China, especially in the Beijing-Tianjin-Hebei (BTH) region. Air pollution is not caused by local emission and secondary formation of air pollutants, but also affected by transport from its surrounding areas. A number of studies with respect to the regional transport of air pollutants in the BTH region have been conducted based on surface observation. However, owing to the inhomogeneous vertical distribution of air pollutants and meteorological conditions, the vertical profiles of transport fluxes should be considered for a comprehensive understanding of regional transport. In this study, the vertical profiles of aerosol and its precursor indicators HCHO, NO₂ and SO₂ were observed by ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) at the Nancheng (NC) site in suburban Beijing on the southwest transport pathway. The profiles of the pollutants varied with seasons with more aerosols concentrated at the surface in the winter. Through potential source contribution function (PSCF) analysis, southwest transport pathway was determined as the main transport source region, particularly for air pollutants in the middle and upper boundary layer. The transport fluxes of air pollutants at each vertical layer on the southwest-northeast direction were estimated combining with wind field simulated by WRF-Chem modeling. The average fluxes of the measured pollutants from June 2018 to May 2019 during the southwest transport (from southwest to northeast) were all higher than those during the northeast transport (from northeast to southwest), indicating net input of pollutants to urban Beijing from southwest transport pathway. Except for northwest transport of aerosols, the other maximum transport fluxes occurred at high altitudes instead of at the surface. The proportions of surface flux in the column flux for all the species during southwest transport were higher than those during northeast transport. Surface observation would overestimate the relative contribution from urban Beijing to southwest pathway and underestimate the contribution from southwest pathway to urban Beijing. Southwest transport played an important role on the developing stage of aerosol pollution in urban Beijing in the autumn and winter, and this transport mainly occurred in the middle boundary layer.

How to cite: Hu, Q., Liu, C., Ji, X., Liu, T., and Zhu, Y.: Vertical structure of the transport fluxes of aerosol and its precursors on the southwest transport pathway in the Beijing-Tianjin-Hebei region, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4967, https://doi.org/10.5194/egusphere-egu2020-4967, 2020.

Mesoscale meteorological phenomena, such as sea-land breeze regime, strongly impact meteorological conditions of coastal areas, affecting wind intensity, moisture, heat and momentum fluxes and polluted air masses dispersion. This effect must be considered in order to correct design urban spaces, predict the possible influence of land use change on air pollution and climate change and, consequently, improve the quality of life and urban comfort.

In recent years, it has been shown that the breeze regime does not only affect microclimatic conditions but also air quality in coastal areas, because of the mixing of different types of aerosols and condensable gases. Moreover, the advection of marine, colder and more humid air leads to the decrease of the boundary layer height and, consequently, to the increase of the surface concentration of locally emitted pollutants, that are trapped within the boundary layer itself.

The effect of breeze regime is particularly interesting in coastal cities, where the sea breeze entails large modification of physical, optical, chemical, and hygroscopic properties of the urban aerosol.

In this work, we developed an approach to determine the breeze effect on aerosol in correspondence of the BAQUNIN [1] Super-site urban location, in the centre of Rome, Italy. The city is about 28 km far from the Tyrrhenian coast and is often exposed to sea-breeze circulation and to extreme aerosol events [2] [3].

In-situ measurements obtained from different remote sensing instruments are used: (i) vertical profile of horizontal wind velocity and direction by means of SODAR wind profiler; (ii) moisture, air temperature and wind speed from ground-based meteorological station; (iii) aerosol optical depth (AOD), height and evolution of the Boundary Layer from Raman and elastic LIDAR; (iv) precipitable water, AOD, Ångström exponent (AE) and single-scattering albedo (SSA) from sun-photometer CIMEL [4], (v) AOD, AE and SSA from POM 01 L Prede sun-sky radiometer [5][6], (vi) superficial NO₂ and formaldehyde amounts from PANDORA spectrometer [7], (vii) particulate matter (PM_2.5 and PM₁₀) concentrations from ground-based air quality station.

The investigation is focused on several days, during summer of 2019, characterized by anemological breeze regime conditions.

In this study, we present preliminary results aimed to the in-depth analysis of the effects of the breeze regime on the optical properties of aerosols in coastal, urban environment and the impact of the aerosol vertical stratification on ground-level PM concentrations.

References:

[1] BAQUNIN Boundary-layer Air Quality-analysis Using Network of Instruments, www.baqunin.eu

[2] Petenko I. et al. (2011) “Local circulation diurnal patterns and their relationship with large-scale flows in a coastal area of the Tyrrhenian sea”, Boundary-Layer Meteorology, 139:353-366.

[3] Ciardini V. et al. (2012) “Seasonal variability of tropospheric aerosols in Rome”, Atmospheric Research, 118:205-214.

[4] AERONET, https://aeronet.gsfc.nasa.gov/new_web/index.html

[5] EUROSKYRAD http://www.euroskyrad.net/

[6] Campanelli M. et al. (2019) “Aerosol optical characteristics in the urban area of Rome, Italy, and their impact on the UV index”, Atmospheric Measurement Techniques Discussion.

[7] PGN, https://www.pandonia-global-network.org/

How to cite: Di Bernardino, A., Iannarelli, A. M., Casadio, S., Mevi, G., Campanelli, M., Casasanta, G., Cede, A., Tiefengraber, M., and Cacciani, M.: Effect of sea breeze regime on aerosol optical properties over the city of Rome, Italy., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9065, https://doi.org/10.5194/egusphere-egu2020-9065, 2020.

Abstract Text
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We developed an algorithm, for the first time, to retrieve nitrogen dioxide (NO2) vertical profile (surface NO2 volume mixing ratio) using multi NO2 slant column densities (SCDs) at ultra-violet (UV) and visible (VIS) channels since the sensitivity of nadir measurements decreases due to absorption of the gas near the surface and with decreasing wavelength. Firstly, to create a look-up table, synthetic radiances were calculated from the vector discrete ordinate radiative transfer (VLIDORT) model in the UV and VIS range using various parameters such as aerosol properties (e.g., aerosol optical depth, single scattering albedo, and aerosol loading height), geometry information (e.g., solar zenith angle, viewing zenith angle, and relative azimuth angle), NO2 vertical profile, and surface reflectance. Secondly, spectral fitting was performed at an interval of 1 nm from the center wavelength of 350 nm to 380 nm with a fitting window of about 30 nm to calculate the ratio of average NO2 SCDs in the VIS range to those in UV range. To validate the NO2 vertical profile retrieval algorithm, synthetic radiances were calculated based on NO2 vertical profiles with random values. NO2 vertical profiles are assumed to have exponential distribution and are generated with random NO2 upper limits with a range of 0 to 3 km, random total NO2 VCDs with a range of 1 to 5 × 1016 molecules cm-2, and a random relaxation parameter of exponential distribution with a range of 0.5 to 1.5. The results showed that the NO2 upper limit was 0.3 km or lower and the surface NO2 volume mixing ratio was estimated within 15% error. In addition, we also retrieved tropospheric NO2 vertical profiles using OMI LV1B radiance data.

End Text

How to cite: Hong, H., Park, J., and Lee, H.: Development of a novel method for Nitrogen Dioxide vertical profile retrieval , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13449, https://doi.org/10.5194/egusphere-egu2020-13449, 2020.

The lidar LIDAR system is widely used in atmospheric aerosol and boundary layer (BL) studies, and for the detection of cloud boundaries. However automatic and accurate identification of cloud top and bottom heights and BL height is not trivial, especially for low signal to noise ratio values, and for cloud layers below the top of BL, because of the disentanglement of cloud and aerosol contribution to LIDAR signal.

In this work, a signal threshold approach is presented, starting from the Range Corrected Signal (RCS) and using its spatial and temporal variations. The approach has been tested using one year of acquisitions of the elastic LIDAR hosted in the BAQUNIN (Boundary-layer Air QUality analysis using Network of INstruments) Supersite(https://www.baqunin.eu) with a spatial and temporal resolution of 7.5 m and 10 s, respectively.

A minimum threshold value T_c applied to the RCS values allows detecting the presence of a cloud layer. This approach could be applied to each type of acquired LIDAR elastic signal, but depends on the specific LIDAR channel characteristics, in particular the signal to noise ratio.

RCS values obtained for each acquired profile and altitude could be considered as a two-dimensional matrix M. As first step the elements M_ij>T_c of this matrix are labeled as possible cloud elements.

Subsequently, the algorithm excludes from the calculation the elements M_ij corresponding to spike values or affected by high noise considering the spatial and temporal variations of the RCS. A labeled element is confirmed to be a cloud element if the number of its labeled neighbors is above a selected percentage threshold T_perc. The grid of elements considered as neighbors can be defined according to spatial and temporal resolution of the LIDAR acquisition.

Finally, bottom and top of cloud layers are retrieved as the altitude of first and last labeled elements of each cloud layer and profile.

The accuracy of the results depends on the spatial and temporal resolution of the acquired signal, considering the BAQUNIN LIDAR characteristics the best accuracy is 15 m and 20 s.

The same approach could be used to distinguish aerosol from cloud layers, using a different threshold value for the aerosol.

This method was tested for different atmospheric conditions and results are discussed in this work.

How to cite: Iannarelli, A., Cacciani, M., Mevi, G., Casadio, S., and Di Bernardino, A.: An automatic algorithm for the detection and the characterization of cloud boundaries from BAQUNIN LIDAR signals, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21844, https://doi.org/10.5194/egusphere-egu2020-21844, 2020.

Measuring aerosol at high altitude sites is useful as it enables sampling of the free troposphere over long time frames. However, in order to draw conclusions from station measurement data, we need to determine which air mass sources are present at any given sampling time. This task is challenging at mountain sites, due to complex topography which in turn drives complex meteorology. Between December 2017 and May 2018, the Southern hemisphere high ALTitude Experiment on particle Nucleation And growth (SALTENA) campaign was conducted at Chacaltaya in Bolivia at 5240 m a.s.l. The data set obtained in this campaign contains records of nearly all relevant aerosol characteristics and aerosol precursors. To identify the source regions of the observed air masses we performed high resolution (down to 1 km) simulations with the Weather Research and Forecasting Model (WRF). The WRF model output is then used to as input to the Lagrangian particle dispersion model (FLEXPART). FLEXPART simulations are initialised every hour and 20 thousand particles are released per hour and track backwards in time for 96 hours. The FLEXPART footprint output is regridded onto a log-polar cylindrical grid where we perform a ‘K-means’ cluster analysis on the 3D cells defined by the grid. The cells are clustered based on the time series of their source receptor relationship (i.e. emission sensitivities), producing regions (clusters) resolved not only in the horizontal but also the vertical domain. Our results show that regions located close to the station (<100km) have a low but persistent influence with diurnal variations and close contact to the surface. Mid-range regions (100-800km) have the highest influence with a higher percentage of air masses from the free troposphere. Long-range regions (>800km) have a higher influence than the short-range regions but lower than the middle-range regions. Most of the air masses from these long-range regions come from the free troposphere. With this method we have successfully resolved the various air mass influences at the measurement site. The high meteorological resolution and the stochastic nature of FLEXPART are seminal for capturing the transport pathways.

How to cite: Aliaga, D., Sinclair, V., Qiaozhi, Z., Andrade, M., Mohr, C., and Krejci, R.: Source region cluster analysis in the high-altitude measuring site of Chacaltaya with WRF and FLEXPART, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18983, https://doi.org/10.5194/egusphere-egu2020-18983, 2020.

Open biomass burning (OBB) has large potential in triggering local and regional severe haze with elevated fine particulate matter (PM_2.5) concentrations and could thus deteriorate ambient air quality and threaten human health. Open crop straw burning (OCSB), as a critical part of OBB, emits abundant gaseous and particulate pollutants, especially in fields with intensive agriculture, such as central and eastern China (CEC).  However, uncertainties in current OCSB and other types of OBB emissions in chemical transport models (CTMs) lead to inaccuracies in evaluating their impacts on haze formations. Satellite retrievals provide an alternative that can be used to simultaneously quantify emissions of OCSB and other types of OBB, such as the Fire INventory from NCAR version 1.5 (FINNv1.5), which, nevertheless, generally underestimate their magnitudes due to unresolved small fires. In this study, we selected June in 2014 as our study period, which exhibited a complete evolution process of OBB (from June 1 to 19) over CEC. During this period, OBB was dominated by OCSB in terms of the number of fire hotspot and associated emissions, most of which were located at Henan and Anhui with intensive enhancements from June 5 to 14. OCSB generally exhibits spatiotemporal correlation with regional haze over the central part of CEC (Henan, Anhui, Hubei, and Hunan), while other types of OBB emissions had influences on Jiangxi, Zhejiang, and Fujian. Based on these analyses, we establish a constraining method that integrates ground-level PM_2.5 measurements with a state-of-art fully coupled regional meteorological and chemical transport model (the two-way coupled WRF-CMAQ) in order to derive optimal OBB emissions based on FINNv1.5. It is demonstrated that these emissions allow the model to reproduce meteorological and chemical fields over CEC during the study period, whereas the original FINNv1.5 underestimated OBB emissions by 2 ~ 7 times, depending on specific spatiotemporal scales. The results show that OBB had substantial impacts on surface PM_2.5 concentrations over CEC. Most of the OBB contributions were dominated by OCSB, especially in Henan, Anhui, Hubei, and Hunan, while other types of OBB emissions also exerted influence in Jiangxi, Zhejiang, and Fujian. With the concentration-weighted trajectory (CWT) method, potential OCSB sources leading to severe haze in Henan, Anhui, Hubei, and Hunan were pinpointed. The results show that the OCSB emissions in Henan and Anhui can cause haze not only locally but also regionally through regional transport. Combining with meteorological analyses, we can find that surface weather patterns played a cardinal role in reshaping spatial and temporal characteristics of PM_2.5 concentrations. Stationary high-pressure systems over CEC enhanced local PM_2.5 concentrations in Henan and Anhui. Then, with the evolution of meteorological patterns, Hubei and Hunan in the low-pressure system were impacted by areas enveloped in the high-pressure system. These results suggest that policymakers should strictly undertake interprovincial joint enforcement actions to prohibit irregular OBB, especially OCSB over CEC. Constrained OBB emissions can, to a large extent, supplement estimations derived from satellite retrievals as well as reduce overestimates of bottom-up methods.

How to cite: Li, P., Yu, S., Wu, Y., Mehmood, K., Wang, L., Chen, X., Li, Z., Zhang, Y., Li, M., Liu, W., Zhu, Y., Rosenfeld, D., and Seinfeld, J. H.: Relative effects of open biomass and crop straw burning on haze formation over central and eastern China: modelling study driven by constrained emissions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12507, https://doi.org/10.5194/egusphere-egu2020-12507, 2020.

How to cite: Craine, N.: Unmanned Stratospheric Glider for Satellite Calibration, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9447, https://doi.org/10.5194/egusphere-egu2020-9447, 2020.

Southeast Asia has a far-reaching influence on the atmospheric distribution of aerosols and co-emitted trace gasses due to the high amount of emissions, the large contribution from co-emitted heat (i.e. biomass burning and urbanization), the highly variable topography, and intense and variable meteorology. We aim to quantify the pathways and constrain the impact of long-range transport on the measured increase in aerosol loading and variability. When the dry season comes in January through April, a large number of aerosols are discharged into the atmosphere from Myanmar, Thailand, Cambodia and Vietnam, which in theory, should transport them to the East under the influence of the Indian monsoon. What we observe is that first, this eastward transport is much larger in area than expected, with measurements clearly showing aerosols and long-lived trace gasses passing Taiwan and winding up in the Central Pacific, or passing around Taiwan and winding up in Northeastern China, Korea, and Japan. Secondly, we observe a significant although smaller transport of aerosols far to the south, breaching the equator, even though the climatology at this time of year indicates a Monsoon belt from 7^oN southward.

We first employ a new emissions spatial-temporal distribution, forced by remotely sensed measurements of trace gasses, and second we consider meteorology associated with both fire plumes and mountain slopes. The combination of these forcings we argue is essential to reconstruct the observations. We second use observations from dozens of AERONET sites located in Southeast Asia from 2010 to 2018, to obtain the distribution of extreme events of AOD and AAOD. In addition, we combine precipitation from TRMM. These are used in tandem to establish the structural observational relationship between emissions, rainfall, transport, and diffusion.

We run these new emissions in the WRF-CHEM framework and observe a strong improvement in comparison with the measured means and variability of aerosols from MODIS and MISR, gasses from MOPITT. Furthermore, we observe a change in the vertical distribution and location of the large-scale meteorology itself, indicating that there is a possible important two-way feedback at work. We specifically note that there are significant changes induced in the high rainfall days, and in the loadings of aerosols and wind in the region from 800 to 950 hPa, with different sized particles segregated into different height levels.

How to cite: Wang, S. and Cohen, J. B.: A New Approach to Quantify the Transport of Extreme Aerosol Events in Southeast Asia by Combining WRF-CHEM with Various Models and Remotely Sensed Measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9465, https://doi.org/10.5194/egusphere-egu2020-9465, 2020.

Formaldehyde is a key intermediate in photochemical oxidation of volatile organic compounds in the troposphere and is also directly emitted by a range of sources, including biomass burning and fuel combustion. Airborne measurements of formaldehyde have therefore been used to investigate oxidation in biomass burning (BB) plumes intercepted during the Methane Observations and Yearly Assessments (MOYA) campaign. The MOYA campaign took place January/February 2019 in Uganda and Zambia and mixing ratios of formaldehyde were obtained using the University of Leeds formaldehyde Laser Induced Fluorescence (LIF) instrument. A range of air masses were intercepted including multiple near-field biomass burning (BB) plumes, with up to 140 ppb of formaldehyde observed, and urban emission plumes from the capital city of Kampala in Uganda, where up to 7 ppb of formaldehyde was measured. Formaldehyde emission factors have been calculated for Ugandan BB (1.20 ± 0.23 g kg^-1) which agree well with literature (1.23 ± 0.65 g kg^-1) for Savannah combustion. Production of formaldehyde as a function of plume age has also been investigated in order to discriminate direct emission from photochemical formation in BB plumes. BB plumes were also intercepted during other aircraft campaigns several days downwind of emission such as a plume transported from Canadian wildfires observed in the North Atlantic during ACSIS-5/ARNA-1 where levels of up to 18.30 ppb were detected, indicative of sustained photochemical oxidation within the plume. Comparison of urban, near-field BB and far-field BB plumes provides a variety of environments and photochemical ages to test our understanding of combustion oxidation processes.

How to cite: Ronnie, G., Whalley, L., Heard, D., Ingham, T., Lee, J., Pasternak, D., Bauguitte, S., Carling, R., Bannan, T., Wu, H., and Archibald, A.: Airborne Measurements of Formaldehyde In Biomass Burning and Urban Plumes In Central Africa Using Laser Induced Fluorescence , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2998, https://doi.org/10.5194/egusphere-egu2020-2998, 2020.

Marine ecosystems are an important component of the climate feedback system. One of the main pathways for ocean-climate interaction is through the oxidation of DMS (dimethyl sulphide), a gas released from phytoplankton in the sea surface. DMS derived products are known to be important in marine cloud formation and the Earth’s radiation budget. Aerosol-Cloud interactions currently represent the largest uncertainty in climate modelling (Boucher et al., 2013). Our research focuses on airborne measurements using real-time high resolution instruments to identify and quantify trace oceanic biogenic gases on board the FAAM research aircraft. Here we present aircraft measurements made over the North Atlantic ocean using a HR-ToF-CIMS, across three seasons during the most recent ACSIS/ARNA campaigns. Here we report some of the first observations of an alternative DMS oxidation product, hydperoxymethyl thioformate (HPMFT) using chemical ionisation mass spectrometry with iodide reagent ion. Observations of this novel species have never been reported in the atmosphere but laboratory studies suggest that the main oxidation route of DMS occurs through this species, in certain environments (Berndt et al., 2019). This has potentially significant climate implications, none of which are currently represented in global climate models. The fate of this newly measured species once in the atmosphere is uncertain but is likely to alter our understanding of the marine sulphur cycle. These observations along with laboratory and modelling studies will aid in being able to understand the role of HPMFT in the ocean-climate feedback system.

References

T. Berndt, W. Scholz, B. Mentler, L. Fischer, E. H. Hoffmann, A. Tilgner, N. Hyttinen, N. L. Prisle, A. Hansel, and H. Herrmann, The Journal of Physical Chemistry Letters 2019 10 (21), 6478-6483,DOI: 10.1021/acs.jpclett.9b02567

Boucher O, Randall D, Artaxo P, Bretherton C, Feingold G, Forster P, Kerminen VM, Kondo Y, Liao H, Lohmann U, Rasch P, Satheesh S, Sherwood S, Stevens B, Zhang X. In: Clouds and aerosols. Cambridge: Cambridge University Press; 2013. United Kingdom and new york, NY, USA, book section Chapter 7, pp 571–658. https://doi.org/10.1017/CBO9781107415324.016.

How to cite: Matthews, E., Bannan, T., Mehra, A., Archibald, A., Wu, H., Williams, P., Lee, J., Veres, P., Percival, C., Coe, H., and Gallagher, M.: Aircraft observations of a new DMS oxidation product over the North Atlantic using a HR-ToF-CIMS, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18077, https://doi.org/10.5194/egusphere-egu2020-18077, 2020.

Organic aerosol (OA) is one of the major contributors to the PM2.5 burden both in the continental Northern Hemisphere and globally. Understanding its sources and aging is central to current air quality control strategies. For the remote troposphere, sparse in-situ data to date results in highly under constrained OA prediction models, with model diversity of up to three orders of magnitude in the recent AEROCOM-II comparison.  

In the course of the recent NASA Atmospheric Tomography (ATom) set of aircraft missions, we have acquired four unique global datasets of submicron aerosol concentration and composition over the remote Atlantic and Pacific Oceans. In the remote FT OA and sulfate are the main components (about 0.3 µg sm-3 in total, fairly constant outside of continental outflow. However, OA in the remote FT exhibits a much higher average carbon oxidation state than in continental airmasses (OSc up to +1 compared to -1 over the continents), much higher than assumed in most models. This also suggests a fairly hygroscopic OA. Nevertheless, in the cleanest/most remote parts of the global free troposphere (FT), sulfate predominates. This is not captured by current global models and suggests an additional chemical removal of OA (and possibly continuing formation of sulfate).

Using several different hydrocarbon-ratio based photochemical clocks in combination with back trajectories to infer the age of the airmasses sampled during ATom, we estimate that the lifetime of OA in the remote UT (after most of the convective removal has happened) is of the order of 4 days. In contrast, for chemically inert black carbon, the estimated removal timescale using the same method is significantly longer (about a week), in general agreement with previous estimates of physical removal that are used in models. The significantly shorter OA lifetime suggests an additional, chemical removal mechanism. This provides a key constraint for modeling of OA in the FT, based solely on measurements.  Both heterogeneous oxidation by OH and aerosol photolysis are possible pathways for OA removal that have been suggested previously. Sensitivity studies in CESM2 AND GEOS-Chem with updated chemistry and aerosol sources are used to constrain the relative importance of each pathway for OA removal during ATom.

How to cite: Campuzano-Jost, P., Nault, B., Schroder, J., Jo, D., Day, D., Hodzic, A., Tilmes, S., Emmons, L., Ray, E., Yu, P., Bian, H., Chin, M., Colarco, P., Newman, P., Kodros, J., Pierce, J., Schacht, J., Heinold, B., Tegen, I., and Jimenez, J. L. and the ATom Science Team: Quantifying organic aerosol removal in the remote troposphere: Constraints on physical and chemical removal of OA provided by the ATom mission, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6155, https://doi.org/10.5194/egusphere-egu2020-6155, 2020.

Interactions of meteorology with wildfires in British Columbia, Canada during August 2017 led to several extreme pyrocumulonimbus (PyroCb) events that resulted in the injection of smoke aerosols and other combustion products into the lower stratosphere. These plumes of stratospheric smoke were observed by many satellite instruments to have elevated values of aerosol extinction and backscatter compared to the background state and were readily tracked as they spread across the Northern Hemisphere and resided in the lower stratosphere for about ten months following the fires. To investigate the radiative impacts of these events on the Earth system, we performed a number of simulations with the Goddard Earth Observing System (GEOS) global Earth system model, which includes detailed aerosol and chemistry packages coupled to the underlying model physical and dynamical cores. Retrievals of smoke aerosol properties from space-based OMPS/NPP, SAGE-III/ISS, and CALIOP/CALIPSO instruments were used to calibrate the injection location, timing, amount, and optical properties of the smoke aerosols. The resulting simulations of three-dimensional smoke transport were evaluated over a year following the injections using observations from OMPS-Limb Profiler (LP), which provides aerosol retrievals at a high temporal and vertical resolution for altitudes greater than 10 km. We found that diabatic heating due to aerosol absorption, combined with the large-scale atmospheric motions, play important roles in lifting the smoke plumes from near the tropopause altitudes to about 22 km into the atmosphere. The model was able to simulate the rate of plume ascent from lower to the middle stratosphere, hemispherical spread and residence time of the smoke aerosols in the stratosphere in close agreement with OMPS-LP. Finally, we also investigated the impact of these PyroCb emitted smoke aerosols on the stratospheric radiative forcing and the subsequent impact on temperature tendencies.

How to cite: Das, S., Colarco, P., Oman, L., Taha, G., and Torres, O.: Pyrocumulonimbus Events over British Columbia, 2017: The Long-term Transport and Radiative Impacts of Smoke Aerosols in the Stratosphere , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11119, https://doi.org/10.5194/egusphere-egu2020-11119, 2020.