Fine-particle pollution associated with haze threatens the health of more than 1 billion people in China. Extremely high PM2.5 concentrations are frequently observed especially during the winter haze event in northern China. Even after accounting for aerosol-radiation-meteorology feedback and improving the emission inventory, state-of-the-art models still fail to capture the observed high PM2.5 concentrations, suggesting the missing of key chemistry for the secondary aerosol formation. To improve the prediction and control strategy of PM2.5, we are in urgent need of a better understanding of the chemistry of secondary aerosol formation. Thus we propose the session "Multiphase chemistry of secondary aerosol formation under severe haze" to promote the research and discussion on this topic which is highly relevant for both atmospheric chemists and the public.
The session is open for all submissions which addresses, but is not limited to, the following questions concerning secondary aerosol formation: What are the key oxidation pathways leading to aerosol formation under clean and polluted conditions? What is the role of multiphase chemistry versus gas phase chemistry? Are laboratory determined kinetic data of multiphase chemistry directly applicable for ambient conditions and if not, how to derive and determine the reaction kinetics relevant for ambient conditions? What is the aerosol particles’ and droplets’ pH and how does it influence the multiphase chemistry? What is the role of the RH, temperature, mixing state and aerosol phase state in multiphase chemistry and how does aerosol mixing state play a role? What's the contribution of aqueous secondary organic aerosol (SOA) formation under highly polluted conditions?
A special issue of the same topic has already been approved and launched in the EGU journal "Atmospheric Chemistry and Physics".
vPICO presentations: Tue, 27 Apr
The pandemic of SARS-CoV-2 has led to a substantial reduction in anthropogenic activities globally. This is particularly true for traffic, which was reduced by 40-80 % in Eastern and Northern China. The imposed lockdown provides a unique opportunity to investigate the direct and indirect effects of anthropogenic activities (particularly traffic) on atmospheric new particle formation, atmospheric chemical cocktail and haze formation in polluted urban environments in the case when the emissions were substantially lower. Here, we utilize comprehensive, long term ground-based and satellite observations to investigate changes in the atmospheric composition and connect them with a continental scale gas-to-particle conversion producing both fresh particles and new aerosol mass. We show that despite the reductions in emissions, both new particle formation (NPF) and haze events still occur. The observational evidence confirms that the main NPF mechanism remains similar because of non-linear response of NPF and growth to local and regional vehicle emission reductions. Furthermore we are able follow the growth from NPF to haze and show, in the case study, that regional NPF makes a dominating contribution to the haze.
How to cite: Kulmala, M., Yan, C., Dada, L., Bianchi, F., Kokkonen, T., and Jiang, J. and the Aerosol and Haze Laboratory Team: The effect of COVID-19 restrictions of human activities on atmospheric chemical cocktail, new particle formation and air quality in in Eastern and Northern China, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12589, https://doi.org/10.5194/egusphere-egu21-12589, 2021.
In the recent decade, frequently occurring severe haze events in the North China Plain (NCP) have triggered numerous studies on the underlying formation mechanisms, and the contribution of multiphase chemistry on haze formation becomes one of the focal points. The Multiphase chemistry experiment in Fogs and Aerosols in the North China Plain (McFAN) investigated the physicochemical mechanisms leading to haze formation with a focus on the contributions of multiphase processes in aerosols and fogs. We integrated observations on multiple platforms with regional and box model simulations to identify and characterize the key oxidation processes producing sulfate, nitrate and secondary organic aerosols. An outdoor twin-chamber system was deployed to conduct kinetic experiments under real atmospheric conditions in comparison to literature kinetic data from laboratory studies. The experiments were spanning multiple years since 2017 and an intensive field campaign was performed in the winter of 2018. The location of the site minimizes fast transition between clean and polluted air masses, and regimes representative for the North China Plain were observed at the measurement location in Gucheng near Beijing. The consecutive multi-year experiments document recent trends of PM2.5 pollution and corresponding changes of aerosol physical and chemical properties, enabling in-depth investigations of established and newly proposed chemical mechanisms of haze formation. This study is mainly focusing on the data obtained from the winter campaign 2018. To investigate multiphase chemistry, the results are presented and discussed by means of three characteristic cases: low humidity, high humidity and fog. We find a strong relative humidity dependence of aerosol chemical compositions, suggesting an important role of multiphase chemistry. Compared with the low humidity period, both PM1 and PM2.5 show higher mass fraction of secondary inorganic aerosols (SIA, mainly as nitrate, sulfate and ammonium) and secondary organic aerosols (SOA) during high humidity and fog episodes. The changes in aerosol composition further influence aerosol physical properties, e.g., with higher aerosol hygroscopicity parameter k and single scattering albedo SSA under high humidity and fog cases. The campaign-averaged aerosol pH is 5.1 ± 0.9, of which the variation is mainly driven by the aerosol water content (AWC) concentrations. Overall, the McFAN experiment provides new evidence of the key role of multiphase reactions in regulating aerosol chemical composition and physical properties in polluted regions.
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How to cite: Li, G., Su, H., Kuhn, U., Zheng, G., Pöschl, U., and Cheng, Y. and the McFAN team: Multiphase chemistry experiment in Fogs and Aerosols in the North China Plain (McFAN): integrated analysis and intensive winter campaign 2018, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8388, https://doi.org/10.5194/egusphere-egu21-8388, 2021.
Aerosol acidity is a key parameter in atmospheric aqueous chemistry and strongly influence the interactions of air pollutants and ecosystem. The recently proposed multiphase buffer theory provides a framework to reconstruct long-term trends and spatial variations of aerosol pH based on the effective acid dissociation constant of ammonia (Ka,NH3*). However, non-ideality in aerosol droplets is a major challenge limiting its broad applications. Here, we introduced a non-ideality correction factor (cni) and investigated its governing factors. We found that besides relative humidity (RH) and temperature, cni is mainly determined by the molar fraction of NO3- in aqueous-phase anions, due to different NH4+ activity coefficients between (NH4)2SO4- and NH4NO3-dominated aerosols. A parameterization method is thus proposed to estimate cni at given RH, temperature and NO3- fraction, and is validated against long-term observations and global simulations. In the ammonia-buffered regime, with cni correction the buffer theory can well reproduce the Ka,NH3* predicted by comprehensive thermodynamic models, with root-mean-square deviation ~0.1 and correlation coefficient ~1. Note that, while cni is needed to predict Ka,NH3* levels, it is usually not the dominant contributor to its variations, as ~90% of the temporal or spatial variations in Ka,NH3* is due to variations in aerosol water and temperature.
How to cite: Cheng, Y., Zheng, G., Su, H., Wang, S., and Pozzer, A.: The impact of non-ideality on reconstructing spatial and temporal variations of aerosol acidity with multiphase buffer theory, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9292, https://doi.org/10.5194/egusphere-egu21-9292, 2021.
Understanding the mechanism of haze formation is crucial for the development of deliberate pollution control strategies. Multiphase chemical reactions in aerosol water have been suggested as an important source of particulate sulfate during severe haze (Cheng et al., 2016;Wang et al., 2016). While the key role of aerosol water has been commonly accepted, the relative importance of different oxidation pathways in the aqueous phase is still under debate, mainly due to questions about aerosol pH. To investigate the spatio-temporal variability of aerosol pH and sulfate formation during winter in the North China Plain (NCP), we have developed a new aerosol water chemistry module (AWAC) for the WRF-Chem model (Weather Research and Forecasting model coupled with Chemistry). Using the WRF-Chem-AWAC model, we performed a comprehensive survey of the atmospheric conditions characteristic for wintertime in the NCP, focusing on January 2013. We find that aerosol pH exhibited a strong vertical gradient and distinct diurnal cycle, which was closely associated with the spatio-temporal variation in the relative abundance of acidic and alkaline fine particle components and their gaseous counterparts. Over Beijing, the average aerosol pH at the surface layer was ~5.4 and remained nearly constant around ~5 up to ~2 km above ground level; further aloft, the acidity rapidly increased to pH ~0 at ~3 km. The pattern of aerosol acidity increase with altitude persisted over the NCP, while the specific levels and gradients of pH varied between different regions. In the region north of ~41°N, the mean pH values at surface level were typically >6 and the main pathway of sulfate formation in aerosol water was S(IV) oxidation by ozone. South of ~41°N, the mean pH values at surface level were typically in the range of 4.4 to 5.7, and different chemical regimes and reaction pathways of sulfate formation prevailed in four different regions, depending on reactant concentrations and atmospheric conditions. The NO2 reaction pathway prevailed in the megacity region of Beijing and the large area of Hebei Province to the south and west of Beijing, as well as part of Shandong Province. The transition metal ion (TMI) pathway dominated in the inland region to the west and the coastal regions to the east of Beijing, and the H2O2 pathway dominated in the region extending further south (Shandong and Henan Provinces). In all of these regions, the O3 and TMI pathways in aerosol water as well as the gas-particle partitioning of H2SO4 vapor became more important with increasing altitude. Although pH is sensitive to the abundance of NH3 and crustal particles, we show that the rapid production of sulfate in the NCP can be maintained over a wide range of aerosol acidity (e.g., pH = 4.2-5.7) with transitions from TMI pathway dominated to NO2/O3 pathway dominated regimes.
How to cite: Tao, W., Su, H., Zheng, G., Wang, J., Wei, C., Liu, L., Ma, N., Li, M., Zhang, Q., Pöschl, U., and Cheng, Y.: Aerosol pH and chemical regimes of sulfate formation in aerosol water during winter haze in the North China Plain, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7189, https://doi.org/10.5194/egusphere-egu21-7189, 2021.
Reactive oxygen species (ROS), such as hydroxyl radical (OH•), hydroperoxy radicals (HO2•/O2-), and hydrogen peroxide (H2O2), are produced in cloud droplets and aqueous aerosol. Multiphase model studies suggest that the Fenton reaction, i.e. the oxidation of Fe(II) by H2O2 represents one of the main sources of the OH radical in the aqueous phase.
Current cloud and aerosol multiphase chemistry models are usually initialized with equal iron concentrations in all droplets or particles as derived from bulk samples of cloud water or aerosol composition. However, analysis of single aerosol particles has revealed that only a small number fraction of particles and, thus, of cloud droplets contain iron.
The aim of our study is to identify the impacts of the iron distribution in cloud droplets or aqueous aerosol particles on the total (gas + aqueous) budgets of OH, HO2, H2O2 and O3 in the multiphase system.
By means of model studies, we compare predicted oxidant budgets based on the assumptions of iron distributed among all droplets or particles versus the same iron mass concentrated in a few droplets (or particles) in the total population only. Our results suggest that the traditional approach based on bulk iron concentrations may significantly underestimate total OH budgets, whereas the predicted levels of H2O2, HO2/O2- and ozone are less affected. The reasons for the different findings between (i) the various oxidants and (ii) cloud droplets vs aerosol particles will be discussed. In summary, our model studies suggest that oxidant levels and oxidation potentials of particulate matter in the atmosphere can only be accurately assessed if particle- and size-resolved aerosol composition is accounted for.
How to cite: Khaled, A., Zhang, M., and Ervens, B.: The impact of iron distribution among cloud droplets or aqueous aerosol particles on multiphase oxidant levels, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2102, https://doi.org/10.5194/egusphere-egu21-2102, 2021.
Hydrolysis of nitrogen dioxide (NO2) has long been recognized as a major formation path of atmospheric nitrous acid (HONO), which is regarded as a dominant hydroxyl radical (OH) source, particularly in a polluted environment. Since HONO is moderately water soluble and its solubility can be highly dependent on the acidity of the water solution, the HONO formation rate and its ensuring fate may also be affected by the acidity of the water surfaces. In this work, we investigated the hydrolysis of NO2 on dilute sulfuric acid water solutions with a pH value ranging from ~3 to ~6. Both the gaseous HONO and dissolved nitrous acid solution were quantified by a wet-chemistry based HONO analyzer and ion chromatography analyses, respectively. The results showed that significant amount of HONO can participate into the aqueous phase at low acidity and as the acidity increased gas-phase HONO also increased. These results indicated that liquid water on various surfaces may both provide a reaction site for HONO formation and serve as a reservoir of HONO that can be released when the liquid water was evaporated.
How to cite: Zheng, J. and Ma, Y.: Heterogeneous formation and partitioning of nitrous acid on water surfaces: dependency on the acidity, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2114, https://doi.org/10.5194/egusphere-egu21-2114, 2021.
The rapid formation of sulphate is the main driving force behind the explosive growth of PM2.5 in China. Our comprehensive study, combined with field observations, laboratory simulations and modelling, indicated that high concentration of hydroperoxide (H2O2) from heterogeneous reactions significantly promoted sulphate formation in winter north China. Unexpectedly, during the same campaign, a high proportion of sulphate has been observed in the frost. The chemical composition of the frost appeared to be independent of that of PM2.5. These findings can be important for the removal rate of SO2 in the atmosphere and for the occult deposition of sulphate.
Also, we have investigated the contribution of oxidation channels to sulphate formation in the cloud at the summit of Mt. Tai (1545 m) in summer. Our results suggested that dissolved ozone is the dominant oxidant for the oxidation of S(IV), especially when the pH of the cloud water is less acidic (> 5.5). In recent years, with the increase of ozone concentration in China, the sulphate formation by ozone in the cloud will continue to be pronounced.
Zhu, C., Li, J.R., Chen, H., Cheng, T.T., Wen, L., Herrmann, H., Xiao, H., Chen, J.M., 2020. Inorganic composition and occult deposition of frost collected under severe polluted area in winter in the North China Plain. Science of the Total Environment 722.
Li, J.R., Zhu, C., Chen, H., Zhao, D.F., Xue, L.K., Wang, X.F., Li, H.Y., Liu, P.F., Liu, J.F., Zhang, C.L., Mu, Y.J., Zhang, W.J., Zhang, L.M., Herrmann, H., Li, K., Liu, M., Chen, J.M., 2020. The evolution of cloud and aerosol microphysics at the summit of Mt. Tai, China. Atmospheric Chemistry and Physics 20, 13735-13751.
How to cite: Chen, H., Li, J., Zhu, C., Herrmann, H., and Chen, J.: Heterogeneous sulphate formation in the aerosol, the cloud and the frost, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4039, https://doi.org/10.5194/egusphere-egu21-4039, 2021.
Nitrous acid (HONO) is an important component of the nitrogen cycle. HONO can also be rapidly photolyzed by actinic radiation to form hydroxyl radicals (OH) and exerts a primary influence on the oxidative capacity of the atmosphere. The sources and sinks of HONO, however, are not fully understood. Soil nitrite, produced via nitrification or denitrification, is an important source for the atmospheric HONO production. [HONO]*, the equilibrium gas phase HONO concentration over the soil, has been suggested as key to understanding the environmental effects of soil fluxes of HONO (Su et al., 2011). But if and how [HONO]* may exist and vary remains an open question. In this project, a measurement method using a dynamic chamber has been developed to derive [HONO]* and the atmospheric soil fluxes of HONO can accordingly be quantified. We demonstrate the existence of [HONO]* and determine its variation in the course of soil drying processes. We show that when [HONO]* is higher than the atmospheric HONO concentration, HONO will be released from soil; otherwise, HONO will be deposited on soil. This work advances the understanding of soil HONO emissions, and the evaluation of its impact on the atmospheric oxidizing capacity and the nitrogen cycling.
How to cite: Bao, F., Su, H., Kuhn, U., and Cheng, Y.: Key Role of Equilibrium HONO Concentration over the Soil , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4166, https://doi.org/10.5194/egusphere-egu21-4166, 2021.
Interactions between water and nanoparticles are of great significance for atmospheric multiphase processes, physical chemistry, and materials science. Current knowledge of the hygroscopic and related physicochemical properties of nanoparticles, however, is insufficient due to limitations of the available measurement techniques. Here, we present the design and performance of a nano-hygroscopicity tandem differential mobility analyzer (nano-HTDMA) apparatus. To enable high accuracy and precision in hygroscopicity measurements of sub-10 nm aerosol nanoparticles, systematic and comprehensive calibration criteria of nano-HTDMA have been developed and applied, including sheath/aerosol flow rates, DMA voltage, relative humidity (RH) sensor, temperature sensor, and particle sizing. After calibration, the nano-HTDMA system has been shown to have an accurate sizing and a small sizing offsets between the two DMAs (<1.4%) for aerosol nanoparticles with diameters down to 6 nm. Moreover, to maintain the RH-uniformities that prevent the pre-deliquescence and non-prompt phase transition of nanoparticles within DMA2, the RH of sheath flow is kept as same as that of aerosol flow at inlet of DMA2, and the humidification system and the DMA2 system are placed in a well-insulated and air conditioner housing (±0.1K). Using nano-HTDMA system. We investigate the hygroscopic behavior of aerosol nanoparticles of two inorganic substances (e.g., ammonium sulfate and sodium sulfate). A strong size dependence of the hygroscopic growth factor is observed for ammonium sulfate and sodium sulfate nanoparticles with diameters down to 6 nm, respectively. For size dependence of phase transition, we find a weak size dependence of DRH and ERH of ammonium sulfate nanoparticles with diameters from 6 to 100 nm but a pronounced size dependence of DRH and ERH between 20 and 6 nm for sodium sulfate nanoparticles.
How to cite: Lei, T., Ma, N., Hong, J., Tuch, T., Wang, X., Wang, Z., Pöhlker, M., Ge, M., Wang, W., Mikhailov, E., Hoffmann, T., Pöschl, U., Su, H., Wiedensohler, A., and Cheng, Y.: Nano-HTDMA for investigating hygroscopic properties of sub-10 nm aerosol nanoparticles, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6310, https://doi.org/10.5194/egusphere-egu21-6310, 2021.
Measuring pH in individual aerosol droplet is essential for understanding and estimating physicochemical processes within aerosol microenvironments. Recently, aerosol optical tweezers coupling with Raman spectroscopy have been applied to measure the pH of single trapped microdroplets by utilizing conjugate acid-base equilibrium to infer pH shifts. However, such measurements are easily affected by many factors such as variations in detecting volumes and laser intensities, making it hard to directly determine these acid and base concentrations through their respective peak areas. To overcome these problems and accurately measure the concentrations of SO42- and HSO4− within individual NaHSO4 microdroplets, in this study a ratio-metric spectroscopic method is developed based on the peak area ratio of ν(SO42−)/ν(OH) and ν(HSO4−)/ν(OH). Combined with the ion balance and ion activity coefficients, droplet pH is determined unambiguously. These experiment results were further used to evaluate the performance of activity models and thermodynamic models associated with aerosol pH, ion concentration and activity coefficient predictions. Pitzer, Simonson, and Clegg (PSC) model provides the best predictions of ion activity coefficients Extended Aerosol Inorganics Model vision IV (E-AIM IV) works well over a wide NaHSO4 concentration range (0.4-8.8 mol/kg), while ACCENT Pitzer model predictions have extremely good agreement with the experiment results in low NaHSO4 concentration condition (≤2.0 mol/kg). By contrast, ISORROPIA II shows relatively poor performance as compared with E-AIM IV.
How to cite: Li, M., Su, H., Zheng, G., Kuhn, U., Li, G., Ma, N., Pöschl, U., and Cheng, Y.: Individual Aerosol Droplet pH Measurement via a Ratio-metric Raman Method Using Aerosol Optical Tweezers: Evaluation of Thermodynamic and Activity Models, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8057, https://doi.org/10.5194/egusphere-egu21-8057, 2021.
For understanding and assessing aerosol-cloud interactions and their impact on climate, reliable measurement data of aerosol particle hygroscopicity and cloud condensation nuclei (CCN) activity are required. Furthermore, aerosol liquid water, mainly controlled by hygroscopicity, affects heterogeneous and multiphase reactions of aerosol particles. The CCN activity of aerosol particles can be determined by scanning particle size and supersaturation (S) in the CCN measurement. Compared to the existing CCN activity measurement, a broad supersaturation scanning CCN (BS2-CCN) system, in which particles are exposed to a range of S simultaneously, can measure particle hygroscopicity and CCN activity with a high-time resolution. Based on a monotonic relation between the activation supersaturation of aerosol particles (Saerosol) and the activation fraction (Fact) of the BS2-CCN measurement, we can derive κ, a single hygroscopicity parameter, directly.
Here, we describe how the BS2-CCN system can be effectively calibrated and which factors can affect the calibration curve (Fact - Saerosol). For calibration, size-resolved CCN measurements with ammonium sulfate (AS) and sodium chloride particles are performed under the three different thermal gradient (dT) conditions (dT=6, 8, and 10). First, the shape of the calibration curve is primarily influenced by Smax, maximum S in the activation tube. We need to determine appropriate Smax depending on particle size and κ to be investigated. To minimize the effect of double/multiple charged particles, small Dg and σg in number size distribution are recommended when generating the calibration aerosols. Sheath-to-aerosol-flow ratio (SAR) is the third factor to be considered. BS2-CCNC system uses a low SAR with a wider inlet compared to the typical CCN measurement, which can make a monotonic relation between Fact and Saerosol. Lastly, Fact is affected by particle number concentration and has a decreasing rate of 0.02/100 cm-3 (within NCN ~ 300 cm-3 for AS) due to the water consumption in the chamber. For evaluating the BS2-CCN system, inter-comparison experiments between typical DMA-CCN and BS2-CCN measurement were performed with the laboratory-generated aerosol mixture and ambient aerosols. Statistically good agreements of κ values between DMA-CCN and BS2-CCN measurements for both inter-comparison experiments imply that the BS2-CCN system can measure particle hygroscopicity and CCN activity well compared to the existing measurement. We expect that this new system can be applied to aircraft and ship measurements that require a high-time resolution as well as ground measurement for a broad range of hygroscopicity distribution. Because hygroscopicity is closely related to the fraction of organics/inorganics in aerosol particles, our method can also serve as a complementary approach for fast detection/estimation of aerosol chemical compositions.
How to cite: Kim, N., Cheng, Y., Ma, N., Pöhlker, M., Klimach, T., Mentel, T., Pöschl, U., and Su, H.: Rapid measurement of particle hygroscopicity and CCN activity using broad scanning supersaturation (BS2)-CCNC: calibration and intercomparison, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8067, https://doi.org/10.5194/egusphere-egu21-8067, 2021.
Effective density is one of the most important physical properties of atmospheric aerosol particles, and is linked to particle formation and aging process. Combined characterization of aerosol density, chemical composition, emission and aging processes may provide crucial information for better understanding their interactions and effects on environment and climate. In autumn of 2019, the effective density of sub-micrometer aerosol particles was measured in-situ at a heavily polluted rural site in the North China Plain (NCP). A tandem technique coupling a Centrifugal Particle Mass Analyzer (CPMA) with a differential mobility analyzer (DMA) and a Condensation Particle Counter (CPC) were used to determine the effective density of ambient aerosol particles with diameters of 50, 100, 150, 220 and 300 nm. The probability distribution of effective density exhibits double peak modes in majority cases, with a higher density mode (main-density) and a lower density mode (sub-density). The existence of sub-density particles normally ascribed to freshly emitted or partial aged black carbon (BC) with non-spherical morphology. The number fraction of sub-density mode varies from 4% to 67%, with mean of 22-27% at five particle sizes. Due to the higher aging degree of larger particles, the main-density exhibits an evident ascending trend with particle size. However, the sub-density decreases as mobility size increases, from 0.89 g/cm3 at 50 nm to 0.62 g/cm3 at 300 nm, since larger fresh soot particles usually present a more agglomerated morphology than small particles. A comparison was carried out between the mean effective density at 300 nm and ACSM-derived density using different approximations of BC density. The best agreement is achieved when assuming a BC density of 0.6 g/cm3, indicating that BC typically exists as non-spherical particles with fractal-like or porous morphology in the NCP in cold season.
How to cite: Zhou, Y., Ma, N., Wang, Z., Tao, J., Hong, J., Peng, L., Xie, L., Zhu, S., Chen, C., Zhang, Q., Su, H., and Cheng, Y.: Size-resolved effective density of submicron aerosol particles in the North China Plain, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16424, https://doi.org/10.5194/egusphere-egu21-16424, 2021.
Simultaneous measurements of aerosol hygroscopicity and chemical composition were performed at a suburban site in the North China Plain in winter 2018 using a self-assembled hygroscopic tandem differential mobility analyzer (H-TDMA) and a capture-vaporizer time-of-flight aerosol chemical speciation monitor (CV-ToF-ACSM), respectively. During the experimental period, aerosol particles usually show an external mixture in terms of hygroscopicity, with a less hygroscopic particles mode (LH) and a more hygroscopic mode (MH). The average ensemble mean hygroscopicity parameter (κmean) are 0.16, 0.18, 0.16, and 0.15 for 60, 100, 150, and 200 nm particles, respectively. Two episodes with different RH/T conditions and secondary aerosol formations are distinguished. Higher aerosol hygroscopicity is observed for all measured sizes in the high RH episode (HRH) than in the low RH episode (LRH). In LRH, κ decreases as the particle size increases, which may be explained by the large contribution of non- or less-hygroscopic primary compounds in large particles due to the enhanced domestic heating emissions at low temperature. The number fraction of LH mode at 200 nm even exceeds 50%. Closure analysis is carried out between the HTDMA-measured κ and the ACSM-derived hygroscopicity using different approximations for the hygroscopic parameters of organic compounds (κorg). The results indicate that κorg is less sensitive towards the variation of its oxidation level under HRH conditions but has a stronger O: C-dependency under LRH conditions. The difference in the chemical composition and their corresponding physical properties under different RH/T conditions reflects potentially different formation mechanisms of secondary organic aerosols at those two distinct episodes.
How to cite: Shi, J., Hong, J., Ma, N., Luo, Q., Xu, H., Tan, H., He, Y., wang, Q., Tao, J., Zhou, Y., Peng, L., Cheng, Y., Su, H., and Sun, Y.: On the difference of aerosol hygroscopicity between high and low RH environment in the North China Plain, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13951, https://doi.org/10.5194/egusphere-egu21-13951, 2021.
Primary organic aerosol (POA) is a major component of PM2.5 in winter polluted air in the North China Plain (NCP), but our understanding on the atmospheric aging process of POA particles and the resulting influences on their optical properties is limited. As part of the Atmospheric Pollution and Human Health in a Chinese Megacity (APHH-Beijing) programme, we collected airborne particles at an urban site (Beijing) and an upwind rural site (Gucheng, Hebei province) in the NCP during 13–27 Nov. 2016 for microscopic analyses. We confirmed that large amounts of light-absorbing spherical POA (i.e., tarball) and irregular POA particles with high viscosity were emitted from the domestic coal and biomass burning at the rural site and were further transported to the urban site during regional wintertime hazes. During the heavily polluted period (PM2.5 > 200 μg m−3), more than 60% of these burning-related POA particles were thickly coated with secondary inorganic aerosols (named as core–shell POA–SIA particle) through the aging process, suggesting that POA particles can provide surfaces for the heterogeneous reactions of SO2 and NOx. As a result, their average particle-to-core diameter ratios at the rural and urban sites in the heavily polluted period increased to 1.60 and 1.67, respectively. Interestingly, we found that the aging process did not change the morphology and sizes of POA cores, indicating that these POA particles are quite inert in the atmosphere and can be transported long distances. Using Mie theory we estimated that the absorption capacity of POA particles was enhanced by ~1.39 times in the heavily polluted period at the rural and urban sites due to the “lensing effect” of secondary inorganic coatings. We highlight that the “lensing effect” on burning-related POA particles should be considered in radiative forcing models and the governments should continue to promote clean energy in rural areas to effectively reduce primary emissions.
How to cite: Liu, L., Zhang, J., and Li, W.: Persistent residential burning-related primary organic particles during wintertime hazes in North China: insights into their aging and optical changes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3796, https://doi.org/10.5194/egusphere-egu21-3796, 2021.
Size-dependent solubility is prevalent in atmospheric nanoparticles, but a molecular level understanding is still insufficient, especially for organic compounds. Here, we performed molecular dynamics simulations to investigate the size dependence of succinic acid solvation on the scale of ~1-4 nm with the potential of mean forces method. Our analyses reveal that the surface preference of succinic acid is stronger for a droplet than the slab of the same size, and the surface propensity is enhanced due to the curvature effect as the droplet becomes smaller. Energetic analyses show that such surface preference is primarily an enthalpic effect in both systems, while the entropic effect further enhances the surface propensity in droplets. On the other hand, with decreasing droplet size, the solubility of succinic acid in the internal bulk volume may decrease, imposing an opposite effect on the size dependence of solubility as compared with the enhanced surface propensity. Meanwhile, structural analyses, however, show that the surface to internal bulk volume ratio increases drastically, especially when considering the surface in respect to succinic acid, e.g., for droplet with radius of 1 nm, the internal bulk volume would be already close to zero for the succinic acid molecule.
How to cite: Chen, C., Wang, X., Binder, K., Ghahremanpour, M. M., van der Spoel, D., Pöschl, U., Su, H., and Cheng, Y.: Energetic analysis of succinic acid in water droplets: insight into the size-dependent solubility of atmospheric nanoparticles, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6415, https://doi.org/10.5194/egusphere-egu21-6415, 2021.
Despite the importance of aerosols in atmospheric chemistry, climate and air pollution, our ability to assess the impact of aerosols on atmospheric physics and chemistry is still limited due to insufficient understanding of many processes associated with sources of particles, their chemical composition and morphology, and evolution of their composition and properties during their atmospheric lifetime. Indeed, atmospheric aerosols can be viewed as a complex conglomerate of thousands of chemical compounds forming a system that evolves in the atmosphere by chemical and dynamical processing including chemical interaction with oxidants.
Multiphase processes have also been shown to produce light absorbing compounds in the particle phase. The formation of such light absorbing species could induce new photochemical processes within the aerosol particles and/or at the gas/particle interface. A significant body of literature on photo-induced charge or energy transfer in organic molecules from other fields of science (biochemistry and water waste treatment) exists. Such organic molecules are aromatics, substituted carbonyls and/or nitrogen containing compounds – all ubiquitous in tropospheric aerosols. Therefore, while aquatic photochemistry has recognized several of these processes that accelerate degradation of dissolved organic matter, only little is known about such processes in/on atmospheric particles.
This presentation will discuss photosensitization in the troposphere as having a significant role in SOA formation and ageing as studied by means of laser transient absorption spectroscopy, flow tube and simulation chamber experiments, all coupled to advanced analytical techniques. We will provide kinetic and mechanistic information on how photosensitization may introduce new chemical pathways, so far unconsidered, which can impact both the chemical composition of the atmosphere and might thus contribute to close the current SOA underestimation.
How to cite: George, C.: Photosensitization is in the air and impacts SOA generation and properties, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9393, https://doi.org/10.5194/egusphere-egu21-9393, 2021.
This study aims at comparing the gas-to-particle conversion mechanisms adopted by regional chemical transport models (CTMs). We use the results from twelve regional CTMs from the third phase of the Model Inter-Comparison Study for Asia (MICS-Asia III). The simulations are conducted over East Asia for the whole year of 2010. The models used are WRF-CMAQ (version 4.7.1 and v5.0.2), WRF-Chem (v3.6.1 and v3.7.1), GEOS-Chem, NHM-Chem, NAQPMS and NU-WRF. Measurements from 54 EANET sites, 86 sites of the Air Pollution Indices (API) and 35 local sites, remote sensing products from AERONET and satellite data from MODIS are used to evaluate model performance on PM10, PM2.5 and its components and aerosol optical depth (AOD). To investigate the inter-model differences in secondary aerosol formation, we compare the Sulfur Oxidation Ratio (SOR) and Nitrogen Oxidation Ratio (NOR) values by different models with observations at the EANET sites. The preliminary results show that the inter-model differences in the oxidation ratio (50%) are almost of the same magnitude as those in simulating the concentrations of particles. The results suggest large uncertainties in the gas-particle conversion process in modelling secondary aerosol formation.
How to cite: Tan, J., Fu, J., Carmichael, G., Su, H., and Cheng, Y.: Results on an Inter-model Comparison on Secondary Aerosol Formation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11154, https://doi.org/10.5194/egusphere-egu21-11154, 2021.
Ammonium salts (NH4+) is the important component of PM2.5 and has a significant impact on air quality, climate, human health, and natural ecosystems. The contribution of NH4+ to PM2.5 is increasing at urban sites. Ammonia (NH3) with global emissions estimated at greater than 33 Tg(N) Yr-1 is the only precursor of particulate NH4+ in the atmosphere. Thus, it is important to understand the conversion kinetics from NH3 to NH4+ in the atmosphere. However, the uptake coefficient of NH3 (γNH3) on aerosol particles are scarce at the present time. In this work, we reported the γNH3 on ambient PM2.5 in Beijing and Shijiazhuang in China. The γNH3 values on ambient PM2.5 are (1.13±12.4)×10-4 and (6.88±40.7)×10-4 in Shijiazhuang and Beijing, respectively. They are significantly lower than those on sulfuric acid droplet (0.1-1), aqueous surface (~5×10-3-0.1) and acidified secondary organic aerosol (~10-3-~10-2), while are comparable with that on ice surface (5.3±2.2 ×10-4) and on sulfuric acid in the presence of organic gases (2×10-4-4×10-3). An annual increase of γNH3 in the statistic sense is observed and the possible reason related to the aerosol acidity has also been discussed.
How to cite: Liu, Y., Feng, Z., Zhan, J., and Bao, X.: Heterogeneous uptake of NH3 on ambient PM2.5 in Beijing and Shijiazhuang: Possible influence of aerosol acidity, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8105, https://doi.org/10.5194/egusphere-egu21-8105, 2021.
Organic aerosols (OA) are major components of fine particulate matter, yet their formation mechanism remains unclear, especially in polluted environments. Laboratory studies have shown that the OA formation processes may be different under irradiated and dark conditions, but few studies have explored this aspect in ambient air. Here we investigate the diurnal chemical composition and formation processes of OA in carbonaceous particles during winter in Beijing using aerosol time-of-flight mass spectrometry. Our results show that 84.5% of carbonaceous particles undergo aging processes, characterized with larger size and more secondary species compared to fresh carbonaceous particles, and present different chemical compositions of OA in the daytime and nighttime. During the day, organosulfates and oligomers exist in the aged carbonaceous particles, which are mixed with a higher abundance of nitrate compared with sulfate. At night, distinct spectral signatures of hydroxymethanesulfonate and organic nitrogen compounds, and a minor abundance of other hydroxyalkylsulfonates and high molecular weight organic compounds are present in the aged carbonaceous particles, which are mixed with a higher abundance of sulfate compared with nitrate. Our results indicate that photochemistry dominates the formation of OA under high oxidant concentrations in the daytime, while aqueous chemistry plays an important role in the formation of OA under high relative humidity in the nighttime. The findings can help improve the performance of air quality and climate models on OA simulation.
How to cite: Ma, T., Furutani, H., Duan, F., Kimoto, T., Ma, Y., Zhu, L., Huang, T., Toyoda, M., and He, K.: Distinct diurnal formation processes of organic aerosols in winter in Beijing, China, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15866, https://doi.org/10.5194/egusphere-egu21-15866, 2021.
Snow acts as efficient scavenger of the ambient contaminants, bringing considerable amounts of dissolved organic matter (DOM) from the atmosphere to the freshwater and marine environments. Low molecular weight organic acids are important and ubiquitous chemical constituents in the atmosphere. However, very limited studies so far focused on the distributions of these organic compounds in snow. To investigate the spatial and molecular distributions in snow DOM over North China, twelve fresh snow samples were collected at eight sites including urban, rural and Changdao Island during January-February 2019. The snow samples were analyzed for dicarboxylic acids and related compounds together with dissolved organic carbon (DOC). The DOC concentrations ranged from 0.99 to 14.6 mgC L−1 in melt snow, which exhibited considerable spatial variation that was affected by terrestrial/anthropogenic inputs. Total diacids were very abundant varing from 225 to 1970 μg L−1, whereas oxoacids (28.3–173 μg L−1) and a-dicarbonyls (12.6–69.2 μg L−1) were less abundant. Molecular distributions of diacids were characterized by the predominance of oxalic acid (C2, 95.0–1030 μg L−1). Contrary to the results of other studies, the second largest amount of diacid in the snow samples showed a distinct spatial variation. Higher concentrations of phthalic acids (Ph) in snow samples in Tianjin and Beijing than those in other urban and rural regions suggest significant emissions from vehicular exhausts and incomplete combustion of fossil fuels in megacities. Glyoxylic acid (15.4–116 μg L−1) was the major oxoacids while methylglyoxal (MeGly) was the major a-dicarbonyl. The mass concentration ratio of C9 to total diacids was found to be highest in Changdao Island, indicating a significant input of marine derived unsaturated fatty acids such as oleic acid. These spatial distributions are consistent with photochemical production and the subsequent accumulation under different meteorological conditions. C2 diacid constituted 40–54% of total diacids, corresponding to 1.5–2.6% of snow DOC. The total measured water-soluble organic components represent 5.5–10% of snow DOC, which suggests that there are large amounts of unknown organics that need further investigations.
How to cite: Zhang, Z., Kawamura, K., and Fu, P.: Spatial and molecular distributions of dicarboxylic acids, oxocarboxylic acids, and a-dicarbonyls in snow in China, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6897, https://doi.org/10.5194/egusphere-egu21-6897, 2021.
Organic aerosol (OA) has been considered as one of the most important uncertainties in climate modeling due to the complexity in presenting its chemical production and depletion mechanisms. To better understand the capability of climate models and probe into the associated uncertainties in simulating OA, we evaluate the Community Earth System Model version 2.1 (CESM2.1) configured with the Community Atmosphere Model version 6 (CAM6) with comprehensive tropospheric and stratospheric chemistry representation (CAM6-Chem), through a long-term simulation (1988–2019) with observations collected from multiple datasets in the United States. We find that CESM generally reproduces the inter-annual variation and seasonal cycle of OA mass concentration at surface layer with correlation of 0.40 as compared to ground observations, and systematically overestimates (69 %) in summer and underestimates (-19 %) in winter. Through a series of sensitivity simulations, we reveal that modeling bias is primarily related to the dominant fraction of monoterpene-formed secondary organic aerosol (SOA), and a strong positive correlation of 0.67 is found between monoterpene emission and modeling bias in eastern US during summer. In terms of vertical profile, the model prominently underestimates OA and monoterpene concentrations by 37–99 % and 82–99 % respectively in the upper air (>500 m) as validated against aircraft observations. Our study suggests that the current Volatility Basis Set (VBS) scheme applied in CESM might be parameterized with too high monoterpene SOA yields which subsequently result in strong SOA production near emission source area. We also find that the model has difficulty in reproducing the decreasing trend of surface OA in southeast US, probably because of employing pure gas VBS to represent isoprene SOA which is in reality mainly formed through multiphase chemistry, thus the influence of aerosol acidity and sulfate particle change on isoprene SOA formation has not been fully considered in the model. This study reveals the urgent need to improve the SOA modeling in climate models.
How to cite: Liu, Y., Dong, X., Wang, M., Emmons, L., Liu, Y., Liang, Y., Li, X., and Shrivastava, M.: Analysis of Secondary Organic Aerosol Simulation Bias in the Community Earth System Model (CESM2.1), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1915, https://doi.org/10.5194/egusphere-egu21-1915, 2021.
Nitrated phenols in the atmosphere are receiving increasing attentions due to their light absorption and biological toxicity. However, the partitioning characteristics of nitrated phenols among gas, particle, and aqueous phases and the dominant influencing factors remain unclear. In this work, particulate, gaseous, and cloud water samples were simultaneously collected at the summit of Mt. Tai in North China in spring, summer and winter. The contents of 11 nitrated phenols in these samples were determined with an ultra-high-performance liquid chromatograph in tandem with a mass spectrometer. The total concentrations of nitrated phenols in PM2.5 were in the range of several to dozens of ng m-3, a little lower than those measured in gas phase. The total concentrations of nitrated phenols in cloud water were in the level of hundreds of µg L-1. Among the 11 nitrated phenols, 4-nitrophenol and nitrosalicylic acids were the most dominant compounds in PM2.5, while 4-nitrophenol and 2,4-dinitrophenol were the most abundant in gas-phase and cloud water samples. During cloud events, most nitrated phenols were mainly distributed in particle phase, except dinitrophenols which were mainly distributed in gas phase. The observed concentration ratios of aqueous nitrated phenols to those in gas phase were one to two orders higher than the theoretical Henry’s law coefficients in pure water. Moreover, the measured concentrations of particulate nitrated phenols were substantially greater than the theoretically predicted values. The above results indicate that nitrated phenols potentially formed via aqueous-phase reactions inside the cloud droplets or on the surface of particles. The much higher ratios of the sum of 4-nitrophenol and 5-nitrosalicylic acid to 2,4-dinitrophenol in cloud water than those in PM2.5 further confirms the enhanced formation via aqueous processes. Overall, aqueous-phase reactions were important sources of atmospheric nitrated phenols during cloud events and had significant influences on the abundance and distributions of nitrated phenols in different phases.
How to cite: Wang, X., Li, M., Zhao, Y., Du, P., Liu, Z., Li, H., Shen, H., Xue, L., Wang, Y., Chen, J., and Wang, W.: Atmospheric nitrated phenols at a mountain site in North China: compositions, phase partitioning, and aqueous formation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9395, https://doi.org/10.5194/egusphere-egu21-9395, 2021.
To reveal the characteristics of aerosols in polluted environments, we measured aerosol number size distributions in the size range of ~1 nm – 10 μm during 2018- 2020 in urban Beijing. As a vital process influencing the aerosol size distributions, new particle formation (NPF) events were frequently observed in urban Beijing. We classified NPF days into typical NPF days with a burst of sub‑3 nm particles and those with few sub‑3 nm particles. We examined their characteristics and possible reasons. The mean aerosol number size distributions were clearly different and the peak particle diameter was ~1.5 nm and 12 nm, respectively. For those with a burst of sub-3 nm particles, however, the peak diameter shifts from small diameter to larger particle diameters as the aerosol size distribution evolves during the NPF process and then becomes similar to those with few sub-3 nm particles. Meteorological analysis indicates that airmass movement may account for these observations. Despite these differences, similar diurnal patterns were observed on most days in urban Beijing, i.e., drastic change in aerosol size distributions happens around 4:00 a.m. and 4:00 p.m.
How to cite: Deng, C., Li, Y., Chen, X., and Jiang, J.: Long-term aerosol number size distributions down to 1 nm in urban Beijing, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11642, https://doi.org/10.5194/egusphere-egu21-11642, 2021.
Secondary new particle formation is an important source of the number concentration of atmospheric aerosols. Despite relatively high coagulation sinks contributed by pre-existing aerosols, intensive new particle formation occurs frequently in polluted atmospheric environments such as in urban Beijing. Considering the measured concentrations of sulfuric acid and organic compounds, the contrast between the high coagulation sink and the frequent intensive NPF events in urban Beijing indicates an efficient nucleation mechanism. Based on long-term atmospheric measurements conducted at the campus of Beijing University of Chemical Technology, we show that sulfuric acid-amine nucleation is a governing mechanism to initiate new particle formation in urban Beijing. The molecular-level mechanism of sulfuric acid-amine nucleation, especially with low amine concentrations and high aerosol concentrations, are discussed. We present evidence for the existence of the missing amine molecules in the measured H2SO4-amine clusters. A neutral cluster needs to be ionized before it is detected by a mass spectrometer. Deprotonation or clustering with an additional reagent ion changes the stability of the original neutral cluster. Therefore, the amine molecules in neutral H2SO4-amine clusters may dissociate before detection. Combining measurements and cluster kinetic simulations, we show that although not directly detected, a considerable proportion of H2SO4 monomers exist in the form of (H2SO4)1(amine)1, where the amine is most likely to be dimethylamine or trimethylamine. The evaporation rate of (H2SO4)1(amine)1 is moderate and forming (H2SO4)1(amine)1 is a critical step for H2SO4-amine nucleation. According to nucleation theory, (H2SO4)1(amine)1 is the critical cluster at a low amine concentration, whereas H2SO4-amine nucleation may occur without a free energy barrier at a high amine concentration. The clustering between (H2SO4)1(amine)1 and (H2SO4)n(amine)n is a major reaction pathway for the initial growth of H2SO4-amine clusters. These findings are supported by the measured H2SO4 dimer concentration and its dependencies on amine concentrations and temperature in urban Beijing. Besides, the enhancement of cluster growth rate due to synergy between amines and ammonia are discussed.
How to cite: Cai, R., Yan, C., Zheng, J., Wang, L., Kulmala, M., and Jingkun, J.: Secondary new particle formation initiated by sulfuric acid-amine nucleation in Beijing, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9729, https://doi.org/10.5194/egusphere-egu21-9729, 2021.
Ultrafine particles (UFPs) dominate the particle number population in the urban atmosphere and revealing their chemical composition is important. The thermal desorption chemical ionization mass spectrometer (TDCIMS) can semi-continuously measure UFP composition at the molecular level. We modified a TDCIMS and deployed it in urban Beijing. Radioactive materials in the TDCIMS for aerosol charging and chemical ionization were replaced by soft X-ray ionizers so that it can be operated in countries with tight regulations on radioactive materials. Protonated N-methyl-2-pyrrolidone ions were used as the positive reagent ion, which selectively detects ammonia and low-molecular weight-aliphatic amines and amides vaporized from the particle phase. With superoxide as the negative reagent ion, a wide range of inorganic and organic compounds were observed, including nitrate, sulfate, aliphatic acids with carbon numbers up to 18, and highly oxygenated CHO, CHON, and CHOS compounds. The latter two can be attributed to parent ions or the decomposition products of organonitrates and organosulfates/organosulfonates, respectively. Components from both primary emissions and secondary formation of UFPs were identified. Compared to the UFPs measured at forest and marine sites, those in urban Beijing contain more nitrogen-containing and sulfur-containing compounds. These observations illustrate unique features of the UFPs in this polluted urban environment and provide insights into their origins.
How to cite: Li, X., Li, Y., Lawler, M., Hao, J., Smith, J., and Jiang, J.: Composition of ultrafine particles in urban Beijing: Measurement using a thermal desorption chemical ionization mass spectrometer, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11971, https://doi.org/10.5194/egusphere-egu21-11971, 2021.
The formation of secondary aerosols (SA, including secondary organic and inorganic aerosols, SOA and SIA) were the dominant sources of aerosol particles in the North China Plain and can result in significant variations of particle size distribution (PNSD) and hygroscopicity. Earlier studies have shown that the mechanism of SA formation can be affected by relative humidity (RH), and thus has different influences on the aerosol hygroscopicity and PNSD under different RH conditions. Based on the measurements of size-resolved particle activation ratio (SPAR), hygroscopicity distribution (GF-PDF), PM2.5 chemical composition, PNSD, meteorology and gaseous pollutants in a recent field campaign McFAN (Multiphase chemistry experiment in Fogs and Aerosols in the North China Plain) conducted at Gucheng site from November 16th to December 16th in 2018, the influences of SA formation on CCN activity and CCN number concentration (NCCN) calculation at super-saturation of 0.05% under different RH conditions were studied. Measurements showed that during daytime, SA formation could lead to a significant increase in NCCN and a strong diurnal variation in CCN activity. During periods with daytime minimum RH exceeding 50% (high RH conditions), SA formation significantly contributed to the particle mass/size changes in wide particle size range of 150 nm to 1000 nm, and led to an increase of NCCN in particle size range of 200 nm to 300 nm, while increases in particle mass concentration mainly occurred within particle sizes larger than 300nm. During periods with daytime minimum RH below 30% in (low RH conditions), SA formation mainly contributed to the particle mass/size and NCCN changes in particle sizes smaller than 300 nm. As a result, under the same amount SA formation induced mass increase, the increase of NCCN was weaker under high RH conditions, while stronger under low RH conditions. Moreover, the diurnal variations of aerosol mixing state (inferred from CCN measurements) due to SA formation was different under different RH conditions. If the variations of the aerosol mixing state were not considered, estimations of NCCN would bear significant deviations. By applying aerosol mixing state estimated by number fraction of hygroscopic particles from measurements of particle hygroscopicity or mass fraction of SA from measurements of particle chemical compositions, NCCN calculation can be largely improved with relative deviation within 30%. This study improves the understanding of the impact of SA formation on CCN activity and NCCN calculation, which is of great significance for improving parameterization of SA formation in aerosol models and CCN calculation in climate models.
How to cite: Tao, J., Kuang, Y., Ma, N., Hong, J., Sun, Y., Xu, W., Zhang, Y., He, Y., Luo, Q., Xie, L., Su, H., and Cheng, Y.: Secondary aerosol formation alters CCN activity in the North China Plain, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11204, https://doi.org/10.5194/egusphere-egu21-11204, 2021.
PM2.5 is considered to be the most dangerous form of air pollution and is formed of a complex mixture of both primary and secondary species, from both biogenic and anthropogenic sources. Organic aerosol, comprised of modern carbon has been shown to dominate even in urban settings, but sources and formation mechanism of these biogenic aerosol in the ambient atmosphere remain uncertain. The collection and offline analysis of PM2.5 aerosol samples allows for highly detailed molecular level compositional information to be obtained, but at the cost of time resolution. Previous studies have collected 23-hour offline filters, which although allowing for seasonal changes to be studied, cannot resolve diurnal variations. However, due to recent advances in high-resolution mass spectrometers, the time resolution of offline filters can now be increased. This study utilises high time resolution offline filters collected in Guangzhou, China across two campaigns during summer and winter. Filters were collected every 2 hours during the day (06:00 – 21:00), with a longer collection overnight (21:00-06:00), alongside a suite of complementary gas phase measurements. Guangzhou represents an interesting case study for biogenic secondary organic aerosol (BSOA) especially biogenic-anthropogenic interactions due to its tropical location and high levels of flora, but also located in one of the most densely populated regions of the world within the Guangdong-Hong Kong-Macau Greater Bay area, with a combined population of 71.2 million people.
This study presents ultra-high-performance liquid chromatography, high-resolution mass spectrometry measurements of BSOA tracers identified in the ambient PM2.5 samples at the highest time resolution studied so far. A library of 180 potential BSOA tracers from isoprene, monoterpenes and sesquiterpenes was developed containing acid species (CHO), organosulfates (CHOS) and nitrooxy organosulfates (CHOSN). The BSOA tracers were quantified using a mixture of authentic standards, proxy standards and modelled RIE factors for accurate quantification. Matrix suppression factors were also determined for both CHO and CHOS/CHOSN species, splitting the compounds into groups based on their retention time (RT), with species eluting before 2 min showing the largest matrix suppression.
Strong diurnal variations were observed for some species while others showed little or no diurnal variation suggesting nonlocal sources, and as such provides insight into how long-range sources can affect BSOA concentrations. Tracers were also correlated to anthropogenic pollutants such as NOX and SO2 as well as sulfate and nitrate measured via ion chromatography, improving our understanding of biogenic-anthropogenic interactions. Comparisons between summer and winter allowed insight into seasonal processes and concentrations, with the potential for different long-range sources. Finally, this study presents comparisons to a growing field of offline BSOA measurements, providing a more comprehensive picture of the contributions BSOA makes to PM2.5 concentrations.
How to cite: Bryant, D., Elzein, A., Newland, M., White, E., Watkins, A., Pereira, K., Deng, W., Song, W., Wang, S., Wang, X., Rickard, A., and Hamilton, J.: High time resolution offline analysis of biogenic secondary organic aerosol in Guangzhou, China., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12291, https://doi.org/10.5194/egusphere-egu21-12291, 2021.
Organic aerosols (OA) that make up a large fraction (up to 90%) of the fine aerosol (PM2.5) mass have severe impact on the Earth’s climate system and can cause adverse risk to human health. Diacids and related compounds are ubiquitous in PM2.5 in different environments and accounts for a substantial fraction in OA. Because of their high water-solubility, they can influence the hygroscopic properties and capacity of cloud condensation nuclei formation activity of aerosols and thus affect the indirect radiative forcing in the atmosphere. However, their origins, secondary formation and transformations and seasonality are not fully understood yet. To better understand the seasonal characteristics, origins and photochemical processing of OA in the Tianjin region, North China, we studied the molecular distributions and seasonal variations of water-soluble diacids, oxoacids and α-dicarbonyls in PM2.5 collected at an urban and a suburban sites in Tianjin, an ideal location to study the aerosols, over a one-year period from July 2018 to June 2019. We found significant changes in concentrations and composition of diacids and related compounds from season to season at both the sites. Here, based on the results obtained together with the meteorology, oxidants (O3 and NO2) and SO2, loading and the backward air mass trajectories, we discuss the possible origins and possible secondary formation pathways of diacids and related compounds in the Tianjin region.
How to cite: Li, P., Pavuluri, C. M., Dong, Z., Xu, Z., Fu, P., and Liu, C.-Q.: Seasonal Changes in Molecular Distributions of Diacids, Oxoacids and α-Dicarbonyls in PM2.5 in Tianjin, North China: Implications for Origins and Secondary Formation Pathways in Cold and Warm Periods, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13804, https://doi.org/10.5194/egusphere-egu21-13804, 2021.
Hygroscopic properties of 23 organic compounds with different physico-chemical properties including carboxylic acids, amino acids, sugars and sugar alcohols were measured using a Hygroscopicity Tandem Differential Mobility Analyzer (HTDMA). We converted our experimental GF data of organics at 90% RH to κ to facilitate the comparison and we find that organic compounds with different molecular functionality present quite different hygroscopicity. Compounds with extra functional groups usually show higher hygroscopicity compared to their parental molecular compounds. Moreover, some compounds share the same molecular structure or functionality but vary differently in hygroscopicity. In general, the hygroscopicity of organics increase with functional groups in the following order: (-CH3/-NH2) < (-OH) < (-COOH/C=C/C=O). For highly soluble organics, the hygroscopicity decreases with molecular weight; while for slightly soluble organics which are not fully dissolved in aerosol droplets, their hygroscopicity can be divided into two categories. One is non-hygroscopic compounds, which may not fully deliquesce in the aerosol droplets. The other is moderate hygroscopic compounds, of which the hygroscopicity is mainly limited by their water solubility. Moreover, the hygroscopicity of organic compounds generally increased linearly with O:C ratios, although some of them have the same O:C ratio of but with different hygroscopicity. The experimental determined hygroscopicity are also compared with model predictions using the Extended Aerosol Inorganics Model (E-AIM) and the UManSysProp at 10-90% RH. Both models poorly represent the hygroscopic behavior of some organics, which may due to that the phase transition and intermolecular interactions are not considered in the simulations.
How to cite: han, S., Hong, J., Luo, Q., Xu, H., Tan, H., Wang, Q., Tao, J., Ma, N., Cheng, Y., and Su, H.: Hygroscopicity of organic compounds as a function of organic functionality, water solubility, molecular weight and organic oxidation level, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13985, https://doi.org/10.5194/egusphere-egu21-13985, 2021.
Vertical measurements of aerosol physical-chemical properties have important significance for better addressing the environment and climate effects of atmospheric aerosol. Traditional in-situ vertical observations of those properties are mainly based on aircraft platforms which are costly and restrictive, and not applicable for near-ground (<500 m) measurements. Within the boundary layer, tethered balloon and unmanned aerial vehicle (UAV) are ideal observation platforms but cannot carry heavy online aerosol instruments due to payload limitations. In this study, a new lightweight airborne aerosol sampling system is developed for tethered balloon and UAV platform. The system can collect airborne aerosol samples at up to 12 heights with conductive bags, and the samples can be analyzed later by online instruments such as aerosol mass spectrometer and single particle soot photometer (SP2). During an intensive field campaign conducted in Lhasa in summer of 2020, the new developed system was applied together with a SP2 to determine the vertical profile of refractory black carbon (rBC) mixing state. Preliminary results show that most rBC containing particles are external mixture and the proportion of internally mixed rBC increases with height. The vertical profiles of rBC mixing state are affected by surface emissions, the development of atmospheric boundary layer and meteorological conditions.
How to cite: Zhu, S., Ma, N., Xie, L., Lu, N., Li, M., Chen, S., Mao, J., Yu, P., Deng, Z., Ran, L., Su, H., and Cheng, Y.: A new airborne aerosol sampling system: development, validation, and application in vertical measurement of black carbon mixing state, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7467, https://doi.org/10.5194/egusphere-egu21-7467, 2021.
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