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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".

Public information:
Session invited talk (live presentations on Zoom Meetings):

Mon, 04 May, 14:00-15:45 (Vienna Time)

14:00-14:35 Markku Kulmala, Reducing urban new particle formation as a plausible solution to
mitigate particulate air pollution in Beijing and other Chinese megacities
14:35-15:10 Gregory Carmichael, Aerosol Chemistry and Effects in the Anthropocene
15:10-15:45 Meng Gao, Aerosol Pollution in Asia and Its Interactions with Climate

Join Zoom Meeting: https://zoom.us/j/8425924612
Meeting ID: 842 592 4612
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Convener: Yafang Cheng | Co-conveners: Pingqing Fu, Jingkun Jiang, Nan MaECSECS, Hang Su
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| Attendance Mon, 04 May, 14:00–15:45 (CEST)

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Chat time: Monday, 4 May 2020, 14:00–15:45

D3574 |
EGU2020-10308
| Highlight
Markku Kulmala, Lubna Dada, Federico Bianchi, and Chao Yan and the Aerosol and Haze Laboratory Team

With multi- and interdisciplinary approaches we show that atmospheric secondary particles are the dominating contributor to haze formation in terms of aerosol number, surface area and mass. Supported by our comprehensive observations in Beijing during 15 January 2018– 15 January 2020, we show that 80–90% of the aerosol mass (PM2.5) was formed via atmospheric reactions during the haze days and over 65% of the number concentration of haze particles resulted from urban new particle formation (NPF). Furthermore, the haze formation was much faster when the subsequent growth of newly formed particles was enhanced (rapid growth). We found that since the direct emissions of primary particles in Beijing has gone down significantly within recent years, all present-day haze episodes we preceded by a urban NPF event. We are also able to show that reducing the subsequent growth of freshly formed particles by a factor of 3-5 would delay the buildup of haze episodes by 1–3 days. Actually, this delay will decrease the length of each haze episode and the number of annual haze days could be approximately halved. The improvement can be achieved with targeted reduction of NPF precursors, mainly dimethyl amine, ammonia and further reductions of SO2 emissions. Furthermore, reduction of anthropogenic VOC and nitrate emissions will slow down the growth rate of newly-formed particles and consequently reduce the haze formation. Our results show that the presence of haze decreases both boundary layer height and urban heat island intensity, which will further enhance haze particle number and mass concentrations over large spatial scales.

 

How to cite: Kulmala, M., Dada, L., Bianchi, F., and Yan, C. and the Aerosol and Haze Laboratory Team: Reducing urban new particle formation as a plausible solution to mitigate particulate air pollution in Beijing and other Chinese megacities , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10308, https://doi.org/10.5194/egusphere-egu2020-10308, 2020

D3575 |
EGU2020-8262
Runlong Cai, Chao Yan, Jun Zheng, Lin Wang, Markku Kulmala, and Jingkun Jiang

The formation of new secondary aerosols form gaseous precursors is a frequent phenomenon in various atmospheric environments and it impacts aerosol number concentration, cloud formation, and hence climate. There has been a considerable number of new particle formation (NPF) studies in various atmospheric environments, but current knowledge on NPF in the polluted atmospheric boundary layer (e.g., the urban environment in megacities) is still limited. The clustering of H2SO4 and amines is a possible mechanism driving the fast nucleation and initial growth of new particles in the polluted urban environment. Laboratory studies using typical ambient H2SO4 concentrations and theoretical calculations based on quantum chemistry have provided insights into H2SO4-amine nucleation. However, the molecular-level mechanism and governing factors for H2SO4-amine nucleation have not been quantitatively investigated in the real atmosphere. Some previous studies indicate that differently from clean environments, the coagulation scavenging is a governing factor for NPF in polluted environments. In the presence of a high aerosol concentration in the polluted environment, a considerable fraction of the newly formed particles are scavenged by coagulation within minutes and hence, NPF is significantly suppressed. Similarly, the coagulation scavenging may also impact the steady-state cluster concentrations and the new particle formation rate. Due to the differences in the coagulation scavenging and perhaps some gaseous precursor concentrations between laboratory and atmospheric conditions, the reaction kinetics determined in previous laboratory studies may not directly applicable to the real atmosphere. Herein, based on long-term atmospheric measurements from January 2018 to March 2019 in urban Beijing, we show the different reaction kinetics under laboratory and atmospheric conditions and how to unify them using proper normalization approaches. The influences of governing factors on particle formation rate are then quantitatively elucidated. Based on the synergistic effects of these factors, an indicator for the occurrence of NPF in the urban environment is proposed and verified.

How to cite: Cai, R., Yan, C., Zheng, J., Wang, L., Kulmala, M., and Jiang, J.: Kinetics of sulfuric acid-amine nucleation in the urban atmospheric environment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8262, https://doi.org/10.5194/egusphere-egu2020-8262, 2020

D3576 |
EGU2020-7948
Chemical Mixing State of Urban Haze Particles
(withdrawn)
Zhijun Wu, Yishu Zhu, Peter Alpert, Jing Dou, Taomou Zong, Song Guo, Ulrich K. Krieger, Markus Ammann, and Min Hu
D3577 |
EGU2020-18043
Xihao Pan, Nan Ma, Yaqing Zhou, Shaowen Zhu, Long Peng, Guo Li, Yuxuan Zhang, Jiangchuan Tao, Xinhui Bi, Qiang Zhang, Hang Su, and Yafang Cheng

Black carbon (BC) is the most important light-absorbing species in the atmosphere and has a strong positive direct radiative forcing. In-cloud scavenging is the major way to wash out BC from the atmosphere. Understanding the connection between its physico-chemical properties and scavenging efficiency is therefore a key to evaluate its lifetime, atmospheric burden and spatial distribution. During an intensive field campaign conducted in the North China Plain in 2019, a ground-based counterflow virtual impactor was utilized to separate fog droplets in radiation fog events. BC mass and mixing state of fog droplet residues were online measured with a single particle soot photometer (SP2). In a strong radiation fog event with visibility of about 50 m, more than 20% fog droplets are found to contain a BC core. BC scavenging efficiency is found to be strongly determined by its diameter and mixing state. Driven by different mechanisms, higher scavenging efficiencies up to 10% are observed for larger and smaller BC particles, and the minimum efficiency is found at BC diameter of 120 nm. For large core (>120 nm) BC-containing particles, the scavenging efficiency increases significantly with coating thickness (CT), from about 10% for CT<100 nm to 80% for CT>300 nm. Chemical composition may also be a key parameter influencing the scavenging of BC. Based on the observation of 3 fog events, parameterizations of BC scavenging efficiency are also given in this study.

How to cite: Pan, X., Ma, N., Zhou, Y., Zhu, S., Peng, L., Li, G., Zhang, Y., Tao, J., Bi, X., Zhang, Q., Su, H., and Cheng, Y.: Influence of size and mixing state on the wet scavenging of black carbon aerosol in the North China Plain, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18043, https://doi.org/10.5194/egusphere-egu2020-18043, 2020

D3578 |
EGU2020-7
Mingjin Tang, Huanhuan Zhang, and Wenjun Gu

Saline mineral dust particles, emitted from saline topsoil in arid and semi-arid regions, contribute significantly to tropospheric aerosol particles. However, hygroscopic properties of saline mineral dust particles, especially for those found in regions other than North America, are poorly understood. In this work we investigated hygroscopic properties of thirteen saline mineral dust samples collected from different locations via measuring sample mass change as different relative humidity (RH, up to 90%), and measured their chemical and mineralogical compositions using ion chromatography and X-ray diffraction. The mass growth factors at 90% RH, defined as the sample mass at 90% RH relative to that at <1% RH, were found to display large geographical variations, spanning from ~1.02 to 6.7, and the corresponding single hygroscopicity parameters (κ) were derived to be in the range of <0.01 to >1.0. The saline components (mainly Na+, Cl- and SO42-) contained by saline mineral dust particles largely determined their hygroscopicity, and the predicted mass growth factors at 90% RH using an aerosol thermodynamic model (ISORROPIA-II), agreed with measured values within 20% for most of samples examined, though larger discrepancies also occurred for three samples. Our results improve our understanding in hygroscopicity of saline mineral dust particles and thus their heterogeneous chemistry and ability to serve as cloud condensation nuclei to form cloud droplets.

How to cite: Tang, M., Zhang, H., and Gu, W.: Hygroscopic properties of saline mineral dust from different regions in China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7, https://doi.org/10.5194/egusphere-egu2020-7, 2019

D3579 |
EGU2020-12687
Shuang Han, Juan Hong, Hanbing Xu, Haobo Tan, Fei Li, Lin Wang, and Nan Ma

Volatility and hygroscopicity properties of atmospheric particles with dry sizes of 60 and 145 nm were measured by using a Volatility-Hygroscopicity Tandem Differential Mobility Analyzer (VH-TDMA) at a suburban site over the Pearl River Delta region in China during the late summer of 2016. Specifically, volatility properties of the aerosols were studied by heating the ambient samples step-wise to seven temperatures ranging from 30 to 300℃. In general, particles started to evaporate at the heating temperature of 100℃. After heating the aerosols above 200℃, the probability density function of the volatility growth factor showed an apparent bimodal distribution with a distinct non-volatile mode and a volatile mode, indicating that the particle population was mainly externally mixed. Even at 300℃, around 20% of the aerosol volume still remained in the particle phase (non-volatile material). Black carbon (BC) mass fraction of aerosol mass correlated well (R2≈ 0.5) with the volume fraction remaining (VFR) at 300℃, but could not explain the non-volatile residual alone. On the basis of the comparison analysis between the VFR at different temperatures and the hygroscopic growth factor (HGF) at 90% RH, we observed the non-volatile residual material were hygroscopic (HGF=1.45). These results indicate that the observed non-volatile residual material at 300℃ did not consist solely of black carbon, but some other compounds such as sea salt, low-volatile ammonium or organic polymer.

How to cite: Han, S., Hong, J., Xu, H., Tan, H., Li, F., Wang, L., and Ma, N.: Comparison of volatility, hygroscopicity and oxidation state of submicron aerosols over the Pearl River Delta region in China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12687, https://doi.org/10.5194/egusphere-egu2020-12687, 2020

D3580 |
EGU2020-2803
Jingyi Li, Qi Ying, and Jianlin Hu

Secondary organic aerosol (SOA) is an important component of fine particular matter (PM2.5) in China. Most air quality models use an equilibrium partitioning method along with estimated saturation vapor pressure of semi-volatile organic compounds (SVOCs) to predict SOA formation. However, this method ignores partitioning of water vapor to the organic aerosols and the organic phase non-ideality, both of which affect the partitioning of SVOCs. In this study, the Community Multi-scale Air Quality model (CMAQv5.0.1) was used to investigate the above impacts on SOA formation during winter (January) and summer (July) of 2013 over eastern China. The organic aerosol module was updated by incorporating water partitioning into the organic particulate matter (OPM) and considering non-ideality of organic-water mixture. The modified model can generally capture the observed organic carbon (OC), the total organic aerosol (OA) and diurnal variation of PM2.5 at ground sites. SOA concentration shows significant seasonal and spatial variations, with high concentration levels in North China Plain (NCP), Central China and Sichuan basin (SCB) areas during winter (up to 25 μg m-3) and in Yangtze River Delta (YRD) during summer (up to 12 μg m-3). When water partitioning is included in winter, SOA concentrations increase slightly, with the monthly-averaged daily maximum relative difference of 10-20% at the surface and 10-30% for the whole column, mostly due to the increase in anthropogenic SOA. The increase in SOA is more significant in summer, by 20-90% at the surface and 30-70% for the whole column. The increase of SOA over the land is mostly due to biogenic SOA while the increase of SOA over the coastal regions is related with that of anthropogenic origin. Further analysis of two representative cities, Jinan and Nanjing, shows that changes of SOA are favored under hot and humid conditions. The increases in SOA cause a 12% elevation in the aerosol optical depth (AOD) and 15% enhancement in the cooling effects of aerosol radiative forcing (ARF) over YRD in summer. The aerosol liquid water content associated with OPM (ALWorg) at the surface is relatively high over the land in winter and over the ocean in summer, with the monthly-averaged daily maximum of 2-9 and 5-12 μg m-3, respectively. By using the -Köhler theory, we calculated the hygroscopicity of OA with modeled ALWorg, finding that the correlation with O:C ratio varies significantly across different cities and seasons. Water partitioning into OPM only promotes SOA formation, while non-ideality of organic-water mixture only leads to decreases in SOA in most regions of eastern China. Water partitioning into OPM should be considered in air quality models in simulating SOA, especially in hot and humid environments.

How to cite: Li, J., Ying, Q., and Hu, J.: Impacts of water partitioning and polarity of organic compounds on secondary organic aerosol over Eastern China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2803, https://doi.org/10.5194/egusphere-egu2020-2803, 2020

D3581 |
EGU2020-1319
| Highlight
| AS Division Outstanding ECS Lecture
Meng Gao

With rapidly expanding economic and industrial developments and tremendous increases in energy consumption, China and India are facing serious aerosol pollution, posing great threat to human health. Aerosols also modulate the climate and ecosystems via aerosol-cloud-radiation interactions. Yet, the poor understanding of aerosol pollution in Asia and its interactions with climate impedes the design and implementation of effective pollution control measures. Combining atmospheric modeling and observations, we demonstrated that the aerosol interactions with radiation and clouds contributed in important ways to intensification of the aerosol enhancements in North China. We manifested also how assimilation of PM2.5 in winter haze periods can improve model predictions and that these improved predictions can reduce significantly the uncertainties in health impacts and estimates of aerosol radiative forcing. It was also demonstrated that the conditions of the ocean temperature in fall can be effectively used to predict the severity of Indian winter haze, which provides useful implications for pollution control at least a season in advance.

How to cite: Gao, M.: Aerosol Pollution in Asia and Its Interactions with Climate, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1319, https://doi.org/10.5194/egusphere-egu2020-1319, 2019

D3582 |
EGU2020-19687
| Highlight
Gregory Carmichael

Atmospheric aerosols impact air quality and human health. They also play a key role in the Earth’s weather and climate systems.  Aerosol amounts and physical and chemical properties determine their toxicity, radiative and microphysical impacts. Recent advances in observations and models are significantly enhancing our ability to quantify the distribution and properties of aerosols, understand their impacts on atmospheric radiation and cloud distributions and properties, and their presence near the Earth’s surface and the resulting impacts to human health. There is a need for closer integration of aerosols into numerical prediction systems. The World Meteorological Organization has set a strategic goal to advance earth systems modeling to enhance seamless prediction of environmental, weather and climate services across spatial and temporal scales. In this talk the need for this approach and the opportunities and advances will be discussed.

How to cite: Carmichael, G.: Aerosol Chemistry and Effects in the Anthropocene, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19687, https://doi.org/10.5194/egusphere-egu2020-19687, 2020

D3583 |
EGU2020-9793
Andreas Tilgner, Erik Hans Hoffmann, Lin He, Bernd Heinold, Can Ye, Yujing Mu, Hui Chen, Jianmin Chen, and Hartmut Herrmann

During winter, the North China Plain (NCP) is frequently characterized by severe haze conditions connected with extremely high PM2.5 and NOx concentrations, i.e. strong air pollution. The NCP is one of the most populated regions worldwide where haze periods have direct health effects. Tropospheric haze particles are a complex multiphase and multi-component environment, in which multiphase chemical processes are able to alter the chemical aerosol composition and deduced physical aerosol properties and can strongly contribute to air pollution. Despite many past investigations, the chemical haze processing is still uncertain and represents a challenge to atmospheric chemistry research. Recent NCP studies during autumn/winter 2017 haze periods have revealed unexpected high H2O2 concentrations of about 1 ppb suggesting H2O2 as a potential contributor to secondary PM2.5 mass, e.g., due to sulfur(IV) oxidation. However, the multiphase H2O2 formation under such NOx concentrations is still unclear. Therefore, the present study aimed at the examination of potential multiphase H2O2 formation pathways, and the feedback on sulfur oxidation.

Multiphase chemistry simulations of a measurement campaign in the NCP are performed with the box model SPACCIM. The multiphase chemistry model within SPACCIM contains the gas-phase mechanism MCMv3.2 and the aqueous-phase mechanism CAPRAM4.0 together with both its aromatics module CAPRAM-AM1.0 and its halogen module CAPRAM-HM2.1. Furthermore, based on available literature data, the multiphase chemistry mechanism is extended considering further multiphase formation pathways of HONO and an advanced HOx mechanism scheme enabling higher in-situ H2O2 formations in haze particles. The simulations have been performed for three periods characterized by high H2O2 concentrations, high RH and PM2.5 conditions and high measurement data availability. Several sensitivity runs have been performed examining the impact of the soluble transition metal ion (TMI) content on the predicted H2O2 formation.

Simulations with the improved multiphase chemistry mechanism shows a good agreement of the modelled H2O2 concentrations with field data. The modelled H2O2 concentration shows a substantial dependency on the soluble TMI content. Higher soluble TMI contents result in higher H2O2 concentrations demonstrating the strong influence of TMI chemistry in haze particles on H2O2 formation. The analysis of the chemical production and sink fluxes reveals that a huge fraction of the multiphase HO2 radicals and nearly all of the subsequently formed reaction product H2O2 is produced in-situ within the haze particles and does not origin from the gas phase. Further chemical analyses show that, during the morning hours, the aqueous-phase reaction of H2O2 with S(IV) contributes considerably to S(VI) formation beside the HONO related formation of sulfuric acid by OH in the gas-phase.

Finally, a parameterization was developed to study the particle-phase H2O2 formations as potential source with the global model ECHAM-HAMMOZ. The performed global modelling identifies an increase of gas-phase H2O2 by a factor of 2.8 through the newly identified particle chemistry. Overall, the study demonstrated that photochemical reactions of HULIS and TMIs in particles are an important H2O2 source leading to increased particle sulfate formation.

How to cite: Tilgner, A., Hoffmann, E. H., He, L., Heinold, B., Ye, C., Mu, Y., Chen, H., Chen, J., and Herrmann, H.: Modelling the photochemical formation of high H2O2 concentrations and secondary sulfate observed during winter haze periods in the NCP, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9793, https://doi.org/10.5194/egusphere-egu2020-9793, 2020

D3584 |
EGU2020-3202
Jun Zheng, Xiaowen Shi, and Yan Ma

A suite of instruments were deployed to simultaneously measure nitrous acid (HONO), nitrogen oxides (NOx= NO + NO2), carbon monoxide (CO), ozone (O3), volatile organic compounds (VOCs, including formaldehyde (HCHO)) and meteorological parameters near a typical industrial zone in Nanjing of the Yangtze River Delta region, China. High levels of HONO were detected using a wet chemistry-based method. HONO ranged from 0.03-7.04 ppbv with an average of 1.32 ±0.92 ppbv. Elevated daytime HONO was frequently observed with a minimum of several hundreds of pptv on average, which cannot be explained by the homogeneous OH + NO reaction (POH+NO) alone, especially during periods with high loadings of particulate matters (PM2.5). The HONO chemistry and its impact on atmospheric oxidation capacity in the study area were further investigated using a MCM-box model. The results show that the average hydroxyl radical (OH) production rate was dominated by the photolysis of HONO (7.13×106molecules cm-3 s-1), followed by ozonolysis of alkenes (3.94×106molecules cm-3 s-1), photolysis of O3(2.46×106molecules cm-3 s-1) and photolysis of HCHO (1.60×106molecules cm-3 s-1), especially within the plumes originated from the industrial zone. The observed similarity between HONO/NO2and HONO in diurnal profiles strongly suggests that HONO in the study area was likely originated from NO2heterogeneous reactions. The averagenighttimeNO2to HONO conversion ratewas determined to be ~0.9% hr-1. Good correlation between nocturnal HONO/NO2and the products of particle surface area density (S/V) and relative humidity (RH), S/V×RH,supports the heterogeneous NO2/H2O reaction mechanism. The other HONO source, designated as Punknonwn, was about twice as much as POH+NO on average and displayed a diurnal profile with an evidently photo-enhanced feature, i.e., photosensitized reactions of NO2may be an important daytime HONO source. Nevertheless, our results suggest that daytime HONO formation was mostly due to the light-induced conversion of NO2on aerosol surfaces but heterogeneous NO2reactions on ground surface dominated nocturnal HONO production. Concurred elevated HONO and PM2.5levels strongly indicate that high HONO may increase the atmospheric oxidation capacity and further promote the formation of secondary aerosols, which may in turn synergistically boost NO2/HONO conversion by providing more heterogeneous reaction sites.

How to cite: Zheng, J., Shi, X., and Ma, Y.: Heterogeneous formation of HONO and its impacts on haze formation in the YRD region of China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3202, https://doi.org/10.5194/egusphere-egu2020-3202, 2020

D3585 |
EGU2020-13236
Yong Lim, Duong Do, Hyun Jin, Jiwon Lee, and Jin Young Kim

High–concentration particulate matter (PM) at East Asia threatens human health and potentially alters climate. High levels of SO2, NOx and NH3 emissions attribute the formation of inorganics including sulfates, nitrates and ammoniums in PM. Consequently, PM contains a large fraction of these inorganics, and aerosol liquid water (ALW) is considered to promote inorganic PM formation. A thermodynamic model has been used to estimate inorganic concentrations and a pH of PM because PM can be viewed as an ammonium-sulfate-nitrate-water system, which maintains thermodynamic equilibriums between the gas and particle phase and in the aqueous phase within particles. However, gas–particle partitioning of semivolatile inorganic species (i.e., NH3–NH4 + and HNO3–NO3-) particularly influenced by organics and aqueous-phase secondary organic aerosol (aqSOA) formation in PM through multiphase chemistry are not well understood.

We conducted smog chamber experiments for OH-radical initiated reactions of toluene in the presence of ammonium sulfate seed particles under high NOx, NH3 and humid conditions, which were similar to high-concentration haze conditions at Seoul, Korea. Measurements of inorganic concentrations in particles agree well with outputs of thermodynamic model simulations. The nitrate increase in seed particles is most prominent because ALW enhances the uptake of total HNO3 photochemically formed from NOx. We identified methylglyoxal as a precursor for aqSOA formation. It appears that organics attribute ALW formation under deliquescence relative humidity for inorganic salts. We further investigated the response of particle mass concentrations to various NOx concentrations, which can be useful for NOx controls for PM reduction.

How to cite: Lim, Y., Do, D., Jin, H., Lee, J., and Kim, J. Y.: Photochemistry of toluene under high NOx, NH3 and humid conditions in the presence of inorganic seed particles: a smog chamber study for urban haze formation at East Asia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13236, https://doi.org/10.5194/egusphere-egu2020-13236, 2020

D3586 |
EGU2020-12014
Guo Li, Hang Su, Nan Ma, Guangjie Zheng, Uwe Kuhn, Meng Li, Thomas Klimach, Ulrich Pöschl, and Yafang Cheng

Direct measurement of the acidity (pH) of ambient aerosol particles/droplets has long been a challenge for atmospheric scientists.  A novel and facile method was introduced recently by Craig et al. (2018), where the pH of size-resolved aerosol droplets was directly measured by two types of pH-indicator papers (pH ranges: 0 – 2.5 and 2.5 – 4.5) combined with RGB-based colorimetric analyses using a model of G-B (G minus B) versus pH2.  Given the wide pH range of ambient aerosols, we optimize the RGB-based colorimetric analysis on pH papers with a wider detection range (pH ~ 0 to 6).  Here, we propose a new model to establish the linear relationship between RGB values and pH: pHpredict = a×Rnormal + b×Gnormal + c×Bnormal.  This model shows a wider applicability and higher accuracy than those in previous studies, and is thus recommended in future RGB-based colorimetric analyses on pH papers.  Moreover, we identify one type of pH paper (Hydrion® Brilliant pH dip stiks, Lot Nr. 3110, Sigma-Aldrich) that is more applicable for ambient aerosols in terms of its wide pH detection range (0 to 6) and strong anti-interference capacity.  The determined minimum sample mass (~ 180 µg) highlights its potential to predict aerosol pH with a high time resolution (e.g., ≤ 1 hour).  We further show that the routinely adopted way of using pH color charts to predict aerosol pH may be biased by the mismatch between the standard colors on the color charts and the real colors of investigated samples.  Thus, instead of using the producer-provided color chart, we suggest an in-situ calibration of pH papers with standard pH buffers.

Reference:

Craig, et al., Direct determination of aerosol pH: Size-resolved measurements of submicrometer and supermicrometer aqueous particles. Analytical Chemistry, 90 (19), 11232-11239, 2018.

Cheng, et al., Reactive nitrogen chemistry in aerosol water as a source of sulfate during haze events in China. Science Advances, 2 (12), e1601530, 10.1126/sciadv.1601530, 2016.

Zheng, et al., Exploring the severe winter haze in Beijing: The impact of synoptic weather, regional transport and heterogeneous reactions. Atmospheric Chemistry and Physics, 15, 2969-2983, 2015.

Li, et al., Multifactor colorimetric analysis on pH-indicator papers: an optimized approach for direct determination of ambient aerosol pH, Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2019-394, in review, 2019.

How to cite: Li, G., Su, H., Ma, N., Zheng, G., Kuhn, U., Li, M., Klimach, T., Pöschl, U., and Cheng, Y.: Multifactor colorimetric analysis on pH-indicator papers: an optimized approach for direct determination of ambient aerosol pH, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12014, https://doi.org/10.5194/egusphere-egu2020-12014, 2020

D3587 |
EGU2020-2340
Zhe Chen, Na Wang, Shu-Feng Pang, and Yun-Hong Zhang

Due to significant influence on global climate and human health, atmospheric aerosols have attracted numerous interests from the atmospheric science community. To provide insight into the aerosol effect, it is indispensable to investigate the aerosol properties comprehensively.

Since atmospheric aerosols are surrounded by substantial gas phase and have high specific surface area, the composition partitioning between particle phase and gas phase must be considered as a key aerosol property, which is termed as volatility for volatile organic/inorganic components. Recent studies show that the aerosol volatility can also be induced by the reaction of components in addition to the volatile compositions. Herein, we summarize four types of volatility induced by reaction, namely chloride depletion, nitrate depletion, ammonia depletion and volatility induced by salt hydrolysis. For chloride depletion and nitrate depletion, these processes can be regarded as reactions that strong acids are substituted by weak acids. The high volatility of the formed HCl or HNO3 drives the reaction continuously moving forward.

For ammonium depletion, we observed the reaction occurs between (NH4)2SO4 and organic acid salts during dehydration process by ATR-FTIR. For example, when molar ratio is 1:1, significant depletion of ammonium was observed in the disodium succinate/(NH4)2SO4 particles, indicating the evaporation of NH3. Besides, the hygroscopicity of the aerosol particles decreased after the dehydration, which should be attributed to the formation of less hygroscopic succinic acid and ammonium depletion. By regarding organic acid salts as weak bases, the ammonium depletion is a reaction that strong base substituted by weak base, driving by the continuous release of NH3. In addition to volatility induced by reactions within multi-component aerosols, we also found that the salt hydrolysis can also cause the formation of volatile product. For magnesium acetate (MgAc2) aerosols, we found significant water loss of the aerosol particles under constant relative humidity condition, while the amount of acetate was also decreased. We infer that the acetic acid (HAc) evaporation is caused by the hydrolysis of MgAc2, leading to the volatility and declined hygroscopicity. Two factors contribute to the volatility of MgAc2 aerosols. One is the volatile acid donner (Ac2-), which can lead to the formation of volatile HAc. The other is the residual ion accepter (Mg2+), which can combine residual OH- after the proton is depleted by the evaporation of HAc. The formation of insoluble Mg(OH)2 effectively maintains the aqueous pH in a suitable range, keeping the reaction moving forward. It should be noted that the co-exist of volatile acid donner and residual ion accepter is indispensable for the volatility induced by hydrolysis.

Generally, for the volatile species present in atmosphere, the aerosol volatility induced by the reaction of components can be an important pathway for their recycling processes. Due to the substantial composition modification, the hygroscopicity is also affected by such reaction. Therefore, this partitioning behavior of aerosols needs to be considered in the future atmospheric aerosol study, which may prevent the underestimate of particle volatilization or overestimate of hygroscopicity.

How to cite: Chen, Z., Wang, N., Pang, S.-F., and Zhang, Y.-H.: How Are Strong Acids or Strong Bases Substituted by Weak Acids or Weak Bases in Aerosols?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2340, https://doi.org/10.5194/egusphere-egu2020-2340, 2020

D3588 |
EGU2020-8194
Ning Yang, Yanru Bai, Yong Zhu, Nan Ma, and Qiaoqiao Wang

In the last six years, China has experienced significant improvement in air quality due to great emission reduction efforts. However, ozone concentrations are still slowly increasing in three major regions of eastern China, respectively Jing-Jin-Ji(JJJ), Yangtze River Delta region(YRD) and Pearl River Delta region(PRD). It is shown from the 2015-2018 national urban air quality real-time release platform that the surface ozone in JJJ, YRD and PRD has increased each year and reached the highest in 2018. The monthly ozone concentration peaked in June in almost all cities of JJJ, while it had multiple peaks in other two regions (summer and autumn in YRD - and February, May and September in PRD). Simulation with a chemical transport model(GEOS-Chem) indicates that the formation of ozone is affected by the optical properties of PM2.5 and also the heterogeneous uptake of N2O5 on sea salt aerosol.

How to cite: Yang, N., Bai, Y., Zhu, Y., Ma, N., and Wang, Q.: Exploring the trends and potential drivers of surface ozone in eastern China in 2015-2018, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8194, https://doi.org/10.5194/egusphere-egu2020-8194, 2020

D3589 |
EGU2020-19363
Lixia Liu, Hang Su, Ulrich Pöschl, and Yafang Cheng

Particle production in the upper troposphere has been reported as an important source of aerosol particles and cloud condensation nuclei in pristine environment and tropical regions and exerts significant climate effects. In this work, we develop a new organic nucleation scheme to the WRF-Chem model with extended particle size bins from 1nm to 10μm. We improve on previous coarse-resolution global simulations that approximate the highly oxygenated multifunctional organic compounds (HOMs) in a thermodynamic state by implementing kinetic calculation of HOMs and using fine-grid regional simulations. Sensitivity studies are conducted over the Amazon Basin during the dry season in 2014 to characterize the HOMs-induced new particle formation and identify its key controlling factors in Amazon. The model simulations are evaluated using aircraft observations of profiles of aerosol particles during the 2014 ACRIDICON-CHUVA campaign. We show that the new particle formation occurs mostly at the upper troposphere and modestly in the planetary boundary layer, driven by low temperature and high concentration of biogenic precursors, respectively. Including the HOMs-induced biogenic new particle formation mechanism decreases the model prediction bias of the particle number concentration in the upper troposphere by over 50%, suggesting an important role of the HOMs-induced biogenic new particle formation in the dry season over the Amazon region.

How to cite: Liu, L., Su, H., Pöschl, U., and Cheng, Y.: Particle production in the upper troposphere over the Amazon Basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19363, https://doi.org/10.5194/egusphere-egu2020-19363, 2020

D3590 |
EGU2020-16757
Hang Su, Nan Ma, Yele Sun, Jiangchuan Tao, Pingqing Fu, and Yafang Cheng

Fine-particle pollution associated with winter haze threatens the health of more than 400 million people in the North China Plain. The Multiphase chemistry experiment in Fogs and Aerosols in the North China Plain (McFAN) investigated the physical-chemical mechanisms leading to the haze formation with a focus on the contributions of multiphase processes in aerosol and fogs. We integrated multiple platform observations with regional and box models to identify the key oxidation process producing sulfate, nitrate and secondary organic aerosols, and their impact. A new environmental chamber was deployed to conduct kinetic experiments with real atmospheric compositions in comparison to literature kinetic data from laboratory studies. The experiments were carried out for multiple years since 2017 at the Gucheng site in the center of polluted areas and have performed experiments in the winter season. The location of the site minimizes fast transition between clean and polluted air masses (e.g., in Beijing), and helps to maintain a pollution regime representative for the North China Plain. The multi-year consecutive experiments documented the trend of PM2.5 pollution and corresponding change of aerosol physical and chemical properties, and allowed to investigate newly proposed mechanisms. The preliminary results show new proofs of the key role of aqueous phase reactions in regulating the aerosol compositions during haze events.

Reference:

Zheng et al., Exploring the severe winter haze in Beijing: the impact of synoptic weather, regional transport and heterogeneous reactions. Atmospheric Chemistry and Physics 15, 2969-2983 (2015).

Cheng et al., Reactive nitrogen chemistry in aerosol water as a source of sulfate during haze events in China. Science Advances 2,  (2016).

Li et al., Multifactor colorimetric analysis on pH-indicator papers: an optimized approach for direct determination of ambient aerosol pH. Atmos. Meas. Tech. Discuss. 2019, 1-19 (2019).

Kuang et al., Distinct diurnal variation of organic aerosol hygroscopicity and its relationship with oxygenated organic aerosol. Atmos. Chem. Phys. Discuss. 2019, 1-33 (2019).

 

How to cite: Su, H., Ma, N., Sun, Y., Tao, J., Fu, P., and Cheng, Y.: McFAN experiment: An integrated analysis of the multiphase chemistry experiment in Fogs and Aerosols in the North China Plain, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16757, https://doi.org/10.5194/egusphere-egu2020-16757, 2020

D3591 |
EGU2020-8156
Particle number size distribution measurements of PM1 and PM10 in fogs and implications on fog droplet evolutions
(withdrawn)
Jiangchuan Tao, Nan Ma, Yanyan Zhang, Ye Kuang, Juan Hong, Hang Su, and Yafang Cheng
D3592 |
EGU2020-1438
Jingwei Zhang and Junling An

Recent wintertime observations in north China found high concentrations of nitrous acid (HONO), secondary organic aerosols (SOA) and peroxyacetyl nitrate (PAN), especially during heavy haze periods, indicating stronger atmospheric oxidation capacity in winter haze days. Researchers speculated that HONO formation was enhanced in haze days through NO2 heterogeneous reaction on aerosol surfaces, and high concentrations of HONO during daytime further improved SOA and PAN formation.

In this study, the WRF-Chem model updated with six potential HONO sources was used to quantify the impacts of potential HONO sources on the production and loss rates of ROx ( OH+HO2+RO2) radicals, and on the concentrations of SOA and PAN in the Beijing-Tianjin-Hebei (BTH) region of China during wintertime of 2017. HONO simulations were greatly improved after considering the six potential sources, NO2 heterogeneous reactions were the main sources of HONO. HONO photolysis was the key precursors of primary OH while the contribution of O3 photolysis to OH could be neglected, the potential HONO sources remarkably accelerated ROx cycles, significantly improved SOA and PAN simulations, especially in heavy polluted periods. The above results suggest that the potential HONO sources should be considered in regional and global chemical transport models when conducting relevant studies.

How to cite: Zhang, J. and An, J.: Effect of potential HONO sources on ROx budgets and SOA and PAN formation in North China in winter, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1438, https://doi.org/10.5194/egusphere-egu2020-1438, 2019

D3593 |
EGU2020-1476
Yu Qu and Junling An

We coupled the heterogeneous hydrolysis of N2O5 into the newly updated Weather Research and Forecasting model with Chemistry (WRF-Chem) to reveal the relative importance of the hydrolysis of N2O5 and additional nitrous acid (HONO) sources for the formation of nitrate during high PM2.5 events in the North China Plain (NCP) in four seasons. The results showed that additional HONO sources produced the largest nitrate concentrations in winter and negligible nitrates in summer, leading to a 10% enhancement of a PM2.5 peak in southern Beijing and a 15% enhancement in southeastern Hebei in winter. In contrast, the hydrolysis of N2O5 produced high nitrate in summer and low nitrate in winter, with the largest contribution of nearly 20% for a PM2.5 peak in southeastern Hebei in summer. During PM2.5 explosive growth events, the additional HONO sources played a key role in nitrate increases in southern Beijing and southwestern Hebei in winter, whereas the hydrolysis of N2O5 contributed the most to a rapid increase in nitrate in other seasons. HONO photolysis produced more hydroxyl radicals, which were greater than 1.5 μg m-3 h-1 in the early explosive stage and led to a rapid nitrate increase at the southwestern Hebei sites in winter, while the heterogeneous reaction of N2O5 contributed greatly to a significant increase in nitrate in summer. The above results suggest that the additional HONO sources and the heterogeneous hydrolysis of N2O5 contributed the most to nitrate formation in NCP in winter and summer, respectively.

How to cite: Qu, Y. and An, J.: Seasonal effects of additional HONO sources and the heterogeneous reactions of N2O5 on nitrate in the North China Plain, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1476, https://doi.org/10.5194/egusphere-egu2020-1476, 2019

D3594 |
EGU2020-6458
Wenfei Zhu, Shengrong Lou, and Song Guo

As a characteristic pollutant of urban compound pollution, submicron particulate matter (PM1) has significantly impacted on human health and climate change. In this study, four intensive campaigns using a high-resolution time-of-flight AMS (HR-ToF-AMS) and other online instruments from 2016 to 2017 were conducted to investigate the seasonal characteristics of submicron particles in Shanghai. The average mass concentrations of submicron particulate matter during spring, summer, autumn and winter observations in Shanghai are 23.9 ± 20.7 μg/m3, 28.5 ± 17.6 μg/m3, 22.0 ± 17.2 μg/m3 and 31.9 ± 22.7 μg/m3, respectively. The major chemical components in submicron particulate matter showed obvious seasonal and daily variations. The increase of submicron particulate matter is mainly due to the contribution of nitrate in spring, autumn and winter, while the photochemical reaction promotes the rapid growth of sulfate in summer. Detailed source apportionment of organic aerosol showed that the fraction of more oxidized oxygenated organic aerosol in organic aerosol in spring was much lower than primary organic aerosol. Oxygenated organic aerosol dominated organic aerosol in summer (69%). More oxidized oxygenated organic aerosol account for 28% in autumn, suggesting that organic aerosol was aging. The liquid phase oxidation and the strong photochemical reaction concentration have a significant contribution to the formation of more oxidized oxygenated organic aerosol and less oxidized oxygenated organic aerosol in the spring, summer and winter observations, respectively. However, the photochemical reaction process dominated the formation of more oxidized oxygenated organic aerosol in autumn.

How to cite: Zhu, W., Lou, S., and Guo, S.: Seasonal variations in chemical characterization of submicron aerosol particles in Shanghai, China: Insights from a high-resolution aerosol mass spectrometry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6458, https://doi.org/10.5194/egusphere-egu2020-6458, 2020

D3595 |
EGU2020-21501
Jiaping Wang, Jinbo Wang, Wei Nie, Xuguang Chi, Jiandong Wang, and Aijun Ding

Haze pollution is a serious air quality concern in China up to now, which occurs frequently in mega city clusters, e.g. Beijing-Tianjin-Hebei and Yangtze River Delta region, especially in the cold season. Understanding the dominating secondary aerosol formation processes is vital for improving the prediction and emission control strategy of haze pollution. In this study, we reported measurements of aerosol chemical composition using the soot particle aerosol mass spectrometer (SP-AMS) at a regional background station, the Station for Observing Regional Processes of the Earth System (SORPES), in Nanjing, eastern China. Characteristics of aerosol chemical composition and dominating secondary aerosol formation processes were analyzed during typical haze events and compared with that in clean episodes. Sources and transportation of organic aerosol were performed using positive matrix factorization (PMF) together with backward Lagrangian particle dispersion modeling (LPDM).

How to cite: Wang, J., Wang, J., Nie, W., Chi, X., Wang, J., and Ding, A.: Aerosol chemical composition and formation of secondary aerosol during haze events at the SORPES station in China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21501, https://doi.org/10.5194/egusphere-egu2020-21501, 2020

D3596 |
EGU2020-19029
Maud Leriche and Aurélie Colomb and the BIO-MAÏDO

BIO-MAÏDO is a French collaborative program founded by the ANR (Agence Nationale de La Recherche). BIO-MAÏDO aims at better understanding the chemical and biological multiphasic mechanisms that control the Secondary Organic Aerosol (SOA) formation. The tropical environment of the Reunion Island represents an ideal site to study SOA formation: (1) numerous biogenic volatile organic compounds, precursors of SOA are emitted in huge amount and the high solar intensity flux and the temperature favors their chemical transformations; (2) due to the high occurrence of orographic clouds over this region, this site allows evaluating the influence of aqueous processes on SOA formation. The strategy adopted is based on an intensive field campaign over several sites with the objective to characterize sources of gases and aerosols and to evaluate multiphasic pathways controlling the formation and oxidation of SOA. This work is done in synergy with modeling investigations using a lagrangian particle dispersion model (FLEXPART), a 0D process cloud model (CLEPS) together with a 3D chemistry/transport model (Meso-NH).

The campaign took place from 13th of March to 4th of April 2019 at La Réunion Island. The main objectives were to document the cloud cycle on the slope of the Maïdo, the boundary layer development and the chemical evolution of atmospheric composition (primary and secondary aerosols as well as gaseous precursors) along the slope up to the receptor site, the Maïdo observatory. For this reason, the campaign took place on five sites distributed on the slope from the Maïdo to the observatory. A innovative instrumentation was deployed: three PTR-MS, a tethered balloon, an instrumented mast measuring biogenic volatile organic compounds fluxes, a mobile mast with a cloud impactor, etc. Preliminary results from the campaign will be presented.

How to cite: Leriche, M. and Colomb, A. and the BIO-MAÏDO: The BIO-MAÏDO (Bio-physicochemistry of tropical clouds at Maïdo (La Réunion Island): processes and impacts on secondary organic aerosols formation) campaign, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19029, https://doi.org/10.5194/egusphere-egu2020-19029, 2020

D3597 |
EGU2020-12532
Qiaorong Xie and Pingqing Fu

Firework (FW) emissions have strong impacts on air quality and public health. However, little is known about the molecular composition of FW-related aerosols especially the organic fraction. Here we describe the detailed molecular composition of Beijing aerosols collected before, during, and after a FW event in New Year's Eve evening. Subgroups of CHO, CHNO, CHOS, and CHNOS were characterized using ultrahigh resolution Fourier transform-ion cyclotron resonance (FT-ICR) mass spectrometry. We found that high molecular weight compounds with relatively low H/C and O/C ratios and high degree of unsaturation were greatly enhanced during the New Year’s Eve, which are likely to be aromatic-like compounds. They plausibly contributed to the formation of brown carbon and affect the light absorption properties of atmospheric aerosols. Moreover, the number concentration of sulfur-containing compounds especially the nitrooxy-organosulfate was increased dramatically by the FW event, suggesting the important effect of nighttime chemistry on their formation. But, the number concentration of CHO and CHON doubled after the event with photooxidation. The co-variation of these subgroups was suggested to be associated with multiple atmospheric aging processes of aerosols including the multiphase redox chemistry driven by NOx, O3, and ·OH. Our study provides new insights into the anthropogenic emissions for urban SOA formation.

How to cite: Xie, Q. and Fu, P.: Molecular Characterization of Firework-Related Urban Aerosols using FT-ICR Mass Spectrometry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12532, https://doi.org/10.5194/egusphere-egu2020-12532, 2020

D3598 |
EGU2020-8008
Qian Wu, Xiao Tang, Lei Kong, Miaomiao Lu, and Zifa Wang

Sulfate, nitrate, ammonium, organic carbon and black carbon are the key components of PM2.5, but their simulations are still facing high uncertainty. Exploring the sources of such uncertainty is important for the modeling of PM2.5 and the understanding of atmospheric chemical processes. This study aims to evaluate and investigate the modeling uncertainty of these aerosols over Pearl River Delta (PRD) region based on Monte Carlo simulations of a Nested Air Quality Prediction Modeling System (NAQPMS) during 2015. Emission inventory as one of the most important uncertainty sources are perturbed according to their uncertainties to derive 50 ensemble simulations of NAQPMS with 15km horizontal resolution. The surface observations of sulfate, nitrate, ammonium, OC and BC from 10 sites in PRD region for one year are used to evaluation the performance of the ensemble mean estimation of the simulations. The results suggested that the ensemble mean could well reproduce the spatial and temporal variations of nitrate, ammonium, OC and BC with the correlation coefficients above 0.74 and their mean bias less than 2μg·m-3 . However, the model has poor skills in the sulfate modeling with the correlation coefficients 0.26 and remarkable underestimation in winter. Further analysis for such modeling uncertainties suggested that the uncertainties in emissions can explain most of modeling uncertainties for BC and OC. However, the biases in sulfate and ammonium modeling especially during the wintertime are probably caused by the uncertainty in heterogeneous reaction modeling. The above results provide an overall assessment of the uncertainty in inorganic aerosol modeling over PRD region and can serve a basis for its simulation improvement.

How to cite: Wu, Q., Tang, X., Kong, L., Lu, M., and Wang, Z.: Evaluation of multi-component ensemble simulation of PM2.5 in the Pearl River Delta region, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8008, https://doi.org/10.5194/egusphere-egu2020-8008, 2020

D3599 |
EGU2020-12155
Yaqing Zhou, Nan Ma, Zhibin Wang, Linhong Xie, Baofang Xie, Shaowen Zhu, Xihao Pan, Sen Wu, Hang Su, and Yanfang Cheng

Effective density is one of the most important physical property of atmospheric aerosols, which is link to particle formation and aging process. Combined characterization of density, chemical composition and source evolution of aerosol is crucial for understanding their interactions and effects on environment and climate. The effective density of sub-micrometer aerosol particles was investigate at a heavily polluted rural site in the North China Plain from 16 October to 1 November 2019. 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 selected diameters of 50, 100, 150, 220 and 300 nm. The measured effective density is higher during clean period than pollution period, with average values ranged from 1.13 to 1.36 g/cm3, which is lower than the reported values in Shanghai and Beijing. Similar diurnal cycles of effective density are observed for the five diameters, that is, started to increase in the morning and reached a peak in the afternoon around 13:00-16:00, then decreased and remained at a relative low value during the night. Two valleys are found during morning and evening rush hours for particle diameter smaller than 150 nm, which is likely to stem from the higher fresh emissions such as BC, BBOA and HOA. In most cases, measured particle effective density shows a single-modal distribution. But during clean days, bimodal distribution was observed with an extra low-density mode peaking at around 0.5 -1.0 g/cm3, which may be attributed to freshly emitted soot particles.

How to cite: Zhou, Y., Ma, N., Wang, Z., Xie, L., Xie, B., Zhu, S., Pan, X., Wu, S., Su, H., and Cheng, Y.: Size-resolved effective density of submicron particles during autumn in the North China Plain, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12155, https://doi.org/10.5194/egusphere-egu2020-12155, 2020

D3600 |
EGU2020-20887
Chandra Mouli Pavuluri, Subba Rao Devineni, Zhanjie Xu, Kimitaka Kawamura, Pingqing Fu, Yan-Lin Zhang, and Cong-Qiang Liu

Secondary organic aerosols (SOA) that account for a substantial and often a dominant fraction of total OA mass are formed by photooxidation of various precursors derived from anthropogenic and biogenic sources in the atmosphere. They have serious impacts on the Earth’s climate system directly by scattering and absorbing solar radiation and indirectly by acting as cloud condensation nuclei, and adverse effects on human health. In recent times, considerable attention has been paid on laboratory studies, preferably in gas-phase, in order to understand the chemistry of SOA formation. However, the studies on SOA formation in aqueous phase are limited, which are mainly focused on high abundant volatile organic compounds (e.g., isoprene) and/or their oxidation products, but not on fatty acids (except oleic acid). To better understand the air-water interface photochemistry of fatty acids and their transformations to lower homologous monoacids and more oxygenated species such as diacids and related compounds in atmospheric waters (fog, cloud and aqueous aerosol), we conducted batch UV irradiation experiments on a saturated (stearic acid, C18H36O2) and an unsaturated (linoleic acid, C18H32O2) fatty acids for different time periods (age, 0-120 h) in aqueous-phase. All the irradiated samples were analyzed for measurements of mono- and di-acids, oxoacids and α-dicarbonyls. We found high abundances of monoacids followed by diacids, pyruvic acid and α-dicarbonyls in less aged samples, whereas C3 and C4 diacids were abundant in the more aged samples. Our results imply that the photochemical oxidation of fatty acids and subsequent transformations of the product species in atmospheric waters are significant and their contribution to more oxygenated SOA is increased with aging in the atmosphere.

How to cite: Pavuluri, C. M., Devineni, S. R., Xu, Z., Kawamura, K., Fu, P., Zhang, Y.-L., and Liu, C.-Q.: Formation of low molecular weight mono- and di-carboxylic acids and related compounds from photochemical oxidation of stearic and linoleic acids in aqueous-phase, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20887, https://doi.org/10.5194/egusphere-egu2020-20887, 2020

D3601 |
EGU2020-12389
Peng Cheng, Manman Zhang, and Yongjie Li

The dithiothreitol (DTT) assay is widely used to characterize the Oxidation Potential (OP) of atmospheric particulate matter (PM), which can cause adverse effects on human health. However, it’s under debate which chemical species determines the consumption rate of DTT. During January and April 2018, we measured the improved DTT assay of daily PM2.5 samples collected in Guangzhou, China with complimentary measurements of water-soluble ions, organic/elemental carbon (OC/EC) and metal elements. The average sampled air volume normalized consumption rate of DTT (DTTv) was 4.67 ±1.06 and 4.45 ± 1.02 nmol min-1 m-3, in January and April, respectively while the average PM2.5 mass normalized consumption rate of DTT (DTTm) was 13.47 ± 3.86 and 14.66 ± 4.49 pmol min-1 μg-1. Good correlations were found between DTTv and concentration of PM2.5, OC, and EC while no correlation was found between DTTm and concentrations of water-soluble ions, OC, EC or metal element, which is consistent with most early observations. We also evaluated the contribution of soluble metals to DTT assay by addition of EDTA, a strong metal chelator. We found that nearly 90% of DTTv and DTTm were reduced by EDTA, suggesting a dominant role of soluble metals in determining the response of DTT to ambient PM2.5. Based on responses of DTT to soluble metals in literature, we found that Cu(II) and Mn(II) are the major contributors to OP of PM2.5 in Guangzhou. The correlation coefficient between DTTm and OC shows a clear increase after addition of EDTA, implying that the response of DTT to quinones is not strongly suppressed by EDTA.

How to cite: Cheng, P., Zhang, M., and Li, Y.: Oxidative Potential and Chemical Characteristics of Ambient PM2.5 in Guangzhou, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12389, https://doi.org/10.5194/egusphere-egu2020-12389, 2020

D3602 |
EGU2020-14982
Wei Tao, Hang Su, Guangjie Zheng, Jiandong Wang, Lixia Liu, Chao Wei, Meng Li, Qiang Zhang, Ulrich Poschl, and Yafang Cheng

Understanding the formation mechanism of severe haze is crucial for the development of efficient pollution control strategy. Recently, multiphase reactions in aerosol water has been suggested as an important source of sulfate aerosol during severe haze (Zheng et al., 2015;Cheng et al., 2016). Though several oxidation mechanisms have been recognized, the dominant oxidation pathway is still under debate reflecting a missing consensus. Based on a model survey with Weather Research and Forecasting model coupled with Chemistry (WRF-Chem), we have investigated the variability of aerosol pH and regimes of sulfate formation through multiphase oxidation during the haze episodes in January of 2013. Our results show a large spatial and temporal variability in the aerosol pH and sulfate formation regimes. Surface aerosol pH shows a clear diurnal variation with low pH during daytime and high pH during night-time for most cases. Aerosol pH tends to decrease with increasing altitude in the lower atmosphere. For the scenario best reproduces the observations in Beijing, NO2, TMI+O2, O3 and H2O2 pathways can all dominate the production of sulfate in specific areas of the Beijing-Tianjin-Hebei (BTH) region. With the increasing height, O3 pathway and gas phase oxidation by OH radicals become more important. Moreover, sensitivity tests also suggest that, emissions of crustal particles, NH3 and soluble iron/manganese have great impacts on aqueous phase chemistry, and should be better constrained in future studies.

References:

Zheng, G. J., Duan, F. K., Su, H., Ma, Y. L., Cheng, Y., Zheng, B., Zhang, Q., Huang, T., Kimoto, T., Chang, D., Poschl, U., Cheng, Y. F., and He, K. B.: Exploring the severe winter haze in Beijing: the impact of synoptic weather, regional transport and heterogeneous reactions, Atmos. Chem. Phys., 15, 2969-2983, 10.5194/acp-15-2969-2015, 2015.

Cheng, Y. F., Zheng, G. J., Wei, C., Mu, Q., Zheng, B., Wang, Z. B., Gao, M., Zhang, Q., He, K. B., Carmichael, G., Poschl, U., and Su, H.: Reactive nitrogen chemistry in aerosol water as a source of sulfate during haze events in China, Sci Adv, 2, e1601530, UNSP e1601530,10.1126/sciadv.1601530, 2016.

How to cite: Tao, W., Su, H., Zheng, G., Wang, J., Liu, L., Wei, C., Li, M., Zhang, Q., Poschl, U., and Cheng, Y.: Aerosol pH and regime transition of sulfate formation in aerosol water during winter haze events in northern China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14982, https://doi.org/10.5194/egusphere-egu2020-14982, 2020

D3603 |
EGU2020-21217
zhijie zhang

             After years of development, Mie lidar has become an important technical means to explore aerosol particles in the atmosphere, and has been widely used to explore the optical and physical properties of aerosols in atmosphere. By Using backscatter signal collecting by lidar, optical characteristics of aerosols can be qualitatively analyzed. However, in order to get the actual value of optical parameters, the accurate lidar ratio (LR) (the ratio of extinction coefficient to back-scattering coefficient) is needed in inversion.

            Using the Mie scattering theory, the key parameter of inversion: LR, can be measured out. The value of LR has been discussed in detail by changing complex refractive index, size parameter  and field angle of a single particle. It is found that when the scale parameter is greater than 0.6, the value of LR increases first and then decreases with the increasing scale parameter, and there are several extremums; the value of LR decreases with the increasing imaginary part of the complex refractive index; the value of LR increases with the increasing filed angle.

            To study the influence of different mixing states on optical parameters of aerosol clusters, a three-component optical equilibrium spherical aerosol model is assumed. The results shows that when the mixing states of aerosol are complete external mixture, complete uniform internal mixture and complete coated mixture, the value of LR appears to be: complete uniform internal mixture > complete external mixture > complete coated mixture.

            Assuming that the hygroscopic growth factor of aerosol is a constant which does not increase with the particle size and its value is GF = 1.5[p2] , the value of LR after hygroscopic growing is discussed. It is found that the value of LR will increase after hygroscopic growing, but it still follows the law that: complete uniform internal mixture > complete external mixture > complete coated mixture.

            By correcting the value of LR, accurate extinction coefficient and back-scattering coefficient can be measured out with inversion. The production of lidar will be quantified instead of qualitative after doing this.

How to cite: zhang, Z.: Study on the influence of different aerosol mixing states on lidar ratio, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21217, https://doi.org/10.5194/egusphere-egu2020-21217, 2020

D3604 |
EGU2020-18014
Shaowen Zhu, Nan Ma, Xihao Pan, Wenlin Dong, Jiangchuan Tao, Juan Hong, Yuxuan Zhang, Guo Li, Jeannine Ditas, Hang Su, and Yafang Cheng

Black carbon (BC) is the most important light absorbing component in the atmosphere and has significant impacts on the climate, environment and public health. Its effects depend not only on its spatial-temporal distribution, but also on its physico-chemical characteristics. Mixing state is one of the most important properties of BC and strongly determines its hygroscopicity and radiative properties. During an intensive field campaign conducted in the North China Plain in winter 2018, mass-based mixing state of BC-containing particles were online measured with a Centrifugal Particle Mass Analyzer and Single Particle Soot Photometer (CPMA-SP2) tandem system. This technique directly provides the mass ratio of non-refractory coating matter to BC core (MR) in individual particles and does not require to assume the density, morphology and refractive index of BC core and coating in data retrieval, therefore has lower uncertainly compared with leading-edge fit technique. In our measurement, the mean number fraction of uncoated (MR=0), thin coated (0<MR<3) and thick coated (MR≥3) BC-containing particle during the campaign were respectively ~10%, ~35% and ~55%, indicating the strong aging process of BC-containing particle in the North China Plain. The median value of MR was much higher in polluted days than clean days, for example, the median value of MR with a particle mass of 8.56 fg (~220 nm in diameter) for polluted and clean days were ~3.2 and ~1.6, respectively. The mixing state of BC-containing particles obtained by different methods were also compared and evaluated.

How to cite: Zhu, S., Ma, N., Pan, X., Dong, W., Tao, J., Hong, J., Zhang, Y., Li, G., Ditas, J., Su, H., and Cheng, Y.: Mass-based mixing state of black carbon measured by a tandem CPMA-SP2 system in wintertime in the North China Plain, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18014, https://doi.org/10.5194/egusphere-egu2020-18014, 2020