Over the past decades, air pollution mitigation measures have been applied extensively in Europe with a direct impact on the particulate matter (PM) load and composition. The Mediterranean atmospheric aerosol burden is not only characterized by emissions from anthropogenic sources but is also strongly influenced by the arid areas of North Africa and the Middle East, the marine environment, and atmospheric transformation. Here, we analyse data from various databases to investigate the evolution of unregulated particulate pollutants, namely ultrafine particles (UFP), desert dust (DD) and black carbon (BC) in the Eastern Mediterranean region over the last 20 years. Ground-based (AERONET) and satellite-based (MODIS/Terra) remote sensing observations, reanalysis products (MERRA-2) and in-situ observations (Finokalia environmental research station - finokalia.chemistry.uoc.gr) were used to investigate the variability and the trends of atmospheric aerosols.

A decrease in the AOT was observed during the studied period, which was also reflected in the ground-based PM₁₀ measurements. In addition to the decrease in sulfate content observed as a result of EU regulations, the AOT of dust was found to be decreasing as well. At the same time a statistically significant increase in the Ångström exponent was observed for all datasets, suggesting that the overall size of aerosols in the eastern Mediterranean is decreasing.  Ground-based measurements of submicron atmospheric aerosol number concentrations showed an increase in total aerosol number, which was more pronounced for the UFP. At the same time, an increase in the absorption coefficient of aerosol particles was observed, indicating an increase in the BC content, which could contribute to the increase in UFP concentrations. Overall, it was found that despite the apparent decrease in aerosol constituents in terms of particulate matter due to the regulations applied in Europe over the last decades, pollutants such as BC and UFP, which are hazardous to human health and may influence climate at the regional scale, appear to be increasing and new approaches are required for effective clean air strategies.

How to cite: Kalivitis, N., Kanakidou, M., Gialesakis, N., Chatziparaschos, M., and Mihalopoulos, N.: Emerging atmospheric pollutants in southern Europe- trends and changes over the past two decades, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19864, https://doi.org/10.5194/egusphere-egu24-19864, 2024.

Long-term observations of atmospheric mercury are important for the evaluation of the effectiveness of the Minamata Convention on Mercury. We continuously measured gaseous elemental mercury (GEM) concentrations at four remote sites in China for more than ten years, i.e., Mt. Waliguan (100.90° E, 36.29° N) during 2008-2022, Mt. Changbai (128.11° E, 42.40° N) during 2008-2022, Mt. Ailao (101.02° E, 2453° N) during 2011-2022, and Mt. Damei (121.57° E, 29.63° N) during 2011-2022. Our observations showed that GEM concentrations in China increased slightly during 2008-2013, and then the GEM concentrations decreased significantly after 2013. The mean GEM concentrations at the four Chinese sites during 2022 were 1.51 ± 0.35 ng m^-3, which is close to mean concentrations observed in Europe, North America, the Arctic, and the free troposphere in Pacific Ocean during 2021 (Individual means: 1.14 to 1.51 ng m^-3, overall mean: 1.34 ± 0.11 ng m^-3, n = 13). During 2013-2022, GEM concentrations in China decreased by 35%, which was much higher than the decreasing rates observed in Europe (9%), North America (10%), the Arctic (6%), and the free troposphere in Pacific Ocean (9%) during 2013-2021. The declines in in GEM concentrations in China since 2013 matches well with the decreasing anthropogenic Hg emission in China estimated by Chinese anthropogenic Hg emission inventory, indicating the reduction in anthropogenic Hg emissions in China was the major driver for the GEM declines.

How to cite: Feng, X., Fu, X., and Zhang, H.: Combating air pollution significantly reduced air mercury concentrations in China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14646, https://doi.org/10.5194/egusphere-egu24-14646, 2024.

Regional transport plays a crucial role in the pollution of fine particulate matter (PM_2.5) over the Yangtze River Delta region (YRD). A practical joint regional emission control strategy requires quantitative assessment of the contribution of regional transport. In this study, the contribution of inter-city transport to PM_2.5 among the 41 cities in the YRD region were quantitatively estimated using a source-oriented chemical transport model, and then the relationship between the cumulative contribution of regional transport and the distance was examined using the Michaelis-Menten equation. The results show that the Michaelis-Menten equation is suitable to represent the relationship between the cumulative contribution and transport distance. The coefficient of determination (r²) of the fittings is greater than 0.9 in 71% of the cases in the six subregions and four seasons in YRD. Two key parameters in the Michaelis-Menten equation K₁, indicating the maximum contribution of regional transport, and K₂, indicating the distance to which the regional transport contribution reach half the maximum contribution, show substantial regional and seasonal variations. The average K₁ is 73.6%, with lower values observed in the northern part of the YRD and higher values in central Jiangsu. K₂ is larger in northern Jiangsu, as well as central and southern Zhejiang. The local contribution in autumn and winter is lower than that in spring and summer in the northern part of the YRD. Particularly in northern Jiangsu, the local contribution reaches 90.4% in summer but drops to 53.0% in autumn and winter, illustrating significant impacts of regional transport to PM_2.5 in autumn and winter in this area. K₂ is larger on polluted days, compared to clean days, indicating greater contributions from regional transport to PM_2.5 in YRD. The results can serve as a scientific foundation for implementing regional joint prevention and control measures in the YRD region.

How to cite: Hu, J., Gong, K., and Xie, X.: Seasonal quantification of the inter-city transport of PM2.5 in the Yangtze River Delta region of China based on a source-oriented chemical transport model and the Michaelis-Menten equation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10550, https://doi.org/10.5194/egusphere-egu24-10550, 2024.

Restrictions on economic activities during the COVID-19 pandemic lockdown period provided a once-in-a-lifetime opportunity for many countries including India to witness the improvement in air quality that can be achieved with a reduction in anthropogenic activities. Many previous studies have reported about the sudden drop in pollution levels across India as an immediate reflex of these economic restrictions or “lockdown”. However, there exist several shortcomings in most of these studies. Firstly, most studies focused only on the lockdown phases and ignored to document the recovery of pollution levels during the unlock phases. Secondly, many studies considered the reduction in emission sources only within India due to lockdown and ignored the reduction in activities in the neighboring counties. Thirdly, many studies could not separate the impact of emission reductions and changing meteorology throughout lockdown phases on the improvement in observed air quality. In the present study, we examine the impacts of changing emissions of air pollutants and meteorology during the entire lockdown and unlock phases of COVID-19 period (February 24 – June 30, 2020) on the air quality over India using the COvid-19 adjustmeNt Factors fOR eMissions (CONFORM) data and Weather Research and Forecasting model coupled to Chemistry (WRF-Chem) model.

We performed systematically designed model simulations to understand and isolate the effects of changing emissions of air pollutants and meteorology on the air quality levels during the COVID-19 period. In one case, we consider business as usual and another one we adjusted anthropogenic emissions using CONFORM data. To quantify and isolate the impact of changing meteorology during the same period, we performed additional simulations for the last five years that is from 2015 to 2019. All simulations are performed for a nested model domain having an inner domain horizontal resolution of 9Km x 9Km and centre around Bilaspur, Chhattisgarh, using 6-hourly ERA-5 reanalysis data. Model simulations are evaluated using available in-situ measurements and remote sensing data from various satellite observations.

Results from our emission-restricted simulations show that immediately before and after the imposition of the lockdown, particulate matter concentration decreased by ~36%, compared to a 20% decrease during the same periods in the last five years. Movement and Industrial restrictions and reductions in Power Production led to a significant decrease in surface distribution of NO_x (NO+NO₂) over different Indian metro cities (Kolkata ~52%, Delhi ~67%). Highly populated and polluted Northern and Western Indian states show distinct spatial variations, with the more critical decrease in CO (~21%), PM_2.5 (~27%), and SO₂ (~17%) pollutant levels. A significant reduction of NO_x to VOCs in VOC-limited urban locations shows a marginal increase in the O₃ distribution over Central and South India. We observed that, although there was an initial improvement in air quality due to strict activity restrictions during the first phase of the lockdown, most Indian megacities still failed to achieve the national standard of air pollutants. More results with greater details will be presented.

How to cite: Nandi, I., Ganguly, D., and Dey, S.: Assessing the impacts of emission reduction and meteorology change on India’s air quality during COVID-19 lockdown using the WRF-Chem model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19479, https://doi.org/10.5194/egusphere-egu24-19479, 2024.

In addition to causing atmospheric pollution, anthropogenic emissions also have impacts on ecosystems through atmospheric deposition, e.g., acidification and eutrophication owing to acid deposition (i.e., sulfur and nitrogen deposition). China currently has the globally highest acid deposition, yet research on its status, impacts, causes, and controls is lacking. Here, we compiled data and calculated critical loads regarding acid deposition. The results showed that the abatement measures in China have achieved a sharp decline in the emissions of acidifying pollutants and a continuous recovery of precipitation pH, despite the drastic growth of the economy and energy consumption. However, the risk of ecological acidification and eutrophication showed no significant decrease. With similar emission reductions, the decline in areas at risk of acidification in China (7.0%) lags behind Europe (20%) or the USA (15%). This was because, unlike Europe and the USA, China's abatement strategies primarily target air quality improvement rather than mitigating ecological impacts. Given that the area with the risk of eutrophication induced by nitrogen deposition remained at 13% of the country even under the scenario of achieving the dual targets of air quality and carbon dioxide mitigation in 2035, we explored an enhanced ammonia abatement pathway. With a further 27% reduction in ammonia by 2035, China could largely eliminate the impacts of acid deposition. This research serves as a valuable reference for China's future acid deposition control and for other nations facing similar challenge.

How to cite: Yu, Q.: Atmospheric deposition and its impacts in China over the last four decades and beyond, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3034, https://doi.org/10.5194/egusphere-egu24-3034, 2024.

Ammonia emissions in China mainly came from agricultural activities. Excess emissions could lead to degraded air quality and excess nitrogen deposition. Therefore, it is essential to improve air quality and nitrogen deposition through agricultural ammonia reduction measures. On the basis of the existing research, this study established an Agricultural Management Technology-Ammonia emission assessment platform with 51 measures of fertilizer application and 53 measures of livestock farming derived from a literature review and adopted the Monte Carlo method to apply this platform to Beijing-Tianjing-Heibei (BTH) region where active agricultural activities occur. An updated agricultural ammonia emission inventory at 3-km resolution in BTH region was used in this study. 

We find that ammonia emissions from livestock farming could be reduced by 79-151Gg (30%-57%) and from fertilizer application by 58-163Gg (18%-51%) in BTH region in 2019. We applied two reduction scenarios that could achieve average and maximum ammonia emission reduction based on the Monte Carlo results, and evaluated the resulting improvements of air quality and deposition using the GCHP model with a resolution of 10km × 10km in BTH region.

The results show that the baseline of PM_2.5 concentration, NH_X and NO_y deposition in BTH region in 2019 is 27-61 µg/m³, 8-57 Gg N/month and 3-51 Gg N/month. Under two ammonia emission reduction scenarios, PM_2.5 concentration and NH_x deposition would, respectively, reduce 1.38-3.89 µg/m³, 3-14 Gg N/month while NO_y deposition would increase 0.5-2 Gg N/month. Our research shows that agricultural ammonia has great emission reduction potential that would benefit to the reduction of nitrogen pollution.

How to cite: Li, L., Zhang, L., Liu, X., Guo, Y., Xu, J., Ye, X., Li, D., and Liu, Z.: PM2.5 and nitrogen deposition mitigation under agricultural ammonia emission reduction in Beijing-Tianjin-Hebei region, China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7775, https://doi.org/10.5194/egusphere-egu24-7775, 2024.

Tropospheric ozone (O₃), a potent greenhouse gas and secondary air pollutant, stands out as a major photochemical pollutant, posing a considerable threat to plant life. Prolonged exposure to this gas triggers adverse changes in various plant parameters, hindering growth, and hastening senescence. This makes increasing ambient O₃ concentrations an urgent environmental concern. An essential aspect of addressing this issue lies in comprehending the mechanisms underlying O₃ resistance in plants, particularly for fostering sustainable urban greening in polluted environments. Certain indicative plant parameters, including morphological characteristics, and biochemical and antioxidant capacity, play pivotal roles in regulating the variation in O₃ resistance. However, the specific contributions of each trait remain somewhat elusive and understudied. Moreover, O₃ resistance exhibits significant variability within and across plant species, influenced by factors such as the timing of O₃ exposure and the plant's developmental stage. The present study delves into the nuances of O₃ sensitivity among four evergreen shrub species—Bougainvillea glabra, Buxus sempervirens, Duranta goldiana, and Ficus panda—that are commonly chosen for roadside plantations in Delhi. The selected species were exposed to elevated ozone concentrations, in a controlled fashion, in Open-Top Chambers (OTCs) for an entire growing season. The study examined changes in photosynthetic pigments (total chlorophyll, carotenoid), antioxidant capacity (ascorbic acid), and lipid peroxidation. The findings revealed significant discernible impacts of ozone fumigation alongside ambient air concentration. Compared to control samples (ambient air exposure conditions), under elevated ozone treatment, chlorophyll content and total carotenoid levels decreased substantially, while the ascorbic acid content and lipid peroxidation levels increased. Species that underwent the highest decrease in chlorophyll (C) content are the species that experienced the lowest increase in ascorbic acid (AA) levels, and vice versa (i.e., B. sempervirens [C-34.27%, AA+20.83%], D. goldiana [C-25%, AA+35.95%], F. panda [C-23.85%, AA+54.12%], and B. glabra [C-18%, AA+55.27%]). Based on the parametric changes observed in the considered species, it can be concluded that B. glabra is the most appropriate species (followed by F. panda) for systematic urban plantation in areas with high O₃ concentrations as it exhibited the highest tolerance. This research contributes valuable insights for selecting suitable plant species in ozone-polluted areas, facilitating environmentally conscious decision-making for the establishment of resilient and sustainable urban green spaces.

How to cite: Anand, P., Kota, S. H., and Mina, U.: Effects of Elevated Ozone Concentrations on Evergreen Shrubs in Delhi, India, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-398, https://doi.org/10.5194/egusphere-egu24-398, 2024.

We use the regional chemistry transport model WRF-Chem (v4.2.1) to analyse the sensitivity of surface dust across Northern India to various emissions' sources. We use idealised model experiments that switch off individual sources in an attempt to apportion dust aerosol concentrations to anthropogenic, biomass-burning, and natural dust sources. However, these experiments show significant non-linear interactions between sources, making simple apportionment difficult. Across the natural dust-dominated western part of the domain, we find that switching off anthropogenic emissions results in an increase in dust. Alternatively, this can be considered in the opposite sense: the presence of anthropogenic pollutants reduces surface dust aerosol concentrations by almost 50 % on average. We diagnose the processes responsible for this somewhat surprising result. Heterogeneous chemical reactions between dust and nitric acid (HNO₃) shorten the dust’s lifetime, increasing the sink for natural dust as HNO₃ is enhanced by anthropogenic NO_x emissions. The modelled dust lifetime is enhanced by nearly 4 hours when anthropogenic precursor emissions are excluded. The model shows a strong anticorrelation between dust and HNO₃, related to the preferential uptake of HNO₃ by dust particles over a broad relative humidity range (10 – 90 %). The strong non-linear response of dust loading to idealised emissions changes shows considerable regional variation. The effect of these dust-pollution interactions on dust lifetime suggest that dust concentrations will increase as anthropogenic NO_x emissions reduce, making control of particulate pollution harder, particularly in regions with high natural dust sources.

How to cite: Stevenson, D., Agarwal, P., Heal, M., and Zaveri, R.: Response of natural dust to removal of anthropogenic emissions over South Asia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11532, https://doi.org/10.5194/egusphere-egu24-11532, 2024.

Urban air pollution continues to pose a significant health threat, despite regulations to control emissions. Here we present a comparative analysis of the anthropogenic and meteorological drivers of surface ozone (O₃) change in China by integrating deep learning (DL) and chemical transport model (CTM) methods. The DL method suggests volatile organic compound (VOC)-limited regimes in urban areas over northern inland China in contrast to strong nitrogen oxides (NO_x)-limited regimes in GEOS-Chem simulations. Sensitivity analysis indicates that the inconsistent O₃ responses are partially caused by the inaccurate representation of O₃ precursor concentrations at the locations of urban air quality stations in the simulations. The DL method exhibits possible weakened anthropogenic contributions to surface O₃ rise in the North China Plain, for example, 1.53 and 0.54 ppb/y in 2015-2019 and 2019-2021, respectively. Similarly, GEOS-Chem simulations suggest an accelerated decrease in surface O₃ concentrations driven by the decline in nitrogen dioxide (NO₂) concentrations. Furthermore, both DL and GEOS-Chem models suggest the reverse of meteorological contributions to the observed O₃ change in the North China Plain in 2019-2021, which is mainly resulted from the reversed changes in meteorological variables in surface air temperature and relative humidity. This work highlights the importance of DL as a supplement to CTM-based analysis. The derived O₃ drivers are helpful for making effective regulatory policies to control O₃ pollution in China.

How to cite: Wang, M., Chen, X., He, T.-L., Jiang, Z., Liu, J., Liao, H., Jones, D., and Shen, Y.: Deep learning-derived anthropogenic and meteorological drivers of surface ozone change in China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7141, https://doi.org/10.5194/egusphere-egu24-7141, 2024.

Although the impacts of aviation NO_x on local air quality are well-researched, the effects on climate and global air quality are disputed. With the aviation sector under pressure to reduce its contributions to climate change, some studies have suggested that fuel efficiency be prioritized over reductions in aviation NO_x emissions. As a result, while emissions of NO_x have declined rapidly in other sectors, the amount of NO_x emitted per kilogram of aviation fuel burned is estimated to have increased by 17% between 1990 and 2018 with corresponding - and continuing - growth in environmental impact. We use a global atmospheric chemistry-transport model to simulate, at high resolution, the global air quality impacts of aviation, finding that emissions of cruise altitude NO_x specifically are associated with the majority of aviation's air quality impacts. Contrary to prior work we find that global simulation at high resolution (~50 km) results in an increase in the simulated impacts relative to simulations at low resolution (~400 km), and that - subject to the choice of epidemiological data source - aviation-attributable ozone may be responsible for global health impacts comparable in magnitude to the total national health burden of US combustion emissions. This presentation will explore the atmospheric mechanisms behind these effects, degree to which model resolution does or does not affect the simulated impacts, the implications for future aviation NO_x regulation, and the dominant sources of uncertainty in the result.

How to cite: Eastham, S., Chossière, G., Speth, R., Jacob, D., and Barrett, S.: Aviation NOx emissions and their increasing impact on global surface air quality, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11502, https://doi.org/10.5194/egusphere-egu24-11502, 2024.

In many parts of the world, ambient O₃ levels have increased despite regulatory efforts to improve O₃ air quality. The unexpectedly increasing O₃ levels are largely attributed to a lack of understanding about O₃ chemical regimes. The O₃ mitigation strategies related to precursor gas emission controls have not adequately considered the O₃ chemical regimes (NO_x-limited or VOC-limited conditions). This study develops a novel approach to identifying the spatiotemporal variations of O₃ chemical regimes collectively using ground and satellite data to support the decision-making of precursor gas emission controls. Using ground NO₂ and O₃ concentrations measured in both the Seoul Metropolitan Area (SMA) of the Republic of Korea and the LA County of California, U.S. for May 2018-April 2021, a mixed effects model is employed to generate daily relationships between NO₂ and O₃ concentrations. Positive and negative relationships between NO₂ and O₃ concentrations provide strong evidence of NO_x-limited and VOC-limited conditions, respectively. Satellite data on TROPOspheric Monitoring Instrument (TROPOMI) HCHO/NO₂ ratios represent relative NO_x-sensitivity or VOC-sensitivity (i.e., higher and lower ratios indicating increasing NO_x-sensitivity and VOC-sensitivity, respectively). The modeling and satellite approaches are complementary to each other because (1) the model does not account for VOC concentrations due to a lack of VOC measurements and (2) TROPOMI HCHO/NO₂ alone does not provide the threshold level of separating NO_x-limited from VOC-limited conditions. The monthly slopes of NO₂ concentrations against O₃ concentrations are highly correlated with monthly TROPOMI HCHO/NO₂ both in the SMA (0.75) and LA County (0.87). Threshold levels distinguishing NO_x- from VOC-limited conditions are defined by the TROPOMI HCHO/NO₂ values when the NO₂ slopes are equal to 0. In the SMA and LA County, the threshold levels are 3.0 (95% CI= 2.6-3.4) and 1.4 (95% CI= 1.3-1.6), respectively. During the study period, the O₃ chemical regime is mostly VOC-limited in the SMA (35 out of 36 months), meaning that NO_x emission controls can worsen O₃ air quality until the O₃ chemical regime reaches NO_x-limited conditions. In the SMA, VOC emission controls can help reduce the O₃ levels. On the other hand, in LA County, the O₃ chemical regimes transition from VOC-limited to NO_x-limited conditions during the warm seasons and vice versa during the cool seasons, depending on the seasonality of NO_x and VOC emissions. The O₃ mitigation strategies in LA County can be the most effective with season-specific emission controls. This study offers a novel method for determining the most effective strategy of precursor gas emission controls and informing decision-making to enhance O₃ air quality.

How to cite: Lee, H. J.: Developing a novel decision support tool for improving O3 air quality through strategic precursor gas emission controls, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5074, https://doi.org/10.5194/egusphere-egu24-5074, 2024.

China has been experiencing fast-paced urbanization and industrialization as well as stringent air pollution control in the past decades, which are expected to cause drastic changes in the anthropogenic emissions of primary air pollutants (e.g., SO₂, NOx and VOCs). Long-term observations are fundamental to the assessment of response of atmospheric composition to the changing anthropogenic emissions, which are, however, very limited in China. Here we integrated the observational data of trace gases and aerosol obtained during 2003-2023 at Mount Tai – the peak of the North China Plain (1534 m above sea level), a highly polluted region of China. The data were analyzed to understand the long-term changes of a variety of trace gases and aerosol properties such as ozone (O₃), PM_2.5 composition, particle number and size distribution, new particle formation and growth parameters, and O₃ depleting substances (ODS). Surface O₃ concentrations showed a significant increasing trend in summertime with a rate of ~2 ppbv yr^-1, despite the persistent decrease in NOx emissions since 2012, and can be attributed to the increasing VOCs and O₃ production efficiency. Sharp reduction in SO₂ emissions have resulted in significant decrease of sulfate in PM_2.5, whilst nitrate showed a strong increasing trend. A multi-phase chemical box model illustrated that the reduced SO₂ and sulfate enhanced nitrate formation by lessening the aerosol acidity and facilitating the partitioning of HNO₃ to the particle phase. The apparent formation rate of new particles in spring has increased at Mt. Tai, while the particle growth rate significantly decreased. The contributions of new particles to the cloud condensation nuclei (CCN) were also decreasing. The ODS regulated by the Montreal Protocol (MP) showed a significant downward trend, but the MP-controlled and unregulated halocarbon species showed overall upward trends. We will also present the results about the impacts of COVID lockdown on the regional air quality as observed at Mt. Tai.

How to cite: Xue, L., Wang, T., Gao, J., Chen, J., Zhu, Y., Wen, L., Li, H., Sun, L., Chen, T., Yang, L., Zhao, Y., Guo, Z., and Wang, W.: Trends of trace gases and aerosol over 2003-2023 at Mount Tai, northern China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2667, https://doi.org/10.5194/egusphere-egu24-2667, 2024.

Oil and gas account for more than two-thirds of energy consumed in the US. The high-temperature combustion from this use yields large quantities of nitrogen oxides (NO_x) that modulate the oxidative fate of isoprene, a precursor of health-hazardous air pollutants ozone, formaldehyde, and fine particulate matter (PM_2.5). The COVID-19 pandemic and resulting lockdowns provided a unique opportunity to examine changes in ozone and PM_2.5 linked to dramatic reduction in vehicle emissions. These occurred mostly in early spring when photochemistry is weak, biogenic emissions of isoprene are nascent, and ozone is titrated by vehicular nitric oxide (NO) emissions. Here, we use the 3D chemical transport model GEOS-Chem nested over contiguous US at a spatial resolution of 0.25º × 0.3125º (~28 km latitude × ~27 km longitude) to examine the complex influence of all oil and gas consumption or end-use activities on summertime (June-August) air pollutants in the eastern US where large cities, roadways and seasonal isoprene emission hotspots coincide. The model is driven with air pollutant precursor emissions for end-use activities from the US EPA National Emissions Inventory (NEI) for non-mobile sources and from the Fuel-based Inventory for Vehicular Emissions (FIVE) for mobile sources. We find that in the eastern US, end-use activities account for most NO_x (59% of NO and 57% of nitrogen dioxide, NO₂) and most (63% or 0.28 µg m^-3) aerosol-phase nitrate. As ammonia, predominantly from agricultural activity, buffers aerosol acidity, end-use activities also indirectly contribute to 21% (0.10 µg m^-3) of aerosol-phase ammonium. The influence on aerosol sulfate is negligible. NO from oil and gas end-use activities also modulates the proportion of isoprene that oxidizes via the NO and HO₂ pathways that in turn affects yields of formaldehyde and other reactive oxygenated volatile organic compounds (VOCs) as well as isoprene secondary organic aerosol (SOA) precursors. NO_x from oil and gas end-use activities enhances formaldehyde abundance by 0.3 ppb by increasing the proportion of isoprene reacting via the NO oxidation pathway that yields formaldehyde (and other oxygenated VOCs) promptly and in higher yields than the competing HO₂ (low-NO_x) oxidation pathway. This influence on reactive VOCs also adds 8 ppb of maximum daily mean 8-hour ozone, the metric used to assess the impact of ozone on health. Suppression of the HO₂ oxidation pathway and isoprene SOA precursors only decreases SOA by 0.02 µg m^-3. The net contribution of oil and gas end-use activities to PM_2.5 is 1.2 µg m^-3 or 12% of eastern US summertime mean PM_2.5. Our results suggest multiple, substantial improvements to summertime air quality by ending reliance on oil and gas.

How to cite: Vohra, K., Marais, E., Achakulwisut, P., Lu, G., Kelly, J., Francoeur, C., Harkins, C., and McDonald, B.: Secondary Effects of Oil and Gas End-Use on Summertime Air Pollutants in the Eastern US, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1134, https://doi.org/10.5194/egusphere-egu24-1134, 2024.

Atmospheric pollution is pointed out by the World Health Organization as the responsible for approximately 7 million premature deaths per year, and different approaches are investigated worldwide to reduce the high concentrations observed in urban areas. Regional-scale concentrations are influenced by different sources of pollutants, such as residences, industries and road traffic. Particularly road traffic is one of the important sources of regulated and emerging pollutants, including fine and ultra-fine particles, nitrogen dioxide and black carbon. Nevertheless, the traffic emission rate of each pollutant depends on the vehicle characteristics: the vehicle type, fuel and the vehicle manufacturing year. Urban mobility is, then, a key aspect to determine the total amount of traffic emissions, and choices related to the available modes of transport in a city may have an important role in urban air quality. This study investigates the influence of five extreme mobility scenarios on pollutant emissions and concentrations in urban air quality. In each scenario very strong limitations on road traffic are adopted: (i) a limited electrification of private and commercial vehicles and a shift to soft mobility, (ii) a significant increase in the number of users per car and reduced use of private cars car, (iii) a total electrification of the fleet (Paris-region target for 2030), (iv) limits on private vehicles circulation in specific areas, and (v) the implementation of all these measures simultaneously. For this, the regional-scale model CHIMERE is employed to calculate the concentrations of multi-pollutants with a 1 km x 1 km spatial resolution. A special focus is given to the emerging pollutants black carbon and ultra-fine particles. In this study CHIMERE is coupled with the chemical module SSH-aerosol, which enables the representation of aerosol dynamics with the state-of-art modules available in the literature. Simulations are performed in Paris during summer 2022. This study shows the potentialities of an air-quality modeling approach to understand trends in concentrations according to scenarios aiming to reduce population exposure to atmospheric pollution. 

How to cite: Lugon, L., Kemgne, C., Le Vot, V., Mauchard, N., Vu Quang, B., Wang, C., Vigneron, J., Dugay, F., Sanchez, O., and Sartelet, K.: Estimating the impact of mobility scenarios on urban air quality - a regional scale analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15311, https://doi.org/10.5194/egusphere-egu24-15311, 2024.

Understanding aerosol vertical distribution is of great importance to climate change and air quality management, but there is a dearth of systematical analysis for aerosol vertical distribution amid rapid emission decline after 2013 in China. Here, the GEOS-Chem model and multiple-sourced observations were applied to quantify the changes of aerosol vertical distributions in response to clean air actions. In 2013–2020, the MODIS aerosol optical depth (AOD) presented extensive decreasing trends by −7.9 %/yr to −4.2 %/yr in summer and −6.1 %/yr to −5.8%/yr in winter in polluted regions. Vertically, the aerosol extinction coefficient (AEC) from CALIPSO decreased by −8.0 %/yr to -5.5 %/yr below ~1 km, but the trends weakened significantly with increasing altitude. Compared with available measurements, the model can reasonably reproduce 2013–2020 trends and seasonality in AOD and vertical AECs. Model simulations confirm that emission reduction was the dominant driver of the 2013–2020 decline in AOD, while the effect of meteorology varied seasonally, with contributions ranging from −2% to 13% in summer and −67% to −2% in winter. Vertical distributions of emission-driven AEC trends strongly depended on emission reductions, local planetary boundary layer height, and relative humidity. For aerosol components, sulfate accounted for ~50% of the AOD decline during summer, followed by ammonium and organic aerosol, while in winter the contribution of organic aerosol doubled (24%–35%), and nitrate exhibited a weak increasing trend. Chemical production and meteorological conditions primarily drove the nitrate contribution, but emission reduction and hygroscopicity were decisive for other components. This work highlights the importance of integrating observational and modeling efforts to better understand rapid changes in aerosol vertical distribution over China.

How to cite: Chen, X., Li, K., Yang, T., Yang, Z., Wang, X., Zhu, B., Chen, L., Yang, Y., Wang, Z., and Liao, H.: Trends and drivers of aerosol vertical distribution over China from 2013 to 2020: Insights from integrated observations and modeling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2732, https://doi.org/10.5194/egusphere-egu24-2732, 2024.

The formation of secondary organic aerosols (SOA) is inextricably linked to the photo-oxidation of aromatic hydrocarbons. However, models still exhibit biases in representing the mass and chemical composition of SOA. We implemented a box model coupled with a near-explicit photochemical mechanism, the Master Chemical Mechanism (MCMv3.3.1) to simulate a series of chamber studies and access model biases in simulating SOA from representative aromatic hydrocarbons. The box model underpredicted SOA yields of toluene and xylenes by 4.7–100%, which could be improved by adjusting the saturation vapor pressure (SVP) of their oxidation products. After updating the SVP values, the mass concentration of TX SOA in the Yangtze River Delta region during summer was doubled, and there was also an approximated 3% enhancement in the total SOA. In comparison to a lumped mechanism used for simulating TX SOA, MCM predicted similar mass concentrations but exhibited different volatility distributions and oxidation states.

How to cite: Li, J., Lu, H., Huang, Q., Ying, Q., Qin, M., and Hu, J.: Simulation of Regional Secondary Organic Aerosol Formation From Monocyclic Aromatic Hydrocarbons using a Near-Explicit Chemical Mechanism Constrained by Chamber Experiments , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9640, https://doi.org/10.5194/egusphere-egu24-9640, 2024.

Secondary organic aerosol (SOA) formation from gasoline vehicles spanning a wide range in emission types was investigated using an oxidation flow reactor (OFR) by conducting chassis dynamometer tests. Aided by advanced mass spectrometric techniques, SOA precursors, including volatile organic compounds (VOCs), intermediate/semi-volatile organic compounds (I/SVOCs), were comprehensively characterized. The reconstructed SOA produced from the speciated VOCs and I/SVOCs can explain 69% of SOA measured downstream of OFR upon 0.5-3 days’ OH exposure. While VOCs can only explain 10% of total SOA production, contribution from I/SVOCs is 59%. We also found that oxygenated I/SVOCs (O–I/SVOCs, e.g., benzylic or aliphatic aldehydes and ketones), as an obscured source, accounted for 16% of total nonmethane organic gas (NMOG) emission and 20% of SOA production. More importantly, with the improvement in emission standards, the NMOG was effectively mitigated by 35% from China 4 to China 6, which is predominantly attributed to the decrease of VOCs. Real-time measurements of different NMOG components as well as SOA production further revealed that the current emission control measures, such as three-way catalytic converters (TWCs), are effective in reducing the “light” SOA precursors (i.e., single ring aromatics), but not for the I/SVOC emissions, indicating that the catalyst are selective upon reacting with different exhaust components. Our results highlight the neglected contribution from I/SVOCs, especially O-I/SVOCs to SOA formation and the urgent need in further investigation in their origins, i.e., incomplete combustion, lubricating oil, which requires improvements in real-time molecular-level characterization of I/SVOC molecules and in turn will benefit the future design of control measures.

How to cite: Huang, D. D., Hu, Q., He, X., Huang, R., Ding, X., Ma, Y., Feng, X., Jing, S., Li, Y., Lu, J., Gao, Y., Shi, X., Qian, C., Yan, C., Zhu, S., Lou, S., Wang, H., Fu, Q., Fu, Q., and Huang, C.: Obscured Contribution of Oxygenated Intermediate-Volatility Organic Compounds to Secondary Organic Aerosol Formation from Gasoline Vehicle Emissions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16035, https://doi.org/10.5194/egusphere-egu24-16035, 2024.