Surface Ozone Research Articles

The Influence of Meteorology Initialization on Ozone Forecasting in the Great Lakes Region during MOOSE Study

This study investigates the influence of meteorology initialization on surface ozone prediction in the Great Lakes region using Canada’s operational air quality model (GEM-MACH) at a 2.5 km horizontal resolution. Two different initialization techniques are compared, and it is found that the four-dimensional incremental analysis updating (IAU) method yields improved model performance for surface ozone prediction. The IAU run shows better ozone regression line statistics (y = 0.7x + 14.9, R2 = 0.2) compared to the non-IAU run (y = 0.6x + 23.1, R2 = 0.1), with improved MB and NMB values (3.9 ppb and 8.9%, respectively) compared to the non-IAU run (4.1 ppb and 9.3%). Furthermore, analyzing ozone prediction sensitivity to model initialization time reveals that the 18z initialization leads to enhanced performance, particularly during high ozone exceedance days, with an improved regression slope of 0.9 compared to 0.7 for the 00z and 12z runs. The MB also improves to −0.2 ppb in the 18z run compared to −2.8 ppb and −3.9 ppb for the 00z and 12z runs, respectively. The analysis of meteorological fields reveals that the improved ozone predictions at 18z are linked to a more accurate representation of afternoon wind speed. This improvement enhances the transport of ozone, contributing to the overall improvement in ozone predictions.

Assessment of surface ozone production in Qinghai, China with satellite-constrained VOCs and NOx emissions

The implementation of the western development strategy of China and the migration of air pollutants from eastern China might lead to a rapid increase in volatile organic compounds (VOCs) concentrations in the Qinghai-Tibet Plateau (QTP) and an amplified role of Nitrogen Oxides (NOx) in ozone (O3) pollution. Qinghai province, situated on the northeast of the QTP, had fewer human activities compared to eastern China, while ozone pollution worsened over the years. To better capture recent emission trends and improve the accuracy of O3 simulation in Qinghai, this study proposed a top-down method, which combined the air quality modeling system RAMS-CMAQ, with formaldehyde (HCHO) and nitrogen dioxide (NO2) columns derived from TROPOMI as the constraints to improve the emission estimates of VOCs and NOx in July 2020, respectively. Through a series of sensitivity experiments, better quantified emission estimates of VOCs and NOx were obtained to be 1.33 and 0.34 Tg/yr, 2.5 and 2.1 times larger than the bottom-up ones. The results demonstrated the effectiveness of the top-down method and satellite observations constraints in improving VOCs and NOx emission estimates, resulting in a reduction in the differences between the observed and modeled HCHO and NO2 columns to 0.7 and 0.2 × 1015 molec/cm2, respectively. As a result, the simulated maximum daily 8-h average (MDA8) O3 concentrations increased from 58.9 to 81.6 μg/m3, which were closer to observations (85.4 μg/m3), the normalized mean bias (NMB) and normalized mean error (NME) values of hourly O3 concentrations changed from −24.7 % to −2.9 % and from 29.9 % to 22.3 %, respectively. This study showed the potential of top-down estimates to aide in the development of emission scenarios, which were critical for accurately simulating the O3 pollution and pollution control policy studies.

Effects of Elevated Surface Ozone Concentration on Photosynthetic Fluorescence Characteristics and Yield of Soybean Parents and Offspring

Global climate change presents a significant threat to food security. Analyzing the effects of elevated ozone (O3) concentration on photosynthetic fluorescence characteristics and yield addresses the damage of climate change on crops, which would serve food security. With open-top chambers (OTCs) and Tiefeng-29 soybeans, we investigated the responses of chlorophyll concentration, fluorescence characteristics, net photosynthetic rate (Pn) and yield components to different O3 concentrations, which included CK (ambient concentration approximately 45 nL·L−1, T1 (80 ± 10) nL·L−1 and T2 (120 ± 10) nL·L−1 O3. The parent soybeans (S1) were planted in the current year, and O3 fumigation commenced 20 days after seedling emergence. Aeration was stopped at maturity, and the offspring soybeans (S2) were retained after harvest for further experiments. In the following year, S1 and S2 soybeans were planted, and O3 fumigation began 20 days after seedling emergence. The results show that leaf chlorophyll a (chla) and chlorophyll b (chlb) significantly decreased with longer O3 fumigation time both in parents and offspring, causing damage to the light-trapping ability while the offspring suffered an earlier decrease. The elevated O3 damaged the electron transfer process by significantly reducing the original and actual photochemical efficiencies of PSII both in parents and offspring. The electron transfer rate (ETR) of the parents and offspring decreased, while the difference between them was not significant after O3 treatment. The non-photochemical quenching coefficient (NPQ) showed an increasing trend along time but showed no significant difference between parents and offspring. An elevated concentration of O3 significantly reduced Pn, while the differences in Pn between the parents and the offspring were not significant. Elevated O3 resulted in reduced yields in both parent and offspring soybeans. Although it was found that the offspring soybeans exhibited higher yields than the parents, their reduction in yield was more significant. Therefore, elevated O3 concentration reduced soybean yield through damaging photosynthetic process and electron transfer capacity by impairing energy conversion and material accumulation capacity. The offspring had relatively higher light energy conversion efficiency than the parents, resulting in a higher yield than the parents under all treatments.

Ozone deterioration over North China plain caused by light absorption of black carbon and organic carbon

Previous studies have revealed that the light absorption effect of black carbon (BC) aerosol could influence ozone concentrations via absorbing sunlight and modulating photolysis rates, the so-called aerosol-photolysis interaction (API). However, few studies have quantified the API effect of organic carbon (OC) aerosol, which has recently been found to contribute to about 10%–40% of the total light absorption at 300 nm wavelength. This study tried to quantify and compare the OC and BC aerosols' influence on ozone concentrations through a case study over North China Plain (NCP) in Oct. 2018. By modulating OC's absorption index based on field measurements, we quantified the OC and BC API effect on surface ozone by the WRF-Chem model. The API effect and its uncertainties of OC aerosols were evaluated using the high and low absorption values that have been reported in previous studies. Results showed that, in terms of the pollution periods in NCP, removing all the OC aerosol from the atmosphere could increase the daytime maximum daily average 8-h (MDA8) O3. In this episode, the average (extreme) MDA8 O3 increased by 0.7–2.4 ppb (1.1–3.7 ppb), accounting for 1.5%–5.3% (2.4%–8.8%) of ozone concentration, comparable to that by BC of 2.0 ppb (3.3 ppb), accounting for 4.4% (7.8%), which means the OC's API effect was 35%–120% of BC's API effect on surface ozone in this case. The results also indicated a fact that, though OC has a lower light absorption rate than BC, the API efficiency of OC on surface ozone when reducing aerosols could be compensated by a higher portion of OC aerosols and higher light absorption efficiency due to much more OC was distributed on higher altitude (especially 1–3 km) than BC aerosols, which result in larger ozone changes in both the low troposphere and surface.

Sensitivity of northeastern US surface ozone predictions to the representation of atmospheric chemistry in the Community Regional Atmospheric Chemistry Multiphase Mechanism (CRACMMv1.0).

Chemical mechanisms describe how emissions of gases and particles evolve in the atmosphere and are used within chemical transport models to evaluate past, current, and future air quality. Thus, a chemical mechanism must provide robust and accurate predictions of air pollutants if it is to be considered for use by regulatory bodies. In this work, we provide an initial evaluation of the Community Regional Atmospheric Chemistry Multiphase Mechanism (CRACMMv1.0) by assessing CRACMMv1.0 predictions of surface ozone (O3) across the northeastern US during the summer of 2018 within the Community Multiscale Air Quality (CMAQ) modeling system. CRACMMv1.0 O3 predictions of hourly and maximum daily 8 h average (MDA8) ozone were lower than those estimated by the Regional Atmospheric Chemistry Mechanism with aerosol module 6 (RACM2_ae6), which better matched surface network observations in the northeastern US (RACM2_ae6 mean bias of +4.2 ppb for all hours and +4.3 ppb for MDA8; CRACMMv1.0 mean bias of +2.1 ppb for all hours and +2.7 ppb for MDA8). Box model calculations combined with results from CMAQ emission reduction simulations indicated a high sensitivity of O3 to compounds with biogenic sources. In addition, these calculations indicated the differences between CRACMMv1.0 and RACM2_ae6 O3 predictions were largely explained by updates to the inorganic rate constants (reflecting the latest assessment values) and by updates to the representation of monoterpene chemistry. Updates to other reactive organic carbon systems between RACM2_ae6 and CRACMMv1.0 also affected ozone predictions and their sensitivity to emissions. Specifically, CRACMMv1.0 benzene, toluene, and xylene chemistry led to efficient NO x cycling such that CRACMMv1.0 predicted controlling aromatics reduces ozone without rural O3 disbenefits. In contrast, semivolatile and intermediate-volatility alkanes introduced in CRACMMv1.0 acted to suppress O3 formation across the regional background through the sequestration of nitrogen oxides (NO x ) in organic nitrates. Overall, these analyses showed that the CRACMMv1.0 mechanism within the CMAQ model was able to reasonably simulate ozone concentrations in the northeastern US during the summer of 2018 with similar magnitude and diurnal variation as the current operational Carbon Bond (CB6r3_ae7) mechanism and good model performance compared to recent modeling studies in the literature.

Soil Emissions of Reactive Nitrogen Accelerate Summertime Surface Ozone Increases in the North China Plain.

Summertime surface ozone in China has been increasing since 2013 despite the policy-driven reduction in fuel combustion emissions of nitrogen oxides (NOx). Here we examine the role of soil reactive nitrogen (Nr, including NOx and nitrous acid (HONO)) emissions in the 2013-2019 ozone increase over the North China Plain (NCP), using GEOS-Chem chemical transport model simulations. We update soil NOx emissions and add soil HONO emissions in GEOS-Chem based on observation-constrained parametrization schemes. The model estimates significant daily maximum 8 h average (MDA8) ozone enhancement from soil Nr emissions of 8.0 ppbv over the NCP and 5.5 ppbv over China in June-July 2019. We identify a strong competing effect between combustion and soil Nr sources on ozone production in the NCP region. We find that soil Nr emissions accelerate the 2013-2019 June-July ozone increase over the NCP by 3.0 ppbv. The increase in soil Nr ozone contribution, however, is not primarily driven by weather-induced increases in soil Nr emissions, but by the concurrent decreases in fuel combustion NOx emissions, which enhance ozone production efficiency from soil by pushing ozone production toward a more NOx-sensitive regime. Our results reveal an important indirect effect from fuel combustion NOx emission reduction on ozone trends by increasing ozone production from soil Nr emissions, highlighting the necessity to consider the interaction between anthropogenic and biogenic sources in ozone mitigation in the North China Plain.

Correlation between air temperature and surface ozone in their extreme ranges in the greater Tokyo region

High-level ozone (O3) events observed around major urban regions in the middle latitudes are correlated with high temperatures (T-O3 correlation). Therefore, the effects of global warming on the future O3 levels are a matter of concern. The T-O3 correlation is caused by various physicochemical and meteorological processes, the importance of which can differ by region. This statistical analysis focused on the correlation in the extremely high ranges, because the lower ranges would only act as noise in elucidating the conditions at which high temperatures and high levels of O3 occur. This methodology was applied to the greater Tokyo region after 2001, where severe O3 events frequently occurred when the sea breeze system developed in summer. To select sample days for the analysis, this study set up twofold filtering: (1) a large threshold for midday sunshine duration and (2) a typical variation pattern to roughly judge sea breeze days, mostly essential weather pattern for high-level O3 events in the region. The most notable result was a decrease in O3 corresponding to the reduction in non-methane hydrocarbons (NMHC) from Period I (2001–2007) to Period III (2017–2019). As the NMHC rank reduced, the linear regression line for the T-O3 correlation shifted downward, but its slope (ppb/°C) remained around 10, except that temporary spikes in O3 levels and temperatures occurred at moderate NMHC levels. From an urban meteorological perspective, the wind speed in the mature stage of the sea breeze is the major factor behind the T-O3 correlation.

Rebuilding high-quality near-surface ozone data based on the combination of WRF-Chem model with a machine learning method to better estimate its impact on crop yields in the Beijing-Tianjin-Hebei region from 2014 to 2019

In recent years, the problem of surface ozone pollution in China has been of great concern. According to observation data from monitoring stations, the concentration of near-surface ozone (O3) in China has gradually increased in recent years, and ozone concentration often exceeds the contaminant limit standard, especially in the Beijing-Tianjin-Hebei (BTH) region. High O3 concentration pollution will adversely affect crop growth, which can cause crop yield losses. Therefore, it is urgent to recognize the situation of ozone pollution in the BTH region and quantitatively evaluate the crop yield losses caused by ozone pollution to develop more effective pollution prevention and control policies. However, the monitoring of ozone concentration in China started relatively late compared with some developed countries, and currently, long-time series data covering the BTH region cannot be obtained, which makes it difficult to evaluate the impact of ozone on crop yield. Therefore, a new method (WRFC-XGB) was proposed in this study to establish a high-precision near-surface O3 concentration dataset covering the whole BTH region from 2014 to 2019 by integrating the Weather Research and Forecasting with Chemistry (WRF-Chem) model with the extreme gradient boosting (XGBoost) machine learning algorithm. Through verification with ground observation station data, the results of WRFC-XGB are satisfactory, and R2 can reach 0.78–0.91. Compared with other algorithms, the accuracy of the near-surface ozone concentration dataset is greatly improved, which can be used to estimate the impact of surface ozone on crop yield. Based on this dataset, the yield loss of winter wheat, rice, and maize caused by O3 pollution was estimated by using the response equation of the relative yield and ozone dose index. The results showed that the total yield losses of winter wheat, rice and maize from 2014 to 2019 were 2659.21 million tons, 49.23 million tons and 1721.56 million tons due to ozone pollution in the BTH region, respectively, and the highest relative yield loss of crops caused by O3 pollution could be 29.37% during 2014–2019, which indicated that the impact of ozone pollution on crop yield cannot be ignored, and effective measures need to be developed to control ozone pollution, prevent crop production loss, and ensure people's food security.

Contrasting effects of clean air actions on surface ozone concentrations in different regions over Beijing from May to September 2013–2020

Due to the nonlinear impacts of meteorology and precursors, the response of ozone (O3) trends to emission changes is very complex over different regions in megacity Beijing. Based on long-term in-situ observations at 35 air quality sites (four categories, i.e., urban, traffic, northern suburban and southern suburban sites) and satellite data, spatiotemporal variability of O3, gaseous precursors, and O3-VOCs-NOx sensitivity were explored through multiple metrics during the warm season from 2013 to 2020. Additionally, the contribution of meteorology and emissions to O3 was separated by a machine-learning-based de-weathered method. The annual averaged MDA8 O3 and O3 increased by 3.7 and 2.9 μg/m3/yr, respectively, with the highest at traffic sites and the lowest in northern suburb, and the rate of Ox (O3 + NO2) was 0.2 μg/m3/yr with the highest in southern suburb, although NO2 declined strongly and HCHO decreased slightly. However, the increment of O3 and Ox in the daytime exhibited decreasing trends to some extent. Additionally, NOx abatements weakened O3 loss through less NO titration, which drove narrowing differences in urban-suburban O3 and Ox. Due to larger decrease of NO2 in urban region and HCHO in northern suburb, the extent of VOCs-limited regime fluctuated over Beijing and northern suburb gradually shifted to transition or NOx-limited regime. Compared with the directly observed trends, the increasing rate of de-weathered O3 was lower, which was attributed to favorable meteorological conditions for O3 generation after 2017, especially in June (the most polluted month); whereas the de-weathered Ox declined except in southern suburb. Overall, clean air actions were effective in reducing the atmospheric oxidation capacity in urban and northern suburban regions, weakening local photochemical production over Beijing and suppressing O3 deterioration in northern suburb. Strengthening VOCs control and keeping NOx abatement, especially in June, will be vital to reverse O3 increase trend in Beijing.

Changes in Ozone Pollution Trend Characteristics and Sensitivity in Jinan from 2015 to 2020

The surface ozone (O3) spatiotemporal distribution, variations, and its causes in Ji'nan from 2015 to 2020 were revealed based on the air quality monitoring network data and satellite retrievals from the Ozone Monitoring Instrument (OMI). The results showed that the ozone concentration in Ji'nan gradually increased from 2015 to 2020. The annual 90th percentile of the daily maximum 8-h average (MDA8) O3(namely the annual evaluation value) and the MDA8 O3(April-September) increased by 4.8 μg·(m3·a)-1 and 3.8 μg·(m3·a)-1, respectively. The trend of the ozone levels in the high-concentration range increased faster than that in the low-concentration range. The MDA8 in June increased by 7.4 μg·(m3·a)-1, and the rate range of increases was 2.6-3.9 μg·(m3·a)-1 in the cool seasons (December-February); thus, the O3 control in winter cannot be ignored. It is apparent from the diurnal variations in ozone from 2015 to 2020 in April-September that the average ozone levels have risen in recent years. The growth rate in the daytime was higher than that at night. The capacity of photochemical production has been increasing, especially in recent years. Additionally, it is noteworthy that the peak time for ozone levels occurred approximately 1-2 h earlier. The disparity of ozone concentrations among different stations gradually decreased in recent years. Compared with that in 2015, the range of areas with high O3 concentrations in 2019-2020 was further expanded. The significant positive trends in MDA8-90th and MDA8 (April-September) were observed in 16.1% and 22.6% of the monitoring sites in Ji'nan (P<0.05), most of which were located in urban areas and the suburbs close to urban areas. The temporal and spatial changes in ozone in Jinan had been affected by the changes in VOCs and NOx emissions since 2015. Satellite remote sensing data from 2015 to 2020 revealed that the NO2 tropospheric columns (April-September) showed reductions of 20.6%, with a decreasing rate of 0.3×1015 mole·(cm2·a)-1, especially in the urban areas and suburbs. The detected variation trends of tropospheric HCHO were weak and insignificant, which suggested that the decrease in NOx emissions was much greater than the decrease in VOCs emissions, and the gap had become more obvious in the urban areas. With responses to precursor emissions, the chemical sensitivity of O3 formation had been changing. The VOCs-limited regimes continuously decreased, and the mixed NOx/VOCs-sensitive regimes and NOx-limited regimes increased. In general, such an extremely inappropriate control ratio of ozone precursor NOx/VOCs led to an overall trend of slow increasing fluctuations of O3 in Ji'nan. The findings clearly indicate that the reduction of VOCs in Ji'nan was far from sufficient, and strengthening the current control of VOCs emissions is an effective measure to control the growth trend of O3 pollution in Ji'nan in the near future, especially in urban and surrounding suburban areas.

Analysis of O3 Pollution Characteristics, Formation Sensitivity, and Transport Impact in Southern Nanjing

As one of the most important city clusters in China, surface ozone (O3) pollution in the Yangtze River Delta (YRD) Region has become a prominent air quality problem in recent years. Online observations of ambient O3, nitrogen oxides (NOx), and volatile organic compounds (VOCs) were conducted in southern Nanjing from July-September 2020 and April-May 2021. On this basis, the pollution characteristics of O3 were analyzed. The O3-VOCs-NOx sensitivity and the transport influence of its precursors were further discussed using models. The frequency statistics of the daily maximum 8-hour moving average (DMA-8h O3) and hourly concentration (O3-1h) showed that O3 pollution in southern Nanjing was more serious than that in urban areas. Three typical O3 pollution episodes were selected during the whole observation period, which included August 16th-27th, 2020; September 3rd-11th, 2020; and May 17th-25th, 2021. The O3-VOCs-NOx sensitivities in these three pollution episodes were analyzed using the observation-based model (OBM). The results of the relative incremental reactivity (RIR) and empirical kinetics modeling approach (EKMA) showed that the sensitivities of O3 formation in the three pollution episodes were in the NOx-limited regime, the transition regime, and the VOCs-limited regime, respectively. This difference in O3-VOCs-NOx sensitivity reflects that the site may have been influenced by transport. Therefore, the potential source contribution function (PSCF) and the concentration weighted trajectory (CWT) method were further used to analyze the potential source areas of NOx, VOCs, and O3 in these three pollution episodes. The results showed that there were obvious regional transport effects of NOx, VOCs, and O3 in these three pollution episodes. The location of potential sources differed in these three pollution episodes, which were affected by the eastern cities of the Lishui site; the urban area of Nanjing and eastern area of Anhui Province; and the urban area of Nanjing and the middle of the YRD Region, respectively. The impact of transport on O3 and its precursors also indicated the necessity of regional joint prevention and control of O3 pollution in the YRD Region.

High Spatial Resolution Ozone Profiles Retrieved from the First Chinese Ultraviolet–Visible Hyperspectral Satellite Instrument

Understanding the vertical distribution of ozone is crucial when assessing both its horizontal and vertical transport, as well as when analyzing the physical and chemical properties of the atmosphere. One of the most effective ways to obtain high spatial resolution ozone profiles is through satellite observations. The Environmental Trace Gases Monitoring Instrument (EMI) deployed on the Gaofen-5 satellite is the first Chinese ultraviolet–visible hyperspectral spectrometer. However, retrieving ozone profiles using backscattered radiance values measured by the EMI is challenging due to unavailable measurement errors and a low signal-to-noise ratio. The algorithm developed for the Tropospheric Monitoring Instrument did not allow us to retrieve 87% of the EMI pixels. Therefore, we developed an algorithm specific to the characteristics of the EMI. The fitting residuals are smaller than 0.3% in most regions. The retrieved ozone profiles were in good agreement with ozonesonde data, with maximum mean biases of 20% at five latitude bands. By applying EMI averaging kernels to the ozonesonde profiles, the integrated stratospheric column ozone and tropospheric column ozone also showed excellent agreement with ozonesonde data. The lower layers (0–7.5 km) of the EMI ozone profiles reflected the seasonal variation in surface ozone derived from the China National Environmental Monitoring Center (CNEMC). However, the upper layers (9.7–16.7 km) of the ozone profiles show different trends, with the ozone peak occurring at an altitude of 9.7–16.7 km in March, 2019. A stratospheric intrusion event in central China from August 11 to 15, 2019, is captured using the EMI ozone profiles, potential vorticity data, and relative humidity data. The increase in the CNEMC ozone concentration showed that downward transport enhanced surface ozone pollution.

Application of Satellite‐Based Detections of Arctic Bromine Explosion Events Within GEOS‐Chem

AbstractDuring polar spring, periods of elevated tropospheric bromine drive near complete removal of surface ozone. These events impact the tropospheric oxidative capacity and are an area of active research with multiple approaches for representing the underlying processes in global models. We present a method for parameterizing emissions of molecular bromine (Br2) over the Arctic using satellite retrievals of bromine monoxide (BrO) from the Ozone Monitoring Instrument (OMI). OMI retrieves column BrO with daily near global coverage, and we use the GEOS‐Chem chemical mechanism, run online within the Goddard Earth Observing System Earth System Model to identify hotspots of BrO likely associated with polar processes. To account for uncertainties in modeling background BrO, hotspots are only identified where the difference between OMI and modeled columns exceeds a statistical threshold. The resulting hotspot columns are a lower‐limit for the portion of OMI BrO attributable to bromine explosion events. While these hotspots are correlated with BrO measured in the lower troposphere over the Arctic Ocean, a case study of missing detections of near‐surface BrO is identified. Daily flux of Br2 is estimated from hotspot columns of BrO using internal model parameters. When the emissions are applied, BrO hotspots are modeled with a 5% low bias. The sensitivity of the resulting ozone simulations to the treatment of background uncertainties in the BrO column is demonstrated. While periods of isolated, large (&gt;50%) decreases in surface ozone are modeled, this technique does not simulate the low ozone observed at coastal stations and consistently underestimates ozone loss during March.

The Air Pollution Human Health Burden in Different Future Scenarios That Involve the Mitigation of Near-Term Climate Forcers, Climate and Land-Use.

Elevated surface concentrations of ozone and fine particulate matter (PM2.5) can lead to poor air quality and detrimental impacts on human health. These pollutants are also termed Near-Term Climate Forcers (NTCFs) as they can also influence the Earth's radiative balance on timescales shorter than long-lived greenhouse gases. Here we use the Earth system model, UKESM1, to simulate the change in surface ozone and PM2.5 concentrations from different NTCF mitigation scenarios, conducted as part of the Aerosol and Chemistry Model Intercomparison Project (AerChemMIP). These are then combined with relative risk estimates and projected changes in population demographics, to estimate the mortality burden attributable to long-term exposure to ambient air pollution. Scenarios that involve the strong mitigation of air pollutant emissions yield large future benefits to human health (25%), particularly across Asia for black carbon (7%), when compared to the future reference pathway. However, if anthropogenic emissions follow the reference pathway, then impacts to human health worsen over South Asia in the short term (11%) and across Africa (20%) in the longer term. Future climate change impacts on air pollutants can offset some of the health benefits achieved by emission mitigation measures over Europe for PM2.5 and East Asia for ozone. In addition, differences in the future chemical environment over regions are important considerations for mitigation measures to achieve the largest benefit to human health. Future policy measures to mitigate climate warming need to also consider the impact on air quality and human health across different regions to achieve the maximum co-benefits.

The Large-Scale Atmospheric Circulation Pattern over Asia Associated with Formation of Extremely High Surface Ozone Concentrations in the Region of Tomsk (Western Siberia)

The Large-Scale Atmospheric Circulation Pattern over Asia Associated with Formation of Extremely High Surface Ozone Concentrations in the Region of Tomsk (Western Siberia)

Significant land cover change in China during 2001–2019: Implications for direct and indirect effects on surface ozone concentration

China has become one of the most prominent areas of global land cover change during the past few decades. These changes can directly influence meteorological parameters thus further regulating tropospheric ozone (O3) formation. Moreover, changes in biogenic emissions due to land cover variation can also have an indirect effect on O3 concentration. This study applied the Community Multiscale Air Quality model to comprehensively evaluate the impacts of significant land cover change on O3 levels in China during summertime between 2001 and 2019. The results showed that the daily maximum 8–h average O3 concentration (MDA8 O3) increased by 3.6–8.9 μg/m3, 2.8–8.0 μg/m3, 3.8–9.6 μg/m3, -1.5–6.2 μg/m3, and -0.6–2.5 μg/m3 in Beijing–Tianjin–Hebei region, Yangtze River Delta, Pearl River Delta, Sichuan Basin, and Fenwei Plain, respectively, in response to land cover variation. The research identified that the direct effect was the primary factor in raising O3 levels which mainly altered O3 concentration by changing vertical import and dry deposition velocity. Moreover, land cover variation tended to decrease biogenic nitric oxide emission and increase biogenic volatile organic compounds emission on the whole, and cause an obvious increase of MDA8 O3 by 1.8–4.9 μg/m3 in Pearl River Delta due to the indirect effect. This study offered valuable insights into the impacts of land cover change on O3 levels, highlighting the need for policymakers to consider land cover variation on air pollutants concentration for devising comprehensive multi-pollutant control strategies.

A comprehensive approach combining positive matrix factorization modeling, meteorology, and machine learning for source apportionment of surface ozone precursors: Underlying factors contributing to ozone formation in Houston, Texas

Ozone concentrations in Houston, Texas, are among the highest in the United States, posing significant risks to human health. This study aimed to evaluate the impact of various emissions sources and meteorological factors on ozone formation in Houston from 2017 to 2021 using a comprehensive PMF-SHAP approach. First, we distinguished the unique sources of VOCs in each area and identified differences in the local chemistry that affect ozone production. At the urban station, the primary sources were n_decane, biogenic/industrial/fuel evaporation, oil and gas flaring/production, industrial emissions/evaporation, and ethylene/propylene/aromatics. At the industrial site, the main sources were industrial emissions/evaporation, fuel evaporation, vehicle-related sources, oil and gas flaring/production, biogenic, aromatic, and ethylene and propylene. And then, we performed SHAP analysis to determine the importance and impact of each emissions factor and meteorological variables. Shortwave radiation (SHAP values are ∼5.74 and ∼6.3 for Milby Park and Lynchburg, respectively) and humidity (∼4.87 and ∼4.71, respectively) were the most important variables for both sites. For the urban station, the most important emissions sources were n_decane (∼2.96), industrial emissions/evaporation (∼1.89), and ethylene/propylene/aromatics (∼1.57), while for the industrial site, they were oil and gas flaring/production (∼1.38), ethylene/propylene (∼1.26), and industrial emissions/evaporation (∼0.95). NOx had a negative impact on ozone production at the urban station due to the NOx-rich chemical regime, whereas NOx had positive impacts at the industrial site. The study's findings suggest that the PMF-SHAP approach is efficient, inexpensive, and can be applied to other similar applications to identify factors contributing to ozone-exceedance events. The study's results can be used to develop more effective air quality management strategies for Houston and other cities with high levels of ozone.

The impact of extremely high levels of PM2.5 on surface ozone during massive dust storms

Large amounts of Particulate Matter (PM) produced by dust storms can have adverse effects on health. When inhaled, PM2.5 (PM having a diameter of 2.5 ​μm or smaller) can cause serious respiratory problems in young children and the elderly. Despite of these adverse impacts dust storms can help remove gaseous pollutants through dry deposition. Thus, the aim of this study is to show the temporal variation of the monitored PM2.5 and to identify its effect on ozone (O3) during dust storms. In 2015 massive dust storms blowing from southern deserts in Iran and Saudi Arabia hit many areas in the Gulf region including the Sultanate of Oman. In the Sohar region these storms were the biggest in over a decade and caused extremely high levels of PM2.5 that exceeded 350 ​μgm−3 and reached up to 1884 ​μgm−3. Impressively it was found that dust storms reduced the concentrations of the precursors of surface ozone (NO, NO2, NOx); (correlation coefficients; −0.53, −0.69, and −0.67, respectively). Accordingly, for air quality management, in areas with similar and frequent conditions, international air quality guidelines and standards from both World Health Organization (WHO) and the U.S. Environmental Protection Agency (USEPA) are inappropriate. Thus, in Arabian Gulf countries, where people spend more time indoors, it is necessary to set national guidelines for managing air quality by considering local environmental conditions.

Ozone variability driven by the synoptic patterns over China during 2014–2022 and its implications for crop yield and economy

China has experienced increasingly serious ozone (O3) pollution in recent years, posing a great threat to agricultural ecosystem and economy. In this study, the decadal records of surface ozone concentrations across China (2014–2022), combined with the spatial synoptic classification (SSC) and multiple linear regression (MLR) methods are used to determine the surface ozone variability driven by the synoptic weather patterns. The maximum daily average 8-h (MDA8) ozone concentrations increase significantly from 2014 to 2019 at 2.5–5.2 μg m−3 yr−1 and decrease over the years 2019–2021, with a rebound in 2022. Strong connections between surface O3 levels and SSC synoptic weather patterns are identified, with the dry tropical (DT) weather pattern featured by dry and hot air masses as the main contributor to 35.3% of the high ozone occurrences and partly explaining the observed ozone trends in recent decade (e.g., +9.7% ozone increase per tripling of the DT frequency). Quantitative MLR analysis further confirms that meteorological conditions play an important role in the seasonal ozone trends from 2014 to 2022 (up to a 28.6% contribution), and daily-maximum air temperature and solar radiation could explain 11.3–51.0% and 11.1–37.4% of the meteorological-driven ozone trends. Using the agricultural statistical data and empirical algorithms, it is estimated that the annual yields of winter wheat, single-cropping rice, double-cropping early rice and late rice are reduced by 9.0–17.0%, 6.0−8.2%, 4.8−9.4% and 3.9−7.0%, respectively, in China during 2014–2022 due to the ozone exposure, along with a total economic loss of 74.9–171.9 billion yuan per year. This study is meaningful to understand the driving factors for the increasingly serious ozone pollution and is beneficial for the synergetic control of air pollution and climate mitigation.

Surface ozone risk to human health and vegetation in tropical region: The case of Thailand

Tropospheric ozone (O3) is a threat to vegetation and human health over the world, in particular in Asia. Knowledge on O3 impacts on tropical ecosystems is still very limited. An O3 risk assessment to crops, forests, and people from 25 monitoring stations across the tropical and subtropical Thailand during 2005–2018 showed that 44% of sites exceeded the critical levels (CLs) of SOMO35 (i.e., the annual Sum Of daily maximum 8-h Means Over 35 ppb) for human health protection. The concentration-based AOT40 CL (i.e., sum of the hourly exceedances above 40 ppb for daylight hours during the assumed growing season) was exceeded at 52% and 48% of the sites where the main crops rice and maize are present, respectively, and at 88% and 12% of the sites where evergreen or deciduous forests are present, respectively. The flux-based metric PODY (i.e., Phytotoxic Ozone Dose above a threshold Y of uptake) was calculated and was found to exceed the CLs at 1.0%, 1.5%, 20.0%, 1.5%, 0% and 68.0% of the sites where early rice, late rice, early maize, late maize, evergreen forests, and deciduous forests can grow, respectively. Trend analysis indicated that AOT40 increased over the study period (+5.9% year−1), while POD1 decreased (- 5.3% year−1), suggesting that the role of climate change in affecting the environmental factors that control stomatal uptake cannot be neglected. These results contribute novel knowledge on O3 threat to human health, forest productivity, and food security in tropical and subtropical areas.