Variations Of O3 Research Articles

Variations in air pollution before, during and after the COVID-19 lockdown in Peruvian cities.

The high concentrations of air pollutants in Peru remain a persistent problem, significantly impacting public health. Understanding the extent to which the COVID-19 lockdown affected these contaminants is crucial. To determine variations in NO2, O3, CO, and SO2 concentrations in 10 Peruvian cities before, during, and after lockdown. A comparative ecological study was conducted in urban areas of 10 major Peruvian cities using the Google Earth Engine (GEE) platform. Data on atmospheric pollutant concentrations were extracted from the Sentinel-5P/TROPOMI satellite images for the period between March 16 and June 30, across the years 2019, 2020, 2021, and 2022, for comparative analysis. The Wilcoxon test was used to evaluate changes between the study periods. We included 10 urban cities located across three geographic regions of Peru. Most urban cities experienced a decrease in NO2 concentrations and an increase in O3 and CO levels during the lockdown, while SO2 concentrations remained relatively constant. The lockdown has caused variations in NO2, O3 and CO concentrations. Future studies with accurate data on air pollutant concentrations are needed to ensure targeted and effective interventions.

Diurnal hourly near-surface ozone concentration derived from geostationary satellite in China

Near-surface O3 is a harmful atmospheric pollutant and a key component of urban photochemical pollution. The availability of satellite ozone concentration products is predominantly restricted to daytime, resulting in a lack of understanding of nighttime ozone pollution (e.g. nocturnal ozone enhancement events). This research leverages 5-km bright temperatures derived from Advanced Himawari Images (AHI) on the Himawari-8 satellite, in conjunction with auxiliary data, to estimate 24-h near-surface O3 concentrations in China at a resolution of 5 km for 2020. The model achieves an average 5-fold cross-validation R2 of 0.92. Comparative analysis with on-site observations reveals that the model has low relative errors between 8:00 and 21:00 LT. The estimated O3 maps depict a consistent 24-h variation pattern, characterized by high and most fluctuating concentrations during the daytime, reaching a peak around 16:00 LT, which is primarily due to the increased photochemical reactions and the O3 accumulation in the mid-afternoon. In the daytime of summer, high surface ozone concentrations are mainly contributed by June. The elevated levels of O3 are predominantly found in central China, particularly in the Beijing-Tianjin-Hebei region and Inner Mongolia. It can also be seen that although the highest average daytime surface O3 concentration occurs in summer, the highest nighttime concentration is observed in spring, which may be attributed to the frequent occurrence of horizontal transport and vertical mixing of O3. This study holds promise in providing comprehensive round-the-clock surface O3 data across China, thereby enhancing our understanding of diurnal ground-level O3 variations.

Predicting plateau atmospheric ozone concentrations by a machine learning approach: A case study of a typical city on the southwestern plateau of China

Atmospheric ozone (O3) has been placed on the priority control pollutant list in China's 14th Five-Year Plan. Due to their unique meteorological conditions, plateau regions contain high concentrations of atmospheric O3. However, traditional experimental methods for determining O3 concentrations using automatic monitoring stations cannot predict O3 trends. In this study, two machine learning models (a nonlinear auto-regressive model with external inputs (NARX) and a temporal convolution network (TCN)) were developed to predict O3 concentrations in a plateau area in the Kunming region by considering the effects of meteorological parameters, air quality parameters, and volatile organic compounds (VOCs). The plateau O3 prediction accuracy of the machine learning models was found to be much higher than those of numerical models that served as a comparison. The O3 values predicted by the machine learning models closely matched the actual monitoring data. The temporal distribution of plateau O3 displayed a high all-day peak from February to May. A correlation analysis between O3 concentrations and feature parameters demonstrated that humidity is the feature with the highest absolute correlation (−0.72), and was negatively correlated with O3 concentrations during all test periods. VOCs and temperatures were also found to have high positive correlation coefficients with O3 during periods of significant O3 pollution. After negating the effects of meteorological parameters, the predicted O3 concentrations decreased significantly, whereas they increased in the absence of NOx. Although individual VOCs were found to greatly affect the O3 concentration, the total VOC (TVOC) concentration had a relatively small effect. The proposed machine learning model was demonstrated to predict plateau O3 concentrations and distinguish how different features affect O3 variations.

Responses of surface ozone under the tropical cyclone circulations: Case studies from Fujian Province, China

The circulation of tropical cyclones (TCs) exerts a multifaceted influence on the spatial and temporal distribution of surface pollutants. This study investigates the response of surface ozone (O3) concentration to the TCs in Fujian Province from June to December 2022 by analyzing the contributions of atmospheric pollutants, meteorological conditions, and dynamical transports. Empirical orthogonal function (EOF) decomposition methods are used to analyze the spatio-temporal distribution patterns of affected O3, and a Gradient Boosting Regression Trees (GBRT) machine learning model is employed to estimate surface O3 concentration, quantifying the influence of each factor. The results indicate an anomaly increase in O3 concentration during this period, with photochemistry-related meteorological conditions being the primary influencer, accounting for 66.9% of O3 variations, elucidating the interpretability of the GBRT model for attributing changes in O3 concentration. Low relative humidity and high temperature conditions have been identified as pivotal factors influencing the rise in O3 concentrations. The presence of TC undermines this predominant influence, amplifying the role of transport factors and other atmospheric pollutants. In the case studies of TC (Muifa and Nanmadol, 2022), the slow or stagnant TCs triggered persistent downdrafts in its periphery and brought favorable meteorological conditions such as clear sky and warm temperature for photochemistry. TCs also enhances the impact of horizontal and vertical dynamic transport on O3 concentrations. This work provides vital insights into the complex interplay between TCs and surface O3 concentrations, highlighting the need for targeted environmental and air quality management strategies in regions frequently impacted by TCs.

Disentangling the effects of meteorology and emissions from anthropogenic and biogenic sources on the increased surface ozone in Eastern China

China's Clean Air Actions have substantially improved ambient PM2.5 air quality since 2013. However, ozone (O3) pollution in urban areas has worsened in recent years, particularly in the eastern region. The formation of O3 in these high emission areas is highly complex and regulated by numerous factors. Utilizing the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem), this study conducted a comprehensive analysis through nine sensitivity experiments for the years 2013 and 2017, aimed at disentangling the relative contributions of major factors (e.g., meteorological factors, anthropogenic emissions, biogenic emissions, and aerosol feedback mechanisms) to the observed O3 concentration trends in Jiangsu, a developed region of China with increasing trend of O3 level. Our findings indicate a pronounced increase in mean daily maximum 8-h average (MDA8) O3 levels in the economically vibrant southern Jiangsu, contrasted with a decrease in the less developed northern regions. The study identifies anthropogenic emissions change as the primary driver of O3 variations, with significant impacts also attributed to meteorological conditions and aerosol feedback effects, while biogenic emission shifts play a lesser role. In terms of meteorological factors, we discovered that the alteration in meteorological thermal factors (enhanced solar radiation and temperatures) in 2017, compared to 2013, exerted a more pronounced influence on the formation of O3 than the change in thermally driven dynamic factors (boundary layer height and wind speed). Moreover, the study observes a shift in O3 formation sensitivity from VOC-sensitive to transitional or NOX-sensitive regimes, signifying a notable transformation in the regional atmospheric chemistry conducive to O3 generation. Aerosol feedback effects, through complex pathways including photolysis rate alterations and modifications in the vertical O3 distribution, further compound the challenge of mitigating O3 levels. Our research underscores the necessity for adaptive, region-specific strategies to mitigate O3 pollution, providing potential insights for policymakers to formulate effective control measures.

Detecting atmospheric oxidation in the PM2.5 and ozone multilayer complex network

Abstract Reducing the levels of Fine particulate matter (PM2.5) and ozone (O3) is essential for further improving air quality in China. The intricate and non-linear interactions between PM2.5 and O3 on a national scale over long-term records are not well understood. Here, we proposed a novel multi-layer network approach to bridge the gap. Our findings reveal that the variability of O3 precedes that of PM2.5 by one day. The degree, weighted degree, and edge distance follow a power-law decay distribution, suggesting that their relationship is not a random process. O3 concentration in the Yangtze River Delta (YRD) region and eastern Shandong Province significantly impacts the PM2.5 levels in surrounding areas. Conversely, PM2.5 concentrations in Shandong Province, Henan Province, YRD and Pearl River Delta (PRD) have a strong influence on O3 levels. Moreover, we quantified the seasonality of the interactions and elucidated the underlying reasons. The results revealed the interactions between PM2.5 and O3 are intricately tied to atmospheric oxidation processes. More specifically, in summer, the atmospheric oxidation has a strong impact on the interactions in key regions, such as the Beijing–Tianjin–Hebei,YRD region and Fenwei Plain. However, the PRD region experiences a more pronounced effect from atmospheric oxidation on this relationship in winter. These findings demonstrate that it is crucial to effectively regulate atmospheric oxidation to mitigate PM2.5 and O3. Our results also serve as a valuable methodological framework for understanding the characteristics of pollutants.

Effect of Meteorological Elements and Air Pollutants on Ozone in Yinchuan City Park

To examine the underlying determinants of ozone （O3） in Yinchuan's urban park during varying seasons and to ascertain the role played by meteorological events and air contaminants in influencing O3 concentrations at high altitudes, data on O3, meteorological factors, and air pollutants were collected through prolonged positional observations carried out at the Ningxia Yinchuan National Urban Ecosystem Research Station. Pearson correlation analysis and a structural equation model were utilized to investigate the spatio-temporal distribution patterns, trends, and the primary factors influencing O3. The findings demonstrated a notable seasonal variability in O3 levels in Yinchuan's urban park, displaying an "unimodal type" with the O3 concentration peaking in summer （131.18 μg·m-3） and bottoming out in winter （71.45 μg·m-3）. Among the meteorological factors, the highest impact on O3 was attributed to temperature and wind speed （temperature mainly through direct effects and wind speed mainly through indirect effects）. Conversely, air pollutants such as NOx and SO2 greatly affected O3 primarily through direct effects. Wind speed was identified as the primary influencing factor on O3 during spring and summer, potentially contributing 29% and 24.7%, respectively. Conversely, NO2 was implicated as the primary factor during autumn and winter, with an estimated contribution of 26.6% and 29.7%, respectively. Thus, a structural equation model can efficiently reveal the primary determinants behind O3 variations throughout various seasons, which could furnish a scientifically rigorous foundation and technical aid for mitigating and managing O3 levels in high-altitude regions.

Fine particulate matter and ozone variability with regional and local meteorology in Beijing, China

Fine particulate matter (PM2.5) and surface ozone air pollution have severe health consequences. Since China implemented the nationwide Air Pollution Prevention and Control Action Plan (APPCAP) in 2013, annual average PM2.5 concentrations have decreased while O3 concentration have increased in Beijing. It is unclear, however, to the extent that short-term meteorological variability has influenced these trends. To separate the influence of meteorology from long-term emissions-induced changes, we quantify the portion of the long-term PM2.5 and O3 concentration signals associated with short-term meteorological variability. Building off recent literature highlighting the regional nature of pollutant variability, we incorporate both locally observed meteorology and average regional reanalysis. We isolated sub-seasonal variability using the Kolmogorov-Zurbenko filter. Next, we trained and compared the utility of three statistical models of varying complexity (a linear model, a general additive model with splines, and a random forest) in their ability to predict out-of-sample daily concentrations. The random forest model yields the best predictive capability in holdout tests and predicts changing meteorological contributions to PM2.5 and ozone concurrent with changing concentrations across the study period. Results show an overall decrease in meteorology induced PM2.5 concentration variability at daily scales since 2013, but variability from meteorology has increased relative to mean PM2.5 concentrations. In contrast, O3 shows the opposite trend, with increasing meteorology-induced variability (meteorology-induced variability normalized by mean observed O3 has decreased). Our results show the importance of including regional meteorology in explaining local PM2.5 and O3 variability and quantify links between long-term policy implementation and short-term meteorological contributions to pollutant concentrations.

Synoptic controls on warm-season O3 pollution in eastern China: A focus on O3-NOx-VOC chemistry

The design of emission abatement measures to effectively reduce ozone (O3) pollution is highly complex due to non-linear chemistry, multi-source precursor emissions, and regional-scale transport. All these processes also depend on the synoptic circulation conditions. This study classified large-scale circulations to explore the synoptic controls on surface O3 pollution over eastern China (EC) during the warm seasons (May to September) from 2013 to 2022. Four prevailing circulation patterns (CPs) were identified, distinguishable by distinct differences in surface O3 anomaly distribution over the EC region. Regional meteorological variables, satellite-based precursors (NO2 and CH2O), and CH2O/NO2 ratio-based O3 formation sensitivity (OFS) were projected onto each CP to explore the underlying physiochemical mechanism of synoptic midualtion to surface O3 pollution. The results indicated that circulation-driven regional transport governed the spatial variability of surface O3 anomaly distribution on a synoptic timescale. Additionally, circulation-driven temperature changes caused unsynchronized changes in NO2 and CH2O across different CPs, leading to circulation-dependent OFS distribution. Geographical O3 anomaly changes generally followed the O3-VOC-NOx chemical principle in most synoptic circulation situations, thereby providing a framework for formulating spatiotemporal sensitivity-oriented mitigation strategies for forthcoming O3 pollution episodes with the assistance of synoptic circulation forecasts.

Long-Term Variability of Surface Ozone and Its Associations with NOx and Air Temperature Changes from Air Quality Monitoring at Belsk, Poland, 1995–2023

Surface ozone (O3) and nitrogen oxides (NOx = NO + NO2) measured at the rural station in Belsk (51.83° N, 20.79° E), Poland, over the period of 1995–2023, were examined for long-term variability of O3 and its relationship to changes in the air temperature and NOx. Negative and positive trends were found for the 95th and 5th percentile, respectively, in the O3 data. A weak positive correlation (statistically significant) of 0.33 was calculated between O3 and the temperature averaged from sunrise to sunset during the photoactive part of the year (April–September). Recently, O3 maxima have become less sensitive to temperature changes, reducing the incidence of photochemical smog. The ozone–climate penalty factor decreased from 4.4 µg/m3/°C in the 1995–2004 period to 3.9 µg/m3/°C in the 2015–2023 period. The relationship between Ox (O3 + NO2) and NOx concentrations averaged from sunrise to sunset determined the local and regional contribution to Ox variability. The seasonal local and regional contributions remained unchanged in the period of 1995–2023, stabilizing the average O3 level at Belsk. “NOx-limited” and “VOC-limited” photochemical regimes prevailed in the summer and autumn, respectively. For many winter and spring seasons between 1995 and 2023, the type of photochemical regime could not be accurately determined, making it difficult to build an effective O3 mitigation policy.

Estimation of Regional Background Ozone in Henan Province from 2019 to 2021

Clarifying the regional transmission and local generation contributions of ozone （O3） is important for controlling O3 pollution. To quantify the regional background and spatial-temporal variations of O3, a comprehensive study was conducted using multiple methods including principal component analysis （PCA） and TCEQ, with Henan Province as a case study. Based on monitoring data from 59 national sites in Henan Province during 2019-2021, four methods were employed to estimate the regional background of O3. Method 1 was the traditional method, performing O3 univariate-multisite PCA analysis. Method 2 was a multivariate-single-site PCA analysis considering nitrogen dioxide and meteorological conditions as constraints. Method 3 combined PCA and multiple linear regression （MLR） to determine regional background contributions, drawing on the idea of source apportionment. Method 4 was the TCEQ method that used the lowest measured O3-8h concentration as the regional background. The estimation results showed that Methods 1 and 2 were basically equal, and Methods 3 and 4 were approximately 37-60 μg·m-3 lower than Method 1. From 2019 to 2021, the changes in regional background ρ（O3-8h） estimated by Methods 1-4 were 1.6, -13.4, 5.9, and -3.5 μg·m-3, respectively. The average estimations derived from multiple methods showed that the regional background ρ（O3-8h） in Henan Province from 2019 to 2021 concentrations were 82.0, 79.0, and 79.7 μg·m-3, accounting for 75.9%, 76.4%, and 78.7% of the total regional O3-8h, respectively. The regional background O3-8h estimated by the four methods showed obvious seasonal changes, characterized by summer > spring > fall > winter.

Spatiotemporal Distribution Characteristics of Ground-level-ozone and Its Relationship with Meteorological Conditions in a Representative City in the Bohai Rim from 2017 to 2022

In recent years, ground-level-ozone（O3） pollution in urban areas in the Bohai Rim has attracted wide attention. Based on the analysis of the spatiotemporal distribution characteristics of O3 concentration in Dongying, a representative city in the Bohai Rim from 2017 to 2022, the effects of meteorological factors and sea-land breeze circulation on O3 concentration were evaluated. The results showed that： ① From 2017 to 2022, the annual assessment value of O3 concentration in Dongying showed a fluctuating upward trend, and the pollution days with O3 as the primary pollutant increased. O3 pollution mainly occurred in spring, summer, and autumn, with the most severe O3 pollution episodes typically occurring in May and June, and the duration of O3 pollution season tended to be longer. The monthly variation in the daily maximum 8-h average ozone （MDA8 O3） presented a bimodal distribution, with significant increases in the 5th and 25th percentiles, and the spatial distribution was "high in the north and south, low in the middle." In addition, the nocturnal O3 concentration in recent years in Dongying also showed a significant increase trend. ② Meteorological factors greatly influenced O3 concentration in Dongying. When the temperature was greater than 30℃, the relative humidity was less than 50%, and the wind direction was south-southwest or east-northeast, a high O3 value was more likely to occur. Meteorological factors contributed 30% of the MDA8 O3 variation in Dongying during the study period. In the case of moderate and severe O3 pollution, the contribution of meteorological factors to the change in MDA8 O3 could be as high as 40%. ③ To some extent, sea-land breeze contributed to the occurrence of MDA8 O3 exceeding the secondary standard limit value of the National Ambient Air Quality Standard. In the afternoon, the hourly concentration of O3 during the sea-land breeze days was approximately 20 μg·m-3 higher than that during the non-sea-land breeze days. On the days of moderate and severe O3 pollution, the O3 concentration during the sea-land breeze days from 10：00 to 16：00 was higher than that during non-sea-land breeze days, and the O3 concentration was also at a high level from 20：00 to 23：00 on sea-land breeze days. In the O3 pollution season, the sea-land breeze could significantly affect the O3 level in coastal cities, which could bring significant challenges for O3 pollution prevention and control in this region. In the future, cities in the Bohai Rim need to further strengthen regional joint prevention and control of O3 pollution and increase emission reduction efforts of nitrogen oxides and volatile organic compounds. This strategy could effectively lower pollutant concentrations within the land breeze air mass, consequently reducing the impact of the sea breeze air mass on air quality in cities in the Bohai Rim.

Understanding the variability of ground-level ozone and fine particulate matter over the Tibetan plateau with data-driven approach

The Tibetan Plateau, known as the “Third Pole”, is susceptible to ground-level ozone (O3) and fine particulate matter (PM2.5) pollution due to its unique high-altitude environment. This study constructed random forest regression models using multi-source data from ground measurements and meteorological satellites to predict variations in ground-level O3 and PM2.5 concentrations and their influencing factors across seven major cities in the Tibetan Plateau over two-year periods. The models successfully reproduced O3 and PM2.5 levels with satisfactory R-squared values of 0.71 and 0.73, respectively. Results reveal combustion-related carbon monoxide (CO) and nitrogen dioxide (NO2) as the most substantial influences on O3 and PM2.5 concentrations. Solar radiation, geographical factors, and meteorological variables also played crucial roles in driving pollutant variations. Conversely, transport-related and human activity factors exhibited relatively lower significance. High O3 and PM2.5 pollution occurred during pre-monsoon and post-monsoon/winter seasons, driven by solar radiation and emissions, respectively. While CO consistently contributed across cities and seasons, key influencing factors varied locally. This study unveils the key driving forces governing air pollutant variations across the Tibetan Plateau, shedding light on complex atmospheric processes in this unique high-altitude region.

Deciphering the seasonal dynamics of multifaceted aerosol-ozone interplay: Implications for air quality management in Eastern China

We employed an enhanced WRF-Chem to investigate the discrete mechanisms of aerosol-radiation-feedback (ARF), extinction-photochemistry (AEP), and heterogeneous-reactions (AHR) across different seasons in eastern China, aiming to assess the synergistic effects arising from the simultaneous operation of multiple processes on O3 and PM2.5. Our findings demonstrated that ARF fostered the accumulation of pollutants and moisture, initiating two distinct feedback mechanisms concerning O3. The elevation in the NO/NO2 ratio amplified O3 consumption. Increased near-surface moisture diminished upper-level cloud formation, thereby enhancing photolysis rates and O3 photochemical production. The pronounced impact of heightened NO/NO2 on O3 led to a decrease of 0.1–2.7 ppb. When decoupled from ARF, AEP led to a more significant reduction in photolysis rates, resulting in declines in both O3 and PM2.5, except for an anomalous increase observed in summer, with O3 increasing by 1.6 ppb and PM2.5 by 2.5 μg m−3. The heterogeneous absorption of hydroxides in spring, autumn, and winter predominantly governed the AHR-induced variation of O3, leading to a decrease in O3 by 0.7–1 ppb. Conversely, O3 variations in summer were primarily dictated by O3-sensitive chemistry, with heterogeneous absorption of NOy catalyzing a decrease of 2.4 ppb in O3. Furthermore, AHR accentuated PM2.5 by facilitating the formation of fine sulfates and ammonium while impeding nitrate formation. In summer, the collective impact of ARF, AEP, and AHR (ALL) led to a substantial reduction of 6.2 ppb in O3, alleviating the secondary oxidation of PM2.5 and leading to a decrease of 0.3 μg m−3 in PM2.5. Conversely, albeit aerosol substantially depleted O3 by 0.4–4 ppb through their interactions except for summer, aerosol feedback on PM2.5 was more pronounced, resulting in a significant increase of 1.7–6.1 μg m−3 in PM2.5. Our study underscored the seasonal disparities in the ramifications of multifaceted aerosol-ozone interplay on air quality.

Spatiotemporal variability of surface ozone and associated meteorological conditions over the Arabian Peninsula

This study investigates the spatiotemporal variability of surface ozone (O3) over the Arabian Peninsula (AP) between 2005 and 2019, focusing on the Arabian Gulf (AG). The analysis explores the relationship between surface O3 data from the Copernicus Atmosphere Monitoring Service (CAMS) with boundary layer height (BLH), 2 m temperature (T2M), downward ultraviolet radiation at the surface (UVB), and 10 m wind speed (WS) and direction from the fifth generation European Centre for Medium-Range Weather Forecasts (ECMWF) atmospheric reanalysis (ERA5). Also, the study considers Carbon Monoxide (CO) and Nitrogen Oxides (NOx) surface emissions from the Tropospheric Chemical Reanalysis version 2 (TCR-2). Furthermore, it investigates the impact of El Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) on surface O3 variations on a seasonal scale. Surface O3 observations from 15 ground-based stations across the AP were used to evaluate CAMS-O3, showing a good agreement between CAMS and the observations. The analysis of mean diurnal variations of CAMS-O3 and ERA5 reveals that surface O3 is highest over the eastern parts of the AP, mainly the AG, peaking during summer, followed by spring, fall, and winter. This seasonal cycle is also observed, to a large degree, in BLH, T2M, UVB, and WS. The results also reveal insignificant correlation between surface O3 and ENSO, but stronger correlation with IOD, especially over the AG during summer and fall. The analysis indicates that elevated T2M and UVB during daytime and elevated BLH during nighttime are significant contributors to increased levels of O3 over the AG.

Response of ozone to meteorology and atmospheric oxidation capacity in the Yangtze river Delta from 2017 to 2020

China implemented a stringent clean air initiative to improve air quality in 2013. By 2017, fine particulate matter (PM2.5) levels in the Yangtze River Delta (YRD) region dropped significantly, but ozone (O3) pollution surged, which aroused concerns about its adverse impact on crops, climate and human health. Due to the complex influences of atmospheric processes, the variation of O3 is highly nonlinear, making the control of O3 pollution highly challenging. It is urgent to deepen the understanding of the role of meteorological factors and atmospheric oxidation capacity (AOC) during O3 episodes. To provide references for O3 pollution control, the study used the Weather Research and Forecasting model (WRF) and the Community Multi-scale Air Quality model (CMAQ) simulations in the YRD from 2017 to 2020 to analyze the causes of severe O3 pollution. Observations revealed a slight decline in heavily O3 polluted days in the YRD region and the simulation results showed that O3 pollution was more prevalent at temperatures above 25 °C and relative humidity below 80%. The increase in volatile organic compounds (VOCs), hydroxyl radical (OH) and nitrate radical (NO3) was also more conducive to the formation of O3 pollution. For areas that are primarily VOC-limited areas, such as Shanghai, a stricter policy on VOC control is needed to reduce O3 pollution more effectively.

Ozone pollution aggravated by mountain-valley breeze over the western Sichuan Basin, Southwest China

The impact of thermally driven mountain-valley breezes (MVB) on the atmospheric environment remains poorly understood, especially in ozone (O3)-polluted regions with complex underlying topography. To address this knowledge gap, we focused on the western Sichuan Basin (SCB), situated immediately east of the Tibetan Plateau (TP), which is considered susceptible to MVB coupled with severe O3 pollution in southwest China. We revealed the MVB driving diurnal O3 variations and meteorological mechanisms using surface observations and ERA5 reanalysis data. Local MVB days accounted for up to 47% of cases in the summers of 2015–2022. Driven by the MVB, the near-surface O3 concentrations increased by 8.8%, with 12.7% and 50.0% deterioration in the O3 light and moderate exceedance rates, respectively, on the western SCB edge. The daytime upslope valley breeze with 20% higher wind speed drove the westward transport of rich O3 and precursors from the upwind-polluted inner SCB towards its western edge, and the O3 photochemical production, followed by intensifying solar radiation and air temperature, gave rise to 14.8% of surface O3 concentrations over the western SCB edge. The nighttime downward mountain breeze with a 20% increase in wind speed could transport the rich O3 in the mountainous area to the basin edge, causing O3 levels to increase by 2.8%. In summary, we quantitatively assessed the impacts of MVB on changes in O3 concentrations and air quality along with its meteorological mechanisms, facilitating a comprehensive understanding of meteorological drivers in the atmospheric environment.

Elucidating the Effects of COVID-19 Lockdowns in the UK on the O3-NOx-VOC Relationship

The unprecedented reductions in anthropogenic emissions over the COVID-19 lockdowns were utilised to investigate the response of ozone (O3) concentrations to changes in its precursors across various UK sites. Ozone, volatile organic compounds (VOCs) and NOx (NO+NO2) data were obtained for a 3-year period encompassing the pandemic period (January 2019–December 2021), as well as a pre-pandemic year (2017), to better understand the contribution of precursor emissions to O3 fluctuations. Compared with pre-lockdown levels, NO and NO2 declined by up to 63% and 42%, respectively, over the lockdown periods, with the most significant changes in pollutant concentrations recorded across the urban traffic sites. O3 levels correspondingly increased by up to 30%, consistent with decreases in the [NO]/[NO2] ratio for O3 concentration response. Analysis of the response of O3 concentrations to the NOx reductions suggested that urban traffic, suburban background and suburban industrial sites operate under VOC-limited regimes, while urban background, urban industrial and rural background sites are NOx-limited. This was in agreement with the [VOC]/[NOx] ratios determined for the London Marylebone Road (LMR; urban traffic) site and the Chilbolton Observatory (CO; rural background) site, which produced values below and above 8, respectively. Conversely, [VOC]/[NOx] ratios for the London Eltham (LE; suburban background) site indicated NOx-sensitivity, which may suggest the [VOC]/[NOx] ratio for O3 concentration response may have had a slight NOx-sensitive bias. Furthermore, O3 concentration response with [NO]/[NO2] and [VOC]/[NOx] were also investigated to determine their relevance and accuracy in identifying O3-NOx-VOC relationships across UK sites. While the results obtained via utilisation of these metrics would suggest a shift in photochemical regime, it is likely that variation in O3 during this period was primarily driven by shifts in oxidant (OX; NO2 + O3) equilibrium as a result of decreasing NO2, with increased O3 transported from Europe likely having some influence.

Observational analysis of surface ozone variability in China from 2015 to 2020: Insights from consecutive ENSO episodes

Utilizing daily surface ozone (O3) concentration data (MDA8-O3) from nearly 1500 monitoring stations across mainland China, complemented by gridded atmospheric reanalysis data, this study conducts a comprehensive analysis of O3 concentration, anomalies, and oscillations. Employing regression and composite analyses, we investigate the potential linkage between O3 variations and the phase and strength of El Niño-Southern Oscillation (ENSO) across diverse regions and seasons in China. Noteworthy findings include the identification of regions exhibiting peak O3 concentrations in autumn or spring, deviating from the typical seasonal cycle, as well as regions exhibiting varying strengths of seasonal and semi-annual O3 oscillations. Moreover, the study unveils the spatiotemporal patterns of synoptic and intra-seasonal O3 oscillations. The analyses reveal a prevailing inverse association between O3 anomalies and ENSO in most Chinese regions except for the southern and southeastern coastal areas. The potential impacts of ENSO on O3 are elucidated by anomalous atmospheric conditions linked to ENSO, the nature of which strongly depends on the region and season. In northern China, anomalous temperature and solar radiation related to ENSO exert a more pronounced influence on O3 anomalies. On the other hand, in southern China, anomalies in wind speed/direction and precipitation associated with anomalous atmospheric circulations play a more predominant role. These findings contribute valuable insights to the nuanced understanding of O3 variability, paving the way for the development of sophisticated O3 forecasting approaches tailored to different regions and seasons across China.

A better representation of VOC chemistry in WRF-Chem and its impact on ozone over Los Angeles.

The declining trend in vehicle emissions has underscored the growing significance of Volatile Organic Compound (VOC) emissions from Volatile Chemical Products (VCP). However, accurately representing VOC chemistry in simplified chemical mechanisms remains challenging due to its chemical complexity including speciation and reactivity. Previous studies have predominantly focused on VOCs from fossil fuel sources, leading to an underrepresentation of VOC chemistry from VCP sources. We developed an integrated chemical mechanism, RACM2B-VCP, that is compatible with WRF-Chem and is aimed to enhance the representation of VOC chemistry, particularly from VCP sources, within the present urban environment. Evaluation against the Air Quality System (AQS) network data demonstrates that our model configured with RACM2B-VCP reproduces both the magnitude and spatial variability of O3 as well as PM2.5 in Los Angeles. Furthermore, evaluation against comprehensive measurements of O3 and PM2.5 precursors from the Reevaluating the Chemistry of Air Pollutants in California (RECAP-CA) airborne campaign and the Southwest Urban NO x and VOC Experiment (SUNVEx) ground site and mobile laboratory campaign, confirm the model's accuracy in representing NOx and many VOCs and highlight remaining biases. Although there exists an underprediction in the total VOC reactivity of observed VOC species, our model with RACM2B-VCP exhibits good agreement for VOC markers emitted from different sectors, including biogenic, fossil fuel, and VCP sources. Through sensitivity analyses, we probe the contributions of VCP and fossil fuel emissions to total VOC reactivity and O3. Our results reveal that 52% of the VOC reactivity and 35% of the local enhancement of MDA8 O3 arise from anthropogenic VOC emissions in Los Angeles. Significantly, over 50% of this anthropogenic fraction of either VOC reactivity or O3 is attributed to VCP emissions. The RACM2B-VCP mechanism created, described, and evaluated in this work is ideally suited for accurately representing ozone for the right reasons in the present urban environment where mobile, biogenic, and VCP VOCs are all important contributors to ozone formation.