Near-surface O3 Research Articles

Source attribution of near-surface ozone trends in the United States during 1995–2019

Abstract. Emissions of ozone (O3) precursors in the United States have decreased in recent decades, and near-surface O3 concentrations showed a significant decrease in summer but an increase in winter. In this study, an O3 source tagging technique is utilized in a chemistry–climate model to investigate the source contributions to O3 mixing ratios in the US from various emitting sectors and regions of nitrogen oxides (NOx) and reactive carbon species during 1995–2019. We show that domestic emission reductions from energy and surface transportation are primarily responsible for the decrease in summertime O3 during 1995–2019. However, in winter, the emission control also weakens the NOx titration process, resulting in considerable increases in O3 levels from natural sources. Additionally, increases in aviation and shipping emissions and transpacific transport of O3 from Asia largely contribute to the winter O3 increase. We also found that changes in large-scale circulation favoring O3 transport from the upper atmosphere and foreign transport from Asia also explain 15 % of the increase in the US near-surface O3 levels in winter.

Rapid increase in tropospheric ozone over Southeast Asia attributed to changes in precursor emission source regions and sectors

Observations indicate that tropospheric ozone (O3) concentrations over Southeast Asia have been increasing rapidly since the 1990s. Here, we quantify source contributions from geographical regions and emission sectors of the two distinct types of O3 precursors, i.e., nitrogen oxides (NOx) and volatile organic compounds (VOCs), to the increase in tropospheric O3 in Southeast Asia during 1990–2019 using an O3 source tagging technique implemented in a global chemistry-climate model. The results show that although local anthropogenic emission of NOx in Southeast Asia only contributes 18% of the annual averaged near-surface O3 concentration, the increase in local NOx emission dominates the increasing trend of O3 concentration in Southeast Asia, accounting for 107% of the regional averaged trend of 1.07 ppb decade−1. Increases in NOx emissions from East Asia and South Asia explain 29% of the increasing trend, but 9% is offset by the emission reduction in North America. The vertical O3 trends in the troposphere contributed by individual source regions are consistent with those near the surface. Ground transportation is responsible for 79% of the rapid O3 increase, followed by 39% contribution from international shipping. Because an increase in anthropogenic NOx emissions enhances the O3 production efficiency by VOCs, the increase in O3 concentrations in Southeast Asia is thereby largely contributed by methane and biogenic VOCs.

Global reanalysis products cannot reproduce seasonal and diurnal cycles of tropospheric ozone in the Congo Basin

Tropospheric ozone (O3) is a secondary pollutant and a greenhouse gas with a positive radiative forcing. Many studies have documented its negative impacts on plant growth and human health. Historically, studies have focused on determining levels of exposure in mid- and high-latitude regions. In the tropics, high O3 concentrations are expected due to large concurrent and future precursor emissions. In Africa, seasonal biomass burning (from both natural and anthropogenic fires) during the dry season plays a crucial role in O3 precursor production. However, O3 observational studies in tropical Africa are currently missing. To fill this major knowledge gap, we established in November 2019 a continuous monitoring of near-surface O3 in the Congo Basin at the Yangambi research centre in the Democratic Republic of the Congo. Using this unique dataset in the heart of the second-largest tropical forest in the world, we assessed the ability of current remote sensing products to capture the magnitude and temporal dynamics of in situ tropospheric O3 concentrations, especially O3 concentration variation between dry and wet seasons until March of 2022. We compared near-surface atmospheric O3 measurements collected in Yangambi and four different reanalysis products: European Centre for Medium-Range Weather Forecasts Reanalysis (ECMWF) v5 (ERA5), Copernicus Atmospheric Monitoring Service reanalysis (CAMSRA), Modern-Era Retrospective Analysis for Research and Applications version 2 (MERRA-2) and Japanese Reanalysis (JRA-55). The results show that reanalysis products overestimated the magnitude of near-surface O3 across the region with a mean bias of 27.3 ppbv, 19.9 ppbv, 10.8 ppbv and 1.0 ppbv for ERA5, CAMSRA, MERRA-2 and JRA-55, respectively. ERA5 and CAMSRA reanalysis were the only products able to capture, to some extent, the observed annual variation, showing higher O3 concentrations during dry season months, despite the inability to reproduce the daily cycle of near-surface O3.

Summertime ozone pollution in China affected by stratospheric quasi-biennial oscillation

Abstract. In recent years, the near-surface ozone (O3) level has been rising fast in China, with increasing damage to human health and ecosystems. In this study, the impact of stratospheric quasi-biennial oscillation (QBO) on interannual variations in summertime tropospheric O3 over China is investigated based on GEOS-Chem model simulations and satellite retrievals. QBO has a significant positive correlation with near-surface O3 concentrations over central China (92.5–112.5∘ E, 26–38∘ N) when the sea surface temperature (SST) over the eastern tropical Pacific is warmer than normal, with a correlation coefficient of 0.53, but QBO has no significant effect on O3 under the cold SST anomaly. Compared to the easterly phase of QBO, the near-surface O3 concentrations have an increase of up to 3 ppb (5 % relative to the average) over central China during its westerly phase under the warm SST anomaly. O3 also increases above the surface and up to the upper troposphere, with a maximum increase of 2–3 ppb (3 %–5 %) in 850–500 hPa over central China when comparing westerly phase to easterly phase. Process-based analysis and sensitivity simulations suggest that the O3 increase over central China is mainly attributed to the anomalous downward transport of O3 during the westerly phase of QBO when a warm SST anomaly occurs in the eastern tropical Pacific, while the local chemical reactions and horizontal transport processes partly offset the O3 increase. This work suggests a potentially important role of QBO and the related vertical transport process in affecting near-surface O3 air quality, with an indication for O3 pollution prediction and prevention.

Climate-driven deterioration of future ozone pollution in Asia predicted by machine learning with multi-source data

Abstract. Ozone (O3) is a secondary pollutant in the atmosphere formed by photochemical reactions that endangers human health and ecosystems. O3 has aggravated in Asia in recent decades and will vary in the future. In this study, to quantify the impacts of future climate change on O3 pollution, near-surface O3 concentrations over Asia in 2020–2100 are projected using a machine learning (ML) method along with multi-source data. The ML model is trained with combined O3 data from a global atmospheric chemical transport model and real-time observations. The ML model is then used to estimate future O3 with meteorological fields from multi-model simulations under various climate scenarios. The near-surface O3 concentrations are projected to increase by 5 %–20 % over South China, Southeast Asia, and South India and less than 10 % over North China and the Gangetic Plains under the high-forcing scenarios in the last decade of 21st century, compared to the first decade of 2020–2100. The O3 increases are primarily owing to the favorable meteorological conditions for O3 photochemical formation in most Asian regions. We also find that the summertime O3 pollution over eastern China will expand from North China to South China and extend into the cold season in a warmer future. Our results demonstrate the important role of a climate change penalty on Asian O3 in the future, which provides implications for environmental and climate strategies of adaptation and mitigation.

Stratospheric intrusion may aggravate widespread ozone pollution through both vertical and horizontal advections in eastern China during summer

Stratospheric intrusion (SI) is an important source of tropospheric ozone (O3). Here, we used the online coupled Weather Research and Forecasting-Chemistry (WRF-Chem) model to simulate a typical SI event that occurred over eastern China on 15–19 July 2016 and investigate the impacts of SI on near-surface O3 pollution. The results show that the large-scale circulation of SI was characterized by a deep trough over central China and South Asia high and Western Pacific Subtropical high located to the east and west of the deep trough, respectively. With the evolution of the deep trough, the strong downdrafts behind the trough lead to O3-rich air injected into the lower troposphere across eastern China. By using a tracer tagging method in WRF-Chem, we quantified the SI contributed up to 6.5 ppb to the surface O3 concentration. According to the integrated process rate analyses, which were employed to quantify the contribution of different physical/chemical processes to O3, the advection process dominated variations in troposphere O3 with positive contribution ranging from 0.1 to 13.8 ppb h−1. As altitude decreases, the contribution of advection diminishes as the intensity of the SI gradually weakens. Although the vertical advection contributed limited O3 that directly reached the ground, we revealed that the SI has significant impact on near-surface O3 over a large territory of eastern China through regional transport by horizontal advection process. Below 691 m, the positive contribution of horizontal advection to O3 ranges from 1.6 to 13.4 ppb h−1. This study highlights the natural effect of SI on summertime O3 pollution in eastern China and will help the development of a future O3 pollution alert system.

Estimation of near-surface ozone concentration and analysis of main weather situation in China based on machine learning model and Himawari-8 TOAR data

Ozone (O3) is an important greenhouse gas in the atmosphere. Stratospheric ozone protects human beings, but high near-surface ozone concentrations threaten environment and human health. Owing to the uneven distribution of ground-monitoring stations and the low time resolution of polar orbiting satellites, it is difficult to accurately evaluate the refinement and synergistic pollution of near-surface ozone in China. Besides, atmospheric circulation patterns also affect ozone concentrations greatly. In this study, a new generation of geostationary satellite is used to estimate the hourly near-surface ozone concentration with a spatial resolution of 0.05°. First, the Pearson correlation coefficient and maximum information coefficient were used to study the correlation between the top of atmospheric radiation (TOAR) of Himawari-8 satellite and O3 concentration; seven TOAR channels were selected. Second, based on an interpretable deep learning model, the hourly ozone concentration in China from September 2015 to August 2021 was obtained using the TOAR-O3 model. Finally, the self-organizing map method was used to determine six major summer weather circulation patterns in China. The results showed that (1) the near-surface O3 concentration can be accurately estimated; the R2 (RMSE: μg/m3) values of the daily, monthly, and annual tenfold cross validation results were 0.91 (12.74), 0.97 (5.64), and 0.98 (1.75), respectively. The feature importance of the model showed that the temperature, TOAR, and boundary layer height contributed 38 %, 22 %, and 13 %, respectively. (2) The O3 concentration showed obvious spatiotemporal difference and gradually increased from 10:00 to 15:00 (Beijing time) every day. In most areas of China, O3 concentration had increased significantly. (3) The O3 concentration in northern China was the highest under the circulation pattern of the Meiyu front over the Yangtze River Delta, while in southern China, it was the highest under the circulation pattern of the northeast cold vortex controlling most of China.

Changes in the height of the pollution boundary layer and their meteorological effects on the distribution of surface ozone concentrations

Focusing on the key air pollution regions in China by using hourly automatic weather data, ground-based and high-altitude meteorological sounding data, and near-surface O3 monitoring data, here, we try to quantify the relationship between boundary layer meteorological condition and near-surface O3 concentrations. The key meteorological element includes changes in solar zenith angle, cloud height, atmospheric condensation rate, and the associated change in the boundary layer height. We also try to better understand the mechanisms by which meteorological conditions affect near-surface O3 concentrations, and it is found that the exponential increase in near-surface O3 concentrations after sunrise (called the O3 concentration entrainment, EZ) is meaningfully associated with exceeding the threshold of a water vapor condensation rate (fc) that is often closely linked to a significant rise in the pollution boundary layer and that this proves to be diagnostically important for understanding the O3 EZ. Diurnal variations in solar zenith angle and boundary layer height are key meteorological factors influencing the large increase in near-surface O3 concentration entrainment.

Establishment and Application of Foshan Ozone Concentration Forecast Equation

The formation and changes of ozone (O3), a secondary pollutant in the atmosphere, are complex, and ozone forecasting has become one of the current problems in air pollution prevention and control. In this study, the relationships between the near-surface O3 concentration and meteorological elements (high- and low-level) in Foshan from 2014 to 2017 were analyzed, and the concentration forecasting equation was established, tested, and applied. The results showed that the near-surface O3 changed closely related to high- and low-level meteorological elements. Meteorological elements such as temperature and sunshine hours were significantly positively correlated with O3 concentration, whereas relative humidity, total (low) cloud cover, and wind speed were negatively correlated with O3. Heavy O3 pollution often occurred with meteorological conditions of low wind speed, sunny days and few clouds, low relative humidity, longer sunshine time, and higher temperature. The definitions of high-concentration O3 potential index (HOPI) and wind direction index (WDI) in the Foshan area could better characterize the meteorological conditions of O3 pollution. Considering 13 meteorological elements, such as HOPI and WDI at different heights, the O3 concentration forecasting equation in the Foshan area was established using multi-indicator stacking and multiple stepwise regression methods. Using the 2018 data, it was found that the correlation coefficient R between the simulated values and the measured values reached 0.82, and the forecast equation had a good fitting effect and predictability.

Hourly Seamless Surface O3 Estimates by Integrating the Chemical Transport and Machine Learning Models in the Beijing-Tianjin-Hebei Region

Surface ozone (O3) is an important atmospheric trace gas, posing an enormous threat to ecological security and human health. Currently, the core objective of air pollution control in China is to realize the joint treatment of fine particulate matter (PM2.5) and O3. However, high-accuracy near-surface O3 maps remain lacking. Therefore, we established a new model to determine the full-coverage hourly O3 concentration with the WRF-Chem and random forest (RF) models combined with anthropogenic emission data and meteorological datasets. Based on this method, choosing the Beijing-Tianjin-Hebei (BTH) region in 2018 as an example, full-coverage hourly O3 maps were generated at a horizontal resolution of 9 km. The performance evaluation results indicated that the new model is reliable with a sample (station)-based 10-fold cross-validation (10-CV) R2 value of 0.94 (0.90) and root mean square error (RMSE) of 14.58 (19.18) µg m−3. In addition, the estimated O3 concentration is accurately determined at varying temporal scales with sample-based 10-CV R2 values of 0.96, 0.98 and 0.98 at the daily, monthly, and seasonal scales, respectively, which is highly superior to traditional derivation algorithms and other techniques in previous studies. An initial increase and subsequent decrease, which constitute the diurnal variation in the O3 concentration associated with temperature and solar radiation variations, were captured. The highest concentration reached approximately 112.73 ± 9.65 μg m−3 at 15:00 local time (1500 LT) in the BTH region. Summertime O3 posed a high pollution risk across the whole BTH region, especially in southern cities, and the pollution duration accounted for more than 50% of the summer season. Additionally, 43 and two days exhibited light and moderate O3 pollution, respectively, across the BTH region in 2018. Overall, the new method can be beneficial for near-surface O3 estimation with a high spatiotemporal resolution, which can be valuable for research in related fields.

Estimation of the Near-Surface Ozone Concentration with Full Spatiotemporal Coverage across the Beijing-Tianjin-Hebei Region Based on Extreme Gradient Boosting Combined with a WRF-Chem Model

With the intensification of global warming and economic development in China, the near-surface ozone (O3) concentration has been increasing recently, especially in the Beijing-Tianjin-Hebei (BTH) region, which is the political and economic center of China. However, O3 has been measured in real time only over the past few years, and the observational records are discontinuous. Therefore, we propose a new method (WRFC-XGB) to establish a near-surface O3 concentration dataset in the BTH region by integrating the Weather Research and Forecasting with Chemistry (WRF-Chem) model with the extreme gradient boosting (XGBoost) algorithm. Based on this method, the 8-h maximum daily average (MDA8) O3 concentrations are obtained with full spatiotemporal coverage at a spatial resolution of 0.1° × 0.1° across the BTH region in 2018. Two evaluation methods, sample- and station-based 10-fold cross-validation (10-CV), are used to assess our method. The sample-based (station-based) 10-CV evaluation results indicate that WRFC-XGB can achieve excellent accuracy with a high coefficient of determination (R2) of 0.95 (0.91), low root mean square error (RMSE) of 13.50 (17.70) µg m−3, and mean absolute error (MAE) of 9.60 (12.89) µg m−3. In addition, superb spatiotemporal consistencies are confirmed for this model, including the estimation of high O3 concentrations, and our WRFC-XGB model outperforms traditional models and previous studies in data mining. In addition, the proposed model can be applied to estimate the O3 concentration when it has not been measured. Furthermore, the spatial distribution analysis of the MDA8 O3 in 2018 reveals that O3 pollution in the BTH region exhibits significant seasonality. Heavy O3 pollution episodes mainly occur in summer, and the high O3 loading is distributed mainly in the southern BTH areas, which will pose challenges to atmospheric environmental governance for local governments.

Multi-year variation of near-surface ozone at Zhongshan Station, Antarctica

With the support of the Chinese National Antarctic Research Expedition, near-surface ozone (O3) was continuously monitored at Zhongshan Station (ZOS) (69°22′12″ S, 76°21′49″ E, 18.5 m above sea level) in East Antarctica from 2008 to 2020. The seasonal and diurnal variability of near-surface O3 at ZOS were investigated. O3 enhancement events (OEEs) were frequently observed in the warm season (OEEs in January accounted for 23.0% of all OEEs). The OEEs at ZOS were related to the photochemical reaction processes under the influences of O3 and solar radiation in the stratosphere and synoptic-scale air mass transport from coastal areas (Princess Elizabeth Land, Wilkes Land, and Queen Mary Land), as evidenced by the recorded wind speed, solar shortwave irradiance, and total column ozone data and the computed potential source contribution function and concentration-weighted trajectory models. The results computed by the tool Stratosphere-to-Troposphere Exchange Flux indicated that stratosphere-to-troposphere transport had no direct impact on OEEs at ZOS. Therefore, synoptic-scale air mass transport is the main cause of OEEs in Antarctica, which is consistent with previous studies. Unlike OEEs at inland Antarctic stations, which are mainly affected by air mass transport from inland plateaus, OEEs at ZOS, a coastal station, are mainly affected by air mass transport from coastal land in East Antarctica.

Temporal and Spatial Variation in O3 Concentration Near the Surface of Shandong Peninsula and Analysis of Potential Source Areas

The purpose of this study was to explore the temporal and spatial distribution characteristics and potential sources of ozone (O3) in the Shandong Peninsula over a long period of time based on the analysis of the temporal and spatial changes in O3 concentration in Shandong Peninsula from 2005 to 2020. We used wavelet analysis, the entropy weight method, and correlation analysis to discuss O3 and its influencing factors and researched the potential sources of O3 in Shandong Peninsula. The results showed that:① in terms of the time pattern, the near-surface O3 in Shandong Peninsula showed a "triple peak" trend from 2005 to 2020, reaching the maximum value of[(40.48±7.64) μg·m-3] in 2010 and a minimum value of[(36.63±5.61) μg·m-3] in 2013. The season was expressed as:summer[(42.49±1.7) μg·m-3]>spring[(40.65±0.6) μg·m-3]>autumn[(36.47±0.7) μg·m-3]>winter[(36.46±0.3) μg·m-3]. ② In terms of the spatial pattern, the O3 concentration of Shandong Peninsula gradually increased with the increase in latitude from 2005 to 2020, showing the characteristics of high concentrations in the east and west and low in the middle region. During the 16-year evolution of the O3 concentration, there was a 1.5 a main oscillation period. ③The analysis of meteorological conditions revealed that O3 concentration was positively correlated with temperature, precipitation, relative humidity, and sunshine hours, whereas pressure and wind speed were negatively correlated. In the analysis of social factors, soot (dust) emissions were the most obvious factor affecting the third indicator, with a weight of 0.25. ④ Through simulating the trajectory of airflow from different regions (Ji'nan and Qingdao), it was found that the ocean airflow contributed 10.69% to Jinan and 48.94% to Qingdao. There was 64.04% of the long-distance air mass transmission path coming from the northwest, and 43.69% of the short-distance air mass transmission path was from the Bohai Sea and the Yellow Sea, followed by Shandong Province with 21.01%. ⑤ The analysis of potential sources of O3 showed that the potential sources of Ji'nan were mainly distributed in Jinzhou, Liaoning Province, northern Jiangsu Province, Hubei Province, and Anhui Province, with a WPSCF value >0.6, and Qingdao's WPSCF value of >0.6 was mainly distributed in the Yellow Sea area. The O3 contribution of Jining City, Linyi City, Xuzhou City, Huaibei City, and Lianyungang City was >40 μg·m-3. The area with >45 μg·m-3 in Qingdao was mainly in the Yellow Sea. Through the analysis of potential sources in the Shandong Peninsula, particular attention should be paid to the supply of industrial sources in the surrounding areas and the marine sources provided by marine air pollution.

Satellite-Based Diagnosis and Numerical Verification of Ozone Formation Regimes over Nine Megacities in East Asia

Urban photochemical ozone (O3) formation regimes (NOx- and VOC-limited regimes) at nine megacities in East Asia were diagnosed based on near-surface O3 columns from 900 to 700 hPa, nitrogen dioxide (NO2), and formaldehyde (HCHO), which were inferred from measurements by ozone-monitoring instruments (OMI) for 2014–2018. The nine megacities included Beijing, Tianjin, Hebei, Shandong, Shanghai, Seoul, Busan, Tokyo, and Osaka. The space-borne HCHO–to–NO2 ratio (FNR) inferred from the OMI was applied to nine megacities and verified by a series of sensitivity tests of Weather Research and Forecasting model with Chemistry (WRF-Chem) simulations by halving the NOx and VOC emissions. The results showed that the satellite-based FNRs ranged from 1.20 to 2.62 and the regimes over the nine megacities were identified as almost NOx-saturated conditions, while the domain-averaged FNR in East Asia was >2. The results of WRF–Chem sensitivity modeling show that O3 increased when the NOx emissions reduced, whereas VOC emission reduction showed a significant decrease in O3, confirming the characteristics of VOC-limited conditions in all of the nine megacities. When both NOx and VOC emissions were reduced, O3 decreased in most cities, but increased in the three lowest-FNRs megacities, such as Shanghai, Seoul, and Tokyo, where weakened O3 titration caused by NOx reduction had a larger enough effect to offset O3 suppression induced by the decrease in VOCs. Our model results, therefore, indicated that the immediate VOC emission reduction is a key controlling factor to decrease megacity O3 in East Asia, and also suggested that both VOC and NOx reductions may not be of broad utility in O3 abatement in megacities and should be considered judiciously in highly NOx-saturated cities in East Asia.

Inferring vertical variability and diurnal evolution of O3 formation sensitivity based on the vertical distribution of summertime HCHO and NO2 in Guangzhou, China

The vertical distributions of formaldehyde (HCHO) and nitrogen dioxide (NO2) and their indicative roles in ozone (O3) sensitivity are important for designing O3 mitigation strategies. Using hyperspectral remote sensing observations, tropospheric vertical profiles of HCHO, NO2, and aerosol extinction were investigated in Guangzhou, China from July to September 2019. On both O3 non-exceedance and polluted days, the HCHO and aerosol vertical profiles exhibited similar Gaussian shapes, but the NO2 profile exhibited an exponential decreasing shape. HCHO and aerosol were especially sensitive to O3 pollution, with higher values generally occurring at approximately noon and late afternoon at higher altitudes. We attempted to study the diurnal evolution of O3 sensitivity at different altitudes based on the HCHO to NO2 ratio (FNR) vertical profile. The FNR thresholds marking the transition regime (2.5 < FNR < 4.0) were derived from the relationship between the increase in O3 (∆O3) and FNR. Our results showed that O3 sensitivity tends to be VOC-limited both at lower (below approximately 0.4 km) and higher (above approximately 1.8 km) altitudes throughout the daytime. In the middle altitudes, the photochemical formation of O3 was mainly in the transition/NOx-limited regime in the morning and afternoon but in the VOC-limited regime at noontime. The relationship between TROPOMI column FNR and near-surface O3 sensitivity was further investigated. Compared with the MAX-DOAS near-surface FNR, slightly higher values of column FNR would increase the number of days classified as transition regimes, which was mainly caused by the inhomogeneous vertical distribution of HCHO and NO2 in the lower troposphere. This study provides an improved understanding of vertical variability and diurnal evolution of O3 formation sensitivity.

Impacts of strong El Niño on summertime near-surface ozone over China

The influences of strong El Niño events (1997/98 and 2015/16) on summertime near-surface ozone (O3) concentrations over China are investigated using the GEOS-Chem model. The results show that near-surface O3 concentrations increased by a maximum of 6 ppb (parts per billion) during the summer of the developing phase of the 1997/98 El Niño in northeastern China, mainly due to the increased chemical production related to the hot and dry conditions. Besides, the O3 concentration increased by 3 ppb during the developing summer of both the 1997/98 and 2015/16 El Niño in southern China. It was linked to the weakened prevailing monsoon winds, which led to the accumulation of O3 in southern China. In contrast, in the summer of the decaying phase of the two El Niño events, O3 concentrations decreased over many regions of China when the El Niño reversed to the cooling phase. This highlights that El Niño plays an important role in modulating near-surface O3 concentrations over China.摘要利用全球大气化学三维模式 (GEOS-Chem) 模拟研究两次强厄尔尼诺事件 (1997/98和2015/16) 对中国夏季近地面臭氧 (O3) 浓度的影响. 结果表明1997/98年厄尔尼诺事件发展期夏季中国东北区域O3浓度升高, 最大值超过6ppb, 这主要归因于高温晴朗低湿等气象因素导致O3化学生成升高. 此外, 两次厄尔尼诺事件发展期夏季O3浓度在中国南部均增加了3ppb, 这与盛行季风减弱导致中国南方O3局地积累有关. 相反, 在两次强厄尔尼诺衰减期夏季, 中国大部分地区O3浓度下降伴随着海温模态转变为拉尼娜事件. 这表明厄尔尼诺在调节中国近地面O3浓度中发挥着重要作用.

Influence of conducive weather on ozone in the presence of reduced NOx emissions: A case study in Chicago during the 2020 lockdowns

This study analyzes the response of near-surface O3 in Chicago to the COVID-19 lockdowns using observational data at the surface and from satellite. Even though the lockdowns caused NOx emissions to decrease by 18%, Chicago still experienced 17 high-O3 (>70 ppb) days in 2020, and the mean O3 mixing ratio did not show a significant change in 2020 compared with 2015–2019. Ozone production in summer 2020 in Chicago was in the “transitional” regime (HCHO/NO2 column ratio = 2.9), and not sensitive to changes in NOx in either direction. The primary driver for Chicago's O3 exceedances in 2020 was the dry tropical (DT) weather, which was associated with hot, dry, and stagnant meteorological conditions. There were 15 DT days in 2020, which led to more efficient production and greater accumulation of O3. The results suggest that a dramatic one-year 18% NOx reduction can be overcome by conducive meteorology and that NOx and VOC controls need to be more substantial and wide-ranging. This study also highlights the important role of different climate regimes, and not solely temperature, on the formation of O3.

Exploring Characteristics and Causes of Summer Ozone Pollution Based on Process Analysis in Wuhai

In recent years, summer O3 pollution has become more severe in Wuhai, where the terrain is complex and industrial parks are densely distributed. However, the characteristics and formation mechanisms of this pollution have not yet been investigated and remain unclear. Analyzing the variation and formation mechanisms of O3 is crucial to the prevention and control of air pollution in this region. By analyzing characteristics and using a WRF-CMAQ model to simulate three O3 pollution periods in Wuhai from June to August 2018, this study explored the causes of O3 pollution based on in-depth process analysis, and the effects of regional transportation and local photochemical reaction on O3 were also discussed. The diurnal variation of ozone exhibited a single-peak distribution, and near-surface O3 was positively correlated with short-wave radiation and temperature, and negatively correlated with relative humidity. The areas of Shizuishan in Ningxia and the Ulanbuhe desert exhibited high O3 values during the day, while the three industrial parks in Wuhai exhibited low values during both the day and night. Process analysis showed that transportation, chemical processes, and their relative magnitudes had a significant impact on O3. Local photochemical reactions and transport during the pollution period in June and July led to an obvious increase in O3, while the impact of chemical processes was about twice as large as that of transport. The increase of O3 in August was mainly caused by transport. Further decomposition of the transportation effect showed that transportation in the south and northwest directions had a remarkable effects on the increase of O3. Together with the emission of O3 precursors, the main sources of transportation were the Yinchuan, Shizuishan, and Bayannaoer regions. Therefore, Wuhai and neighboring cities should strengthen regional joint prevention and control by jointly formulating and implementing control measures for air pollution to reduce the impact of regional transmission on O3.

Competing effects of nitrogen deposition and ozone exposure on northern hemispheric terrestrial carbon uptake and storage, 1850–2099

Abstract. Tropospheric ozone (O3) and nitrogen deposition affect vegetation growth and, thereby, the ability of the land biosphere to take up and store carbon. However, the magnitude of these effects on the contemporary and future terrestrial carbon balance is insufficiently understood. Here, we apply an extended version of the O–CN terrestrial biosphere model that simulates the atmosphere to canopy transport of O3, its surface and stomatal uptake, the O3-induced leaf injury, and the coupled terrestrial carbon and nitrogen cycles. We use this model to simulate past and future impacts of air pollution against a background of concurrent changes in climate and carbon dioxide concentrations (CO2) for two contrasting representative concentration pathway (RCP) scenarios (RCP2.6 and RCP8.5). The simulations show that O3-related damage considerably reduced northern hemispheric gross primary production (GPP) and long-term carbon storage between 1850 and the 2010s. The simulated O3 effect on GPP in the Northern Hemisphere peaked towards the end of the 20th century, with reductions of 4 %, causing a reduction in the northern hemispheric carbon sink of 0.4 Pg C yr−1. During the 21st century, O3-induced reductions in GPP and carbon storage are projected to decline, through a combination of direct air pollution control methods that reduce near-surface O3 and the indirect effects of rising atmospheric CO2, which reduces stomatal uptake of O3 concurrent with increases of leaf-level water use efficiency. However, in hot spot regions such as East Asia, the model simulations suggest a sustained decrease in GPP by more than 8 % throughout the 21st century. O3 exposure reduces projected carbon storage at the end of the 21st century by up to 15 % in parts of Europe, the US, and East Asia. Our simulations suggest that the stimulating effect of nitrogen deposition on regional GPP and carbon storage is lower in magnitude compared to the detrimental effect of O3 during most of the simulation period for both RCPs. In the second half of the 21st century, the detrimental effect of O3 on GPP is outweighed by nitrogen deposition, but the effect of nitrogen deposition on land carbon storage remains lower than the effect of O3. Accounting for the stimulating effects of nitrogen deposition but omitting the detrimental effect of O3 may lead to an overestimation of projected carbon uptake and storage.

Spatiotemporal Changes of Near-Surface Ozone Concentration From 2015 to 2018 in Beijing

In this study, we investigated the spatiotemporal changes of near-surface O3 concentration based on 33 automatic air quality monitoring stations in Beijing in 2015 and 2018. Here we show that the diurnal variations for O3 concentration at 33 monitoring stations exhibited a single-peak mode with a minimum concentration from 06:00 to 07:00 and a maximum value from 14:00 to 15:00. We find that the O3 concentration was significantly positively correlated with the air temperature, solar total radiation, and wind speed, while it was negatively correlated with the relative humidity. Among those factors, the air temperature played the most important role in influencing O3 concentration (relative contribution is greater than 88% in the boosted regression trees model). We also present that the annual variation of O3 concentration at all stations tended to be a “bell-shaped” curve distribution with a peak in summer and the lowest value in winter. The annual averaged O3 concentration at 33 stations in Beijing was 57.5 ± 9.8 μg⋅m−3 in 2015 and 60.3 ± 9.0 μg⋅m−3 in 2018. In addition, we detect that the annual averaged value of the O3 concentration was lower in the central and southern Beijing, and higher in the northern Beijing both in 2015 and 2018. The spatial difference of the O3 concentration could be explained by the traffic pollution, vegetation coverage, atmospheric regional transmission, and atmospheric particulate matter concentration.