Surface Ozone Research Articles

Impact of Landes forest fires on air quality in France during the 2022 summer

Abstract. The atypical huge forest fires observed in France during the summer of 2022 are modeled using the CHIMERE model. The impact of these emissions is quantified on ozone, aerosols and aerosol optical depth (AOD). The fires also influence the surface by destroying the vegetation and creating new erodible surfaces. This increases the mineral dust emissions but also reduces the leaf area index (LAI), and then it decreases the biogenic emissions and the dry deposition of gases such as ozone. Results show that the fires induce numerous increases in surface ozone and particulate matter (PM) concentrations close to the sources but also in downwind remote sites such as the Paris area. During the period of the most intense fires in July, the impact of concentrations is mainly due to emissions themselves, and later, in August, ozone and PM concentrations continue to increase but this time due to changes in the burned surfaces.

Stratospheric influences on surface ozone increase during the COVID-19 lockdown over northern China

Surface ozone increased unexpectedly over northern China during the COVID-19 lockdown (CLD) period (23 January–29 February 2020), which was characterized by vigorous emission reduction. The reasons for this ozone enhancement have been speculated from perspectives of chemical responses to the emissions and meteorology. As known, the processes of natural stratospheric ozone injecting to the troposphere are most active in winter and spring. Yet, little attention was paid to stratospheric influences on this ozone enhancement. Here we report a stratospheric intrusion (SI) that reached the surface over northern China on 15–17 February during the CLD. The coevolution of enhanced ozone and sharply declined carbon monoxide and relative humidity (RH) was indicative of the SI occurrence. We show that the SI was facilitated by a cutoff low system that led to abnormally high surface ozone in most part of northern China. We estimate that over the SI period, the injected stratospheric ozone constituted up to 40–45% of the surface ozone over northern China. If the stratospheric ozone inputs were scaled over the entire CLD period, these inputs would account for 4–8% of the surface ozone. In view of the unexpected ozone increase during the CLD, this SI event could explain up to 18% of the ozone increase in some cities, and average 5–10% over larger areas that were affected. Hence, the nonnegligible stratospheric influences urge extra consideration of natural ozone sources in disentangling the role of emission reduction and meteorological conditions during the CLD in China and elsewhere in the world.

Observations and explicit modeling of summer and autumn ozone formation in urban Beijing: Identification of key precursor species and sources

Due to the complexity and nonlinearity of the ozone (O3) production, it is vital to understand the detailed knowledge of ozone–precursor relationship for the formulation of effective mitigation of surface ozone pollution. In this study, continuous measurements of O3, volatile organic compounds (VOCs), and related parameters were conducted at an urban site of Beijing in the summer and autumn of 2019. The photochemical box model contained the Master Chemical Mechanism (MCMv3.3.1) was used to reveal the detailed information on the photochemical O3 formation. Results show that the average concentration of total VOCs (TVOC) was 31.2 ± 10.7 ppb and 37.8 ± 18.9 ppb during the summer and autumn campaign, respectively, with the largest contribution from alkanes in both seasons, which mainly originated from liquefied petroleum gas (LPG) usage (20.2%–22.6%), gasoline vehicular exhaust (21.0%–21.6%), diesel vehicular exhaust (18.1%–18.3%), solvent usage (20.4%–24.1%), and fuel evaporation (16.4%–17.4%) that identified by positive matrix factorization (PMF) model. Heavy ozone pollution episodes were observed and the net local O3 production rate during summer (EP1) and autumn (EP2) pollution episode was 9.87 ± 0.62 ppbv h−1, and 9.44 ± 1.18 ppbv h−1, respectively, which was both dominated by the reaction between HO2 with NO. The analysis of relative incremental reactivity (RIR) and O3-NOx-VOC isopleth shows that ozone formation was VOC-limited in urban Beijing, with alkenes and aromatics contributed the most to O3 formation in summer and autumn, respectively. In addition, modellings for various emission reduction scenarios were carried out, indicating the reduction of gasoline vehicles emissions in summer and both reduction of gasoline vehicles and solvent usage emissions in autumn is the best measures to efficiently reduce O3 pollution. These results improved our understanding of O3 precursors and their impact on ozone production and provided a more targeted reference for controlling ozone pollution in Beijing.

Relationship between summer time near-surface ozone concentration and planetary boundary layer height in Beijing

The planetary boundary layer height (PBLH) is critical in affecting the concentration of air pollutants at surface. The relationship between PBLH and surface ozone concentration can be complicated but not entirely clear. In this study, by using observations and WRF-Chem simulations, we explore the relationship between the surface ozone and the PBLH in the summer daytime in Beijing, a major global ozone pollution hotspot. It is found that the surface ozone-PBLH relationship exhibits a three-stage evolution with ozone: first, increasing with PBLH, then keeping steady, and finally falling. The two turning points are around 1000 and 2000 m respectively. This process is likely controlled by the different contributions of chemical production and vertical mixing. Specifically, when PBLH is below ∼1000 m, as PBLH increases, chemical production increases owing to the light enhancement whereas the ozone contribution from vertical mixing remains weak due to the decreased ozone concentration gradient between the surface and the upper layer, resulting in a net gain of surface ozone concentration. When the PBL continues to rise, chemical production contributes less mainly due to the decrease of ozone precursors at the surface, whereas vertical mixing becomes more vigorous that further diluting surface ozone, resulting in a net loss of surface ozone concentration, especially when PBLH reaches above ∼2000 m. Our results contribute to understanding the variability of surface ozone in Beijing area and provide insights for local ozone air quality control.

Assessing surface ozone risk to human health and forests over time in Poland

Hourly ground-level ozone (O3) data from 52 monitoring stations in Poland were analyzed over a ten-year pre-COVID19 period (2010–2019) to map and define areas at risk for human health and vegetation, and to calculate trends over the study period. Annual O3 metrics (24-h average concentrations, 50th percentiles, and hourly maxima), human health metrics (Sum Of daily maximum 8-h Means Over 35 ppb, SOMO35, summertime average of the daily 8-h maximum O3 concentrations, O3 MDA8, and number of daily maximum 8-h values above 60 ppb, EU60) and vegetation exposure metrics (AOT40, i.e., accumulation of hourly O3 concentrations exceeding 40 ppb during the growing season for agricultural crops AOT40c and forests AOT40f) were investigated. Higher O3 levels occurred in rural areas than in cities. Between 2010 and 2019, the O3 levels were rising in both urban and rural areas. Despite the reduction of nitrogen oxides (NOx: - 2.33% year-1) and volatile organic compounds emissions (VOCs: - 0.95% year-1), annual O3 mean levels (+0.81 and +0.12% year-1), 50th percentiles (+1.06 and ∼0% year-1), hourly maxima (- 0.10 and +0.23% year-1), SOMO35 (+2.86 and +1.50% year-1), summertime O3 MDA8 (+0.49 and +0.48% year-1), EU60 (+0.09 and +0.15 days year-1), AOT40c (+3.79 and +3.29% year-1) and AOT40f (+4.47 and +4.34% year-1) commonly increased in urban and rural stations. The O3 levels increased at 75.0% of urban stations and 62.5% of rural stations. A slight decline of the number of O3 peaks occurred in cities, likely driven by the recent reductions in NOx emissions by on-road transport. For all metrics, the increase can be attributed to higher regional photochemical O3 formation and rising background O3 levels likely driven by imported O3 and its precursors by long-range transport, climate change, and lower O3 titration by NOx emissions decline. The failure to attain the target value for O3 for protecting vegetation and human health and vegetation persists. Southeastern Poland, where coal stoves are still used for residential heating, faces the highest O3 risk. This study reports new information on surface O3 levels, exceedances, and trends in Poland to develop effective policies to mitigate O3 effects.

A signature of aged biogenic compounds detected from airborne VOC measurements in the high arctic atmosphere in March/April 2018

During the PAMARCMiP 2018 campaign (March and April 2018) a proton-transfer-reaction mass spectrometer (PTR-MS) was deployed onboard the POLAR 5 research aircraft and sampled the high Arctic atmosphere under Arctic haze conditions. More than 100 compounds exhibited levels above 1 pmol/mol in at least 25% of the measurements. We used acetone mixing ratios, ozone concentrations, and back trajectories to identify periods with and without long-range transport from continental sources. During two flights, surface ozone depletion events (ODE) were observed that coincided with enhanced levels of acetone, and methylethylketone, and ice nucleating particles (INP).Air masses with continental influence contained elevated levels of compounds associated with aged biogenic emissions and anthropogenic pollution (e.g., methanol, peroxyacetylnitrate (PAN), acetone, acetic acid, methylethylketone (MEK), proprionic acid, and pentanone). Almost half of all positively detected compounds (>100) in the high Arctic atmosphere can be associated with terpene oxidation products, likely produced from monoterpenes and sesquiterpenes emitted from boreal forests. We speculate that the transport of biogenic terpene emissions may constitute an important control of the High Arctic aerosol burden. The sum concentration of the detected aerosol forming vapours is ∼12 pmol/mol, which is of the same order than measured dimethylsulfide (DMS) mixing ratios and their mass density corresponds to approximately one fifth of the measured non-black-carbon particles.

Prediction of daily PM2.5 and ozone based on high-density weather stations in China: Nonlinear effects of meteorology, human and ecosystem health risks

In recent decade, despite the implementation of strict emission reductions, PM2.5 and surface ozone (O3) in China are still at high pollution level. In this study, based on observations at air quality stations (∼1500 mainly in urban region), daily PM2.5 and MDA8 (the daily maximum 8 h average) O3 concentrations in high-density and uniform meteorological sites (∼2000) over China during 2017–2019 were retrieved using generalized additive models (GAMs) for different regions on a seasonal scale, in order to establish 0.1° gridded datasets and investigate their spatiotemporal characteristics, nonlinear effects of meteorology, and ambient air pollution-attributable health risks on a regional scale. This model can provide high accuracy in the estimation of daily PM2.5 (O3) in 2018 with overall cross-validation R2 and RMSE of 0.81 (0.80) and 12.73 (17.63) μg/m3 and predictive capability in 2017 and 2019 with R2 of 0.67 (0.70) for PM2.5 (O3). Temperature, relative humidity and visibility are three main meteorological factors driving PM2.5 (O3) response. PM2.5 generally exhibits an exponential decrease with increasing visibility and an increase with increasing relative humidity, while is suppressed at the thresholds of 60% and 70%. For O3, in northern China, positive response of temperature is more important and O3 suppression exists at 36 °C ∼ 41.5 °C, whereas negative response of relative humidity is dominating in southern China. Overall, annual averaged PM2.5 (O3) values across China reduced (increased) by 18.7% (11.2%) between 2017 and 2019, with the highest concentrations and variation in North China. These variations contributed to a 14.9% reduction in PM2.5 attributed premature deaths, but a 10.4% increase in O3 exposure related deaths. Generally, central-eastern China still exists greater health risk with per capita premature mortality ranging from 0.80‰ to 1.19‰ for PM2.5 and 1.91‰ to 2.60‰ for O3. Additionally, O3 vegetation damages demonstrate a decline (increase) by 1.3% (21.7%) in North China with higher O3 pollution (southern China with slight pollution) between 2017 and 2019. These findings highlight the essentiality for the synergistic control of PM2.5 and O3 based on regional differences in China.

Were Wildfires Responsible for the Unusually High Surface Ozone in Colorado During 2021?

AbstractGround‐level ozone (O3) was unusually high in northern Colorado in the summer of 2021 with maximum daily 8‐hr average (MDA8) concentrations 6 to 8 parts‐per‐billion by volume (ppbv) higher than in 2019, 2020, or 2022. One or more of the monitors on the Colorado Front Range exceeded the 2015 U.S. National Ambient Air Quality Standard (NAAQS) of 70 ppbv on 66 of the 122 days from 1 June to 30 September, and this record number of exceedances coincided with the near daily presence of dispersed smoke haze from wildfires in Arizona, California, and the Pacific Northwest. In this paper, we use regulatory and non‐regulatory surface O3 and PM2.5 measurements in conjunction with ground‐based lidar observations to estimate how much O3 was associated with the wildfire smoke. Analyses of the surface measurements suggest that pyrogenic O3 transported to northern Colorado with the smoke increased the surface concentrations in northern Colorado by an average of 8 ppbv in July, 3 ppbv in August, and 2 ppbv in September. Analysis of the lidar measurements showed these contributions to be as large as 12 ppbv on some days. Production of O3 from reactions of pyrogenic VOCs and locally emitted NOx appears to have been minimal (<3 ppbv) in the Boulder area, but may have been much larger in the suburbs southwest of downtown Denver.

Unraveling spatiotemporal patterns and multiple driving factors of surface ozone across China and its urban agglomerations management strategies

Since State Council launched the Action Plan for Air Pollution Prevention and Control in 2013, national concentration of fine particulate matter (PM2.5) has continued to decline in China, while surface ozone (O3) pollution shows an obvious rise. To identity hot regions and develop targeted policy, the spatiotemporal O3 variation and its population-weighted exposure features were analyzed in 337 cities across China, using autocorrelation analysis and grid exposure calculation. In the identified hot urban agglomerations, the correlation analysis and geographic weighted regression model (GWR) were used to study related meteorological factors and socioeconomic driving factors. O3 pollution and its human exposure were found to have significant spatial aggregation characteristics, showing a need for regional management policy. Beijing-Tianjin-Hebei Urban Agglomeration (BTH-UA), Central Plains Urban Agglomeration (CP-UA), and Yangtze River Delta Urban Agglomeration (YRD-UA) were identified as hot regions where O3 concentration exceeded 160 μg·m−3, exceedance rate was over 20% and population-weighted exposure risk was relatively high. Correlation analysis in the hot regions indicated high surface temperature, low relative humidity, and low wind speed were positive to O3 increase. Further, GWR results revealed that O3 in the majority of cities was positively related with population density (PD), the per capita GDP (Per_GDP), industrial soot emissions (ISE), industrial SO2 emissions (ISO2), and average annual concentration of inhaled fine particulate matter (PM10), and negatively related with total land area of administrative region (Administration) and area of green land (Green). From the regional driving factor difference, the targeted UA management policy was provided.

The effect of anthropogenic emission, meteorological factors, and carbon dioxide on the surface ozone increase in China from 2008 to 2018 during the East Asia summer monsoon season

Abstract. Despite the implementation of the Clean Air Action Plan by the Chinese government in 2013, the issue of increasing surface ozone (O3) concentrations remains a significant environmental concern in China. In this study, we used an improved regional climate–chemistry–ecology model (RegCM-Chem-YIBs) to investigate the impact of anthropogenic emissions, meteorological factors, and CO2 changes on summer surface O3 levels in China from 2008 to 2018. Compared to its predecessor, the model has been enhanced concerning the photolysis of O3 and the radiative impacts of CO2 and O3. The investigations showed anthropogenic emissions were the primary contributor to the O3 increase in China, responsible for 4.08–18.51 ppb in the North China Plain. However, changed meteorological conditions played a crucial role in decreasing O3 in China and may have a more significant impact than anthropogenic emissions in some regions. Changed CO2 played a critical role in the variability of O3 through radiative forcing and isoprene emissions, particularly in southern China, inducing an increase in O3 on the southeast coast of China (0.28–0.46 ppb) and a decrease in southwest and central China (−0.51 to −0.11 ppb). Our study comprehensively analyzed O3 variation across China from various perspectives and highlighted the importance of considering CO2 variations when designing long-term O3 control policies, especially in high-vegetation-coverage areas.

Decadal changes in the relationship between Arctic stratospheric ozone and sea surface temperatures in the North Pacific

Using multi-source observations and ERA-Interim reanalysis data, this study found that the relationship between Arctic stratospheric ozone in March and North Pacific sea surface temperature (SST) in April shows dramatic decadal changes, and it significantly weakens since the 2000s. By enhancing the stratospheric circulations, a decreased Arctic stratospheric ozone favors tropospheric positive Arctic Oscillation (+AO)-like anomaly during PRE eras (1979–1999), with positive geopotential height (GH) anomalies over high-latitude Asia. The stratospheric ozone anomaly also favors the Asian positive GH anomalies via modulating high cloud and its related longwave radiation. According to geostrophic wind relationships, the Asian positive GH anomalies are accompanied by easterly anomalies over midlatitude Asia in late March, which further extend eastward and thereby induce easterly anomalies over the midlatitude North Pacific. The North Pacific easterly anomalies result in negative North Pacific Oscillation (–NPO)-like anomaly via vorticity forcing of zonal wind and the interactions between synoptic-scale eddies and mean flow, forcing significant SST anomalies. However, during POST eras (2000–2019), firstly, the +AO-related positive GH anomalies over high-latitude Asia are relatively weak, accompanied by weak easterly anomalies over midlatitude Asia according to geostrophic wind relations, which induce weak easterly anomalies over the North Pacific. Secondly, a westerly anomaly occurs over the midlatitude North Pacific, which partly offsets the easterly anomalies from Asia, weakening the North Pacific easterly anomalies. The weak easterly anomalies further induce weak –NPO and SST anomalies during the POST eras. Our analysis further indicates that the North Pacific westerly anomalies and weakening of the positive GH anomalies over high-latitude Asia associated with ozone are related to the interference of the westerly phase of quasi-biennial oscillation and the weakened stratospheric ozone anomaly over high-latitude Asia, respectively.

Development of a CMAQ–PMF-based composite index for prescribing an effective ozone abatement strategy: a case study of sensitivity of surface ozone to precursor volatile organic compound species in southern Taiwan

Abstract. Photochemical ozone pollution is a serious air quality problem under weak synoptic conditions in many areas worldwide. Volatile organic compounds (VOCs) are largely responsible for ozone production in urban areas where nitrogen oxide (NOx) mixing ratios are high while usually not a limiting precursor to ozone (O3). In this study, the Community Multiscale Air Quality model higher-order decoupled direct method (CMAQ-HDDM) at an urban-scale resolution (1.0 km×1.0 km) in conjunction with positive matrix factorization (PMF) was used to identify the dominant sources of highly sensitive VOC species to ozone formation in southern Taiwan, a complex region of coastal urban and industrial parks and inland mountainous areas. First-order, second-order, and cross sensitivities of ozone concentrations to domain-wide (i.e., urban, suburban, and rural) NOx and VOC emissions were determined for the study area. Negative (positive) first-order sensitivities to NOx emissions are dominant over urban (inland) areas, confirming ozone production sensitivity favors the VOC-limited regime (NOx-limited regime) in southern Taiwan. Furthermore, most of the urban areas also exhibited negative second-order sensitivity to NOx emissions, indicating a negative O3 convex response where the linear increase of O3 from decreasing NOx emissions was largely attenuated by the nonlinear effects. Due to the solidly VOC-limited regime and the relative insensitivity of O3 production to increases or decreases of NOx emissions, this study pursued the VOC species that contributed the most to ozone formation. PMF analysis driven by VOCs resolved eight factors including mixed industry (21 %), vehicle emissions (22 %), solvent usage (17 %), biogenic sources (12 %), plastic industry (10 %), aged air mass (7 %), motorcycle exhausts (7 %), and manufacturing industry (5 %). Furthermore, a composite index that quantitatively combined the CMAQ-HDDM sensitivity coefficient and PMF-resolved factor contribution was developed to identify the key VOC species that should be targeted for effective ozone abatement. Our results indicate that VOC control measures should target (1) solvent usage for painting, coating and the printing industry, which emits abundant toluene and xylene; (2) gasoline fuel vehicle emissions of n-butane, isopentane, isobutane, and n-pentane; and (3) ethylene and propylene emissions from the petrochemical industry.

Impacts of COVID-19 Lockdown on Air Quality in Shenzhen in Spring 2022

The short-term reduction of air pollutant emissions is an important emergency control measure for avoiding air pollution exceedances in Chinese cities. However, the impacts of short-term emission reductions on the air qualities in southern Chinese cities in spring has not been fully explored. We analyzed the changes in air quality in Shenzhen, Guangdong before, during, and after a city-wide lockdown associated with COVID-19 control during March 14 to 20, 2022. Stable weather conditions prevailed before and during the lockdown, such that local air pollution was strongly affected by local emissions. In-situ measurements and WRF-GC simulations over the Pearl River Delta (PRD) both showed that, due to reductions in traffic emissions during the lockdown, the concentrations of nitrogen dioxide (NO2), respirable particulate matter (PM10), and fine particulate matters (PM2.5) in Shenzhen decreased by (-26±9.5)%, (-28±6.4)%, and (-20±8.2)%, respectively. However, surface ozone (O3) concentration did not change significantly[(-1.0±6.5)%]. TROPOMI satellite observations of formaldehyde and nitrogen dioxide column concentrations indicated that the ozone photochemistry in the PRD in spring 2022 was mainly controlled by the volatile organic compound (VOCs) concentrations and was not sensitive to the reduction in nitrogen oxide (NOx) concentrations. Reduction in NOx may even have increased O3, because the titration of O3 by NOx was weakened. Due to the small spatial-temporal extent of emission reductions, the air quality effects caused by this short-term urban-scale lockdown were weaker than the air quality effects across China during the widespread COVID-19 lockdown in 2020. Future air quality management in South China cities should consider the impacts of NOx emission reduction on ozone and focus on the co-reduction scenarios of NOx and VOCs.

Downwind Ozone Changes of the 2019 Williams Flats Wildfire: Insights From WRF‐Chem/DART Assimilation of OMI NO2, HCHO, and MODIS AOD Retrievals

AbstractThis study investigates the impacts of the Williams Flats wildfire (August 3‐9, 2019) on ozone conccentrations and chemistry in the downwind region using an assimilation framework with satellite retrievals and meterological measurements. By assimilating satellite‐retrieved nitrogen dioxide (NO2) and formaldehyde (HCHO) columns, we improve surface ozone simulations (index of agreement of 0.94 compared to station measurements) and utilize aerosol optical depth (AOD) retrievals to simulate spatial dynamics of wildfire plumes better. Comparing simulated ozone with the Fire Influence on Regional to Global Environments and Air Quality aircraft measurements reveals a fair simulation of ozone in smoke and non‐smoke plumes within the lower troposphere (7.00 ppbv mean absolute error). Comparing near‐distance and far‐distance locations, the study observed higher‐than‐average concentrations of nitrogen oxides, peroxyacetyl nitrate, nitric acid, and oxygenated volatile organic compounds due to wildfire emissions, which increased ozone concentrations by 3–5 ppbv during the wildfire in near‐distance locations and 2–3 ppbv in far‐distance locations. During more intense wildfire days, above 120 ppbv carbon monoxide plumes transported over the Rocky Mountains to the east. Ozone regime indicators showed a clear transition area downwind of the wildfire region that exacerbated the formation of ozone downwind. Our findings suggest that a joint assimilation of NO2 column, HCHO column, and AOD can enhance our understanding of wildfire‐associated ozone chemistry and dynamics.

Future climate change impacts on U.S. agricultural yields, production, and market.

This study provides estimates of climate change impacts on U.S. agricultural yields and the agricultural economy through the end of the 21st century, utilizing multiple climate scenarios. Results from a process-based crop model project future increases in wheat, grassland, and soybean yield due to climate change and atmospheric CO2 change; corn and sorghum show more muted responses. Results using yields from econometric models show less positive results. Both the econometric and process-based models tend to show more positive yields by the end of the century than several other similar studies. Using the process-based model to provide future yield estimates to an integrated agricultural sector model, the welfare gain is roughly $16B/year (2019 USD) for domestic producers and $6.2B/year for international trade, but domestic consumers lose $10.6B/year, resulting in a total welfare gain of $11.7B/year. When yield projections for major crops are drawn instead from econometric models, total welfare losses of more than $28B/year arise. Simulations using the process-based model as input to the agricultural sector model show large future production increases for soybean, wheat, and sorghum and large price reductions for corn and wheat. The most important factors are those about economic growth, flooding, international trade, and the type of yield model used. Somewhat less, but not insignificant factors include adaptation, livestock productivity, and damages from surface ozone, waterlogging, and pests and diseases.

СОДЕРЖАНИЕ ОЗОНА НАД ТЕРРИТОРИЕЙ РОССИЙСКОЙ ФЕДЕРАЦИИ В ПЕРВОМ КВАРТАЛЕ 2023 Г

The review is compiled on the basis of the results of operation of the total ozone (TO) monitoring system in the CIS and Baltic countries functioning in operational mode at Central Aerological Observatory (CAO). The monitoring system uses data from the national network equipped with M-124 filter ozonometers being under the methodological supervision of Main Geophysical Observatory. The quality of the functioning of the entire system is operationally controlled in CAO based on the OMI satellite equipment observations (NASA, USA). Basic TO observation data are generalized for each month of the first quarter of 2023 and for the first quarter. Data of routine observations of surface ozone values in the Moscow region are also presented.

Coupled mesoscale–microscale modeling of air quality in a polluted city using WRF-LES-Chem

Abstract. To perform realistic high-resolution air quality modeling in a polluted urban area, the Weather Research and Forecasting (WRF) model is used with an embedded large-eddy simulation (LES) module and online chemistry. As an illustration, a numerical experiment is conducted in the megacity of Hong Kong, which is characterized by multi-type inhomogeneous pollution sources and complex topography. The results from the multi-resolution simulations at mesoscale and LES scales are evaluated by comparing them with ozone sounding profiles and surface observations. The comparisons show that both mesoscale and LES simulations reproduce the mean concentrations of the chemical species and their diurnal variations at the background stations well. However, the mesoscale simulations largely underestimate the NOx concentrations and overestimate O3 at the roadside stations due to the coarse representation of the traffic emissions. The LES simulations improve the agreement with the measurements near the road traffic, and the LES with the highest spatial resolution (33.3 m) provides the best results. The large-eddy simulations show more detailed structures in the spatial distributions of chemical species than the mesoscale simulations, highlighting the capability of LES to resolve high-resolution photochemical transformations in urban areas. Compared to the mesoscale model results, the LES simulations show similar evolutions in the profiles of the chemical species as a function of the boundary layer development over a diurnal cycle.

Evolution of summer surface ozone pollution patterns in China during 2015–2020

Surface ozone is one of the most severe air pollutants in China and is influenced by meteorological processes on multiple scales. By identifying the two dominant patterns of ozone pollution through Empirical Orthogonal Functions method, we show here that the widespread pollution processes in China may be closely related to high-pressure anomaly in North China and low-pressure anomaly in the western Pacific, respectively. The positive time period of the first pattern (PC1P) extracts the distribution characteristics of the most severe periods of ozone pollution in summer time. It is physically linked to the high-pressure anomaly in North China centered on the Huanghuai Region, which eventually induced the high-temperature anomaly and low-humidity anomaly that enhanced the photochemical reactions to elevate the ozone levels. The spatial and temporal evolution of ozone pollution during this meteorological process shows a uniform pollution characteristic in the northern region and a higher increase in ozone concentration in the Huanghuai Region. The positive time period of the second pattern (PC2P) is associated with the variation of the low-pressure anomaly in the western Pacific. It indicates uniformly high ozone pollution in the south, especially in the Yangtze River Delta, the middle reaches of the Yangtze River (MYR) and the Pearl River Delta. Our results highlight that summer ozone pollution in eastern China is closely related to weather patterns. In addition, it is noteworthy that in the positive time period, the annual growth trends of Huanghuai Region in the first pattern (PC1P) and MYR in the second pattern (PC2P) are significantly higher than the growth trends of the megacity clusters, which requires the attention of relevant policy-making authorities.

Driving Forces of Meteorology and Emission Changes on Surface Ozone in the Huaihe River Basin, China.

The online version contains supplementary material available at 10.1007/s11270-023-06345-1.

The Stratosphere-to-Troposphere Transport Related to Rossby Wave Breaking and Its Impact on Summertime Ground-Level Ozone in Eastern China

In summertime, eastern China experiences severe ozone pollution. Stratosphere-to-troposphere transport (STT), as the primary natural source of tropospheric ozone, may have a non-negligible contribution to ground-level ozone. Rossby wave breaking (RWB) is a leading mechanism that triggers STT, which can be categorized as anticyclonic wave breakings (AWBs) and cyclonic wave breakings (CWBs). This study uses an objective method to diagnose AWBs and CWBs and to investigate their influence on the surface ozone in eastern China using ground-based ozone observations, satellite ozone data from AIRS, a stratospheric ozone tracer simulated by CAM-chem, and meteorological fields from MERRA-2. The results indicate that AWBs occur mainly and frequently over northeast China, while CWBs occur mostly over the northern Sea of Japan. STTs triggered by AWBs mainly have sinking areas over the North China Plain, increasing the ground-level ozone concentrations by 5–10 ppbv in eastern China. The downwelling zones in the CWBs extend from Mongolia to the East China Sea, potentially causing an elevation of 5–10 ppbv of ozone in both central and eastern China. This study gives an overview of the impacts of AWBs and CWBs on surface ozone in eastern China and helps to improve our understanding of summertime ozone pollution in eastern China.