Regional Ozone Research Articles

Higher contribution of coking sources to ozone formation potential from volatile organic compounds in summer in Taiyuan, China

Regional ozone pollution has become one of the most challenging environmental problems in China. In July 2019, hourly real-time monitoring of ozone (O3) and nitrogen oxides (NOx) and 3-hour off-line measurement of volatile organic compounds (VOCs) during a 10-day intensive campaign were conducted at four sites in Taiyuan, Shanxi Province, China. The average mixing ratio of total VOCs (including alkanes, alkenes, aromatics and acetylene) was 14.8 ± 2.8 ppbv and the dominant VOCs species to O3 formation were alkenes in Taiyuan. According to China Ambient Air Quality Standard Grade II (hourly averaged mixing ratio of 103 ppbv), the studied periods were divided into O3 attainment periods (EP1) and O3 pollution periods (EP2). A continuous O3 pollution event was captured during 12–15 July, with the maximum hourly O3 mixing ratio of 131.7 ppbv. Higher temperature, lower relative humidity, weaker winds and local photochemical reaction were conducive to O3 pollution during EP2. The analysis of VOCs/NOx ratio indicated that the formation of O3 was co-controlled by both VOCs and NOx during the period of 12:00–18:00 LT (high value period of O3), and it was controlled by VOCs during the remaining period. The abundances, compositions of typical VOCs and VOCs/NOx ratio showed clear spatial and temporal variations. Six major sources of VOCs were identified by positive matrix factorization, including coal and biomass combustion (33%), coking sources (28%), vehicular emissions (14%), solvent usage (10%), industrial processes (8%) and biological sources (7%). Backward trajectory analysis found that higher concentration of O3 in air masses from local (70%) and southern areas (22.5%) during EP2. Local (32%) and southern (30%) coking sources were the main contributors of ozone formation potential (OFP) during EP2.

Synoptic and meteorological drivers of regional ozone pollution events in China

Surface ozone (O3) pollution events are becoming more frequent and have recently emerged as a severe air pollution problem in China. However, the spatial–temporal distribution of surface O3, as well as its primary synoptic and meteorological drivers, remains poorly understood. The purpose of this study was to identify the key synoptic and meteorological drivers of O3 pollution in different regions of China. To achieve this goal, this study established meteorology overlaps of regional O3 pollution events in space and time and applied a comprehensive statistical model selection method for optimal synoptic and meteorological models, based on a newly released O3 dataset for 2015–2018. It was observed that extreme regional O3 pollution events (duration >7 d) occurred more frequently and exhibited a high co-occurrence frequency (>50%) with air stagnation (AS). Moreover, the beginning and end of 69% of the regional O3 pollution events coincided with regional daily maximum temperature changes. The intensity of AS is the dominant driver of O3 pollution event intensity across most of the six selected megacity regions. Although other meteorological drivers, such as the intensity of hot days (HD) and meridional wind of 10 m were also important, their impacts varied according to the region. Overall, increase in extreme AS and HD led to the worsening of regional O3 pollution events. These findings imply that mitigating regional O3 pollution should consider changing synoptic and meteorological conditions.

Effect of dynamic low DREs from flare combustion on regional ozone pollution during a chemical plant shutdown

The destruction and removal efficiencies (DREs) for industrial flare combustion could be, in reality, less than the supposed standard values of 98%/99% because of various atmospheric and plant operating conditions. Thus, flaring during chemical plant shutdown (CPS) under low DREs would release larger quantities of VOCs and NOx than expected, which might rapidly worsen the regional ozone pollution under solar radiation. Therefore, it is vital to examine the quantity and sensitivity of ozone impacts owing to low DREs for flare combustion rather than standard values. In this paper, effect of dynamic low DREs on regional ozone impacts during CPS flaring has been systematically conducted by coupling Aspen Plus with CAMx modeling and simulation. Case studies indicated that 8-hr ozone caused by CPS flaring under low DREs could range from 6.08 to 7.28 ppb, which was much greater than that based on the standard DREs ranging from 1.8 to 2.19 ppb. This study also demonstrated that the 8-hr ozone increment could be significantly reduced from the maximum of 6.14 ppb to the minimum of 0.85 ppb by starting the CPS operations at the optimal time. Another important finding was that ozone impacts might slightly increase with the increase of flare stack height due to meteorological conditions including high wind speed and strong solar radiation. This study would provide scientific support for quantitative ozone evaluation caused by CPS flare emissions, which will enrich future solutions for cost-effective regional air-quality management and ozone pollution control.

Source Apportionment of Regional Ozone Pollution Observed at Mount Tai, North China: Application of Lagrangian Photochemical Trajectory Model and Implications for Control Policy

AbstractTo better understand the characteristics and trace the sources of regional ozone (O3) in the North China Plain (NCP), we analyzed 1‐year continuous observations obtained at Mount Tai in 2018 and compared with previous data from 2006–2009. In the warm seasons (April–September), O3 pollution (defined as a maximum daily 8‐h average O3 mixing ratio that exceeds 75 ppbv) occurred frequently (59%–92% of days) and O3 concentrations significantly increased (especially in July–September) from 2006–2009 to 2018. We applied the Lagrangian photochemical trajectory model, built on the coupling of the Lagrangian backward trajectory model and Master Chemical Mechanism box model, to identify the source regions, key precursors, and emission sectors. The NCP was identified as the major source region with an average contribution of 74% ± 27% to the regional O3 concentrations during the O3 episodes in April–September. Regional O3 formation was highly NOx‐sensitive in air masses traveling from the southern part of the NCP but limited by anthropogenic hydrocarbons (especially alkenes) in air masses from the northern part of the NCP. The reduction of emissions from transportation and industry sectors would significantly reduce the regional O3 concentrations. Biomass burning also exerts a significant influence on regional O3 concentrations under certain circumstances. This study demonstrates that the regional background O3 at mountaintop levels is a good indicator of surface O3 pollution over a wide spatial coverage, and provides guidance for regional collaboration on emission control to mitigate photochemical air pollution over the NCP.

Quantification of Regional Ozone Pollution Characteristics and Its Temporal Evolution: Insights from Identification of the Impacts of Meteorological Conditions and Emissions

Ozone (O3) pollution has become the major new challenge after the suppression of PM2.5 to levels below the standard for the Pearl River Delta (PRD). O3 can be transported between nearby stations due to its longevity, leading stations with a similar concentration in a state of aggregation, which is an alleged regional issue. Investigations in such regional characteristics were rarely involved ever. In this study, the aggregation (reflected by the global Moran’s I index, GM), its temporal evolution, and the impacts from meteorological conditions and both local (i.e., produced within the PRD) and non-local (i.e., transported from outside the PRD) contributions were explored by spatial analysis and statistical modeling based on observation data. The results from 2007 to 2018 showed that the GM was positive overall, implying that the monitoring stations were surrounded by stations with similar ozone levels, especially during ozone seasons. State of aggregation was reinforced from 2007 to 2012, and remained stable thereafter. Further investigations revealed that GM values were independent of meteorological conditions, while closely related to local and non-local contributions, and its temporal variations were driven only by local contributions. Then, the correlation (R2) between O3 and meteorology was identified. Result demonstrated that the westerly belonged to temperature (T) and surface solar radiation (SSR) sensitive regions and the correlation between ozone and the two became intense with time. Relative humidity (RH) showed a negative correlation with ozone in most areas and periods, whereas correlations with u and v were positive for northerly winds and negative for southerly winds. Two important key points of such investigation are that, firstly, we defined the features of ozone pollution by characterizing the temporal variations in spatial discrepancies among all stations, secondly, we highlighted the significance of subregional cooperation within the PRD and regional cooperation with external environmental organizations.

A win-win strategy for simultaneous air-quality benign and profitable emission reduction during chemical plant shutdown operations

Although the flaring system is designed for the safety operation in chemical plants, the intensive flaring will cause not only tremendous raw material loss, but also large amounts of VOCs and NOx, which could escalate regional ozone formation and elevation under the solar radiation. Thus, it will be a win-win situation to preform air-quality conscious flare minimization (FM) for chemical plants, so that both environmental and industrial sustainability could be promoted. In this study, a systematic multi-scale methodology has been established to identify and demonstrate the win-win strategy for simultaneous air-quality benign and profitable emission reduction during chemical plant shutdown (CPS) operations. The major contribution of this study is that process-level dynamic simulations via Aspen Plus Dynamics have been seamlessly integrated with the regional-level air-quality modeling via CAMx to simultaneously accomplish both flare source savings and ozone impact minimization during the CPS operation. Case studies have indicated that the base case of CPS without FM could have a serious effect on the air-quality (1.6 ppb 8-h ozone observed). However, the improved case of CPS based on FM would significantly reduce such an ozone impact (only 0.1 ppb 8-h ozone observed); meanwhile the flare source and CO2 emission reductions, as well as the plant economic savings are respectively 165.2 tons, 479.1 tons, and US$133,945.6.

Ozone Content over the Russian Federation in 2020

The review is based on the results of operation of the total ozone (TO) monitoring system in Russia and neighboring countries that functions in the operational mode at the Central Aerological Observatory. The monitoring system uses data from the national network equipped with M-124 filter ozonometers being under the methodological supervision of the Main Geophysical Observatory. The quality of the functioning of the entire system is operationally controlled using the OMI satellite equipment observations (NASA, USA). Basic TO observation data are generalized for each month of the fourth quarter of 2020, for the fourth quarter, and for the whole year. Data of routine observations of surface ozone in the Moscow region are also presented.

Data resource profile: the allergic disease database of the Korean National Health Insurance Service.

Researchers have been interested in probing how the environmental factors associated with allergic diseases affect the use of medical services. Considering this demand, we have constructed a database, named the Allergic Disease Database, based on the National Health Insurance Database (NHID). The NHID contains information on demographic and medical service utilization for approximately 99% of the Korean population. This study targeted 3 major allergic diseases, including allergic rhinitis, atopic dermatitis, and asthma. For the target diseases, our database provides daily medical service information, including the number of daily visits from 2013 and 2017, categorized by patients’ characteristics such as address, sex, age, and duration of residence. We provide additional information, including yearly population, a number of patients, and averaged geocoding coordinates by eup, myeon, and dong district code (the smallest-scale administrative units in Korea). This information enables researchers to analyze how daily changes in the environmental factors of allergic diseases (e.g., particulate matter, sulfur dioxide, and ozone) in certain regions would influence patients’ behavioral patterns of medical service utilization. Moreover, researchers can analyze long-term trends in allergic diseases and the health effects caused by environmental factors such as daily climate and pollution data. The advantages of this database are easy access to data, additional levels of geographic detail, time-efficient data-refining and processing, and a de-identification process that minimizes the exposure of identifiable personal information. All datasets included in the Allergic Disease Database can be downloaded by accessing the National Health Insurance Service data sharing webpage (https://nhiss.nhis.or.kr).

Ozone Pollution Trend in the Pearl River Delta Region During 2006-2019

Based on the monitoring data of the Guangdong-Hong Kong-Macao Pearl River Delta Regional (PRD) Air Quality Monitoring Network from 2006 to 2019, the ozone trend in RRD was analyzed using the Mann-Kendall test method, Sen's slope method, and the Pettitt change point test. The results show that:① the average ozone concentration in the PRD has increased significantly from 2006 to 2019 (P<0.05), with an average growth rate of 0.80 μg·(m3·a)-1. After 2016, the rate of ozone increase has accelerated. ② The average annual ozone concentration in the central PRD increased significantly, while in the peripheral areas of the PRD, this is not obvious. Ozone increases significantly in summer but not in other seasons.③ From 2006 to 2019, the concentration of NO2 in the central PRD decreased remarkably, so the titration effect weakened and resulted in an increase in the ozone concentration. The concentration of NO2 in the marginal areas of the PRD has little change, so the ozone concentration in these areas has little change. ④ With the changes of VOCs and NO2 concentrations, the chemical sensitivity of O3 production in the PRD is changing. The VOC-limited regimes are continuously decreasing, and the mixed NOx-VOC-limited regimes and NOx-limited regimes are increasing. In order to deal with regional ozone pollution, the cooperative control of VOCs and NOx needs to strengthen.

Ozone Content over the Russian Federation in 2020

The review is based on the results of operation of the total ozone (TO) monitoring system in Russia and neighboring countries that functions in the operational mode at the Central Aerological Observatory. The monitoring system uses data from the national network equipped with M-124 filter ozonometers being under the methodological supervision of the Main Geophysical Observatory. The quality of the functioning of the entire system is operationally controlled using the OMI satellite equipment observations (NASA, USA). Basic TO observation data are generalized for each month of the fourth quarter of 2020, for the fourth quarter, and for the whole year. Data of routine observations of surface ozone in the Moscow region are also presented.

Diurnal and inter-annual variability of surface ozone in Baicheng region, China

With the rapid development of industry and economy, the problem of ozone (O3) pollution in China is of increasing concern in recent years. The problem of ozone pollution has become worse in Baicheng City which belongs to the province of Jilin. We analyze the spatial and temporal distribution of surface ozone and its correlation with precursors and meteorological factors during 2015 and 2019 using data from the automatic Atmospheric Environmental Quality Monitoring Station located in Baicheng. Results showed that the daily and monthly mean values of O3 concentration were both single-peak patterns, and interannual variation presented a inverted ‘V’ pattern in Baicheng. The high concentration of O3 in a year generally occurs from May to July, with the highest daily concentration occurring in the afternoon. The total number of days with O3 concentration exceeding the limits was 35 days from 2015 to 2019, among which the number of days exceeding the maximal daily average eight-hour (MDA8) O3 of 100 μg/m3 was the highest in 2018, and the 90th percentile MDA8 showed an overall growth pattern. Seasonal variations in O3 concentration in 2018 and 2019 were not consistent with the three previous years.

Analysis of the Spatial and Temporal Variation Characteristics of Ozone in the Pearl River Delta Region from 2016 to 2020

Based on the historical data of air ozone monitoring of Pearl River Delta from 2016 to 2020, the temporal and spatial variation characteristics of ozone in the Pearl River Delta were analyzed. The results showed that the mean change curves of Q3 in the seven cities in the Pearl River Delta region from 2016 to 2020 were M-shaped, and the change trend was basically the same, except Huizhou and Zhuhai. The over standard rate of daily mean value of Q3 in Jiangmen City from 2016 to 2020 was more than 10%, and the over standard situation of daily mean value of Q3 was serious. In the Pearl River Delta region, the change trend of the monthly mean value of Q3 in the same year was basically the same. On the whole, the mean value from August to November was higher, and the mean value in June was lower. The peak of Q3 concentration appeared between 12:00 and 16:00 in the daytime, and it was generally low at night.

An unusual high ozone event over the North and Northeast China during the record-breaking summer in 2018

Under the background of global warming, the summer temperature of the North and Northeast China (NNEC) has significantly increased since 2017, which was accompanied by the aggravated ozone (O3) pollution. In 2018, the NNEC experienced a record-breaking summer of the past 40 years. Influenced by the abnormal high temperatures, a regional ozone event occurred on 2-3 August, over 63% of 79 selected cities in the NNEC were exposed to O3 pollution, and the maximum value of MDA8 O3 reached 268 μg/m3. Observations indicated that ozone concentrations agree well with the maximum temperature at 2 meters (MT2M) over NNEC with a correlation coefficient of 0.69. During the pollution episode, strong downdraft in the local high (35°N-42.5°N, 112.5°E-132.5°E; LH) over the NNEC created the favourable meteorological conditions for O3 formation. By analyzing the horizontal wind and wave activity fluxes (WAFs) at 200 hPa, we found that the LH formation was resulted from the Rossby wave propagation from upstream along the mid-latitude Asian jet. The split polar vortex intrusion further strengthened the amplitude of the Rossby wave and reinforced the LH. Moreover, a secondary circulation between Typhoon Jongdari and the LH contributed to the enhanced LH with strong subsidence. On the other hand, the stratospheric intrusions under the deep subsidence also contributed to the enhanced surface O3. In this study, the deep-seated meteorological dynamical mechanisms contributing to the abnormal high temperatures were investigated, which can lead to a better understanding of the regional O3 pollution over NNEC under the global-warming background.

The interaction of ozone and aerosol in a semi-arid region in the Middle East: Ozone formation and radiative forcing implications

Investigations on the variations in ozone concentration, aerosol properties, and ozone-aerosol interactions can help to better understand the atmospheric radiation budget and their effects on climate. In this study, the interaction of ozone and aerosol was analyzed over Zanjan, Iran. The seasonal cycle of total column ozone demonstrated that high ozone concentrations often occur in early spring and winter. However, the seasonal cycle of tropospheric ozone showed that high concentrations of tropospheric ozone often happen in the spring and summer. The high values of Aerosol Optical Depth (AOD), Particulate Matter (PM10) and Absorption Aerosol Optical Depth (AAOD) were observed in the spring and summer, whereas low values in the fall and winter. The results showed that tropospheric ozone and AOD were negatively correlated during the spring and summer seasons. Especially on dusty days, the aerosol has reduced the concentration of ozone in the atmosphere. The correlation coefficients between PM10 and ozone were negative during dusty days/months. Moreover, the relation of ozone with a fine mode fraction of AOD depicted negative correlations in the spring and summer and positive correlation in the fall and winter. A comprehensive study on the effects of the aerosol types on ozone concentration showed that anthropogenic fine mode aerosols such as urban/industrial had a positive impact on ozone production, contrary to the effect of dust, which reduced ozone. This study showed that coarse mode aerosols such as dust with higher AOD, reduced the sunlight to reach the earth's surface. As a result, aerosol radiative forcing (ARF) values were found to be more negative at the surface; thus, the photolysis rate decreased considerably, and the concentration of surface ozone was reduced significantly.

Quadrennial variability and trends of surface ozone across China during 2015–2018: A regional approach

China has undergone headlong economic development, yielding a secondary air pollutant ‘ozone’, which has stirred up worldwide concerns. This study evaluates quadrennial, and seasonal surface ozone variations, ozone trends along with its significance through seasonal and deseasonal datasets, and ozone-NO2 correlation to codify a precedent for pollution control policies. China is divided into eight regions namely: Northeast (NE), Northwest (NW), North (N), East (E), Central (C), South (S), Southwest (SW), and Tibet (T), to exploit four-years data via (a) ozone 8-hr moving averages (O3-8hr), (b) hourly ozone monthly mean (O3-MM), (c) hourly ozone daily maximum MM (O3-DM-MM), (d) mean of the daily maximum 8-hr average ozone (MDA8-O3), (e) hourly ozone averages (O3-1hr), and (f) hourly NO2 averages (NO2-1hr), respectively. Quadrennial variations show distinct regions (i) Northeast with daily upraised value of 164.59 μg/m3, (ii) North possessing increased monthly variation of 125 μg/m3, and (iii) Tibet containing maximum yearly value of 79.81 μg/m3, respectively. Seasonal variations outpace North and South regions. The highest and lowest values of seasonal variations in North region are 135.61 μg/m3, and 23.96 μg/m3 during summer and winter, while maximum values of South region are 87.98 μg/m3 in autumn. In trend analysis, the seasonal dataset highlights higher ozone values during autumn, i.e. 74.12 μg/m3 and 141.96 μg/m3 for South and Central regions, respectively. In the meantime, the deseasonal dataset reveals the presence of increasing ozone trends in all studied regions. In assessing statistical significance by Mann-Kendall test, seasonal dataset rolls out statistically insignificant trends with an exception of South region. Meanwhile, deseasonal dataset projects statistically significant trends in all the eight regions. Lastly, two continual regions North and South are selected to determine ozone-NO2 relationship. The multiple analytical approaches unveil that O3 has increased by 20.86%, 14.05% and 12.64% in North, Central and South regions. The dissimilar climate, land cover modifications, precursors transportation and vehicular emissions might be some of the rationales to give rise to regional ozone variations. Therefore, we suggest revamping of emissions control policies and their precise implementation to abate ozone pollution.

Effects of global ship emissions on European air pollution levels

Abstract. Ship emissions constitute a large, and so far poorly regulated, source of air pollution. Emissions are mainly clustered along major ship routes both in open seas and close to densely populated shorelines. Major air pollutants emitted include sulfur dioxide, NOx, and primary particles. Sulfur and NOx are both major contributors to the formation of secondary fine particles (PM2.5) and to acidification and eutrophication. In addition, NOx is a major precursor for ground-level ozone. In this paper, we quantify the contributions from international shipping to European air pollution levels and depositions. This study is based on global and regional model calculations. The model runs are made with meteorology and emission data representative of the year 2017 after the tightening of the SECA (sulfur emission control area) regulations in 2015 but before the global sulfur cap that came into force in 2020. The ship emissions have been derived using ship positioning data. We have also made model runs reducing sulfur emissions by 80 % corresponding to the 2020 requirements. This study is based on model sensitivity studies perturbing emissions from different sea areas: the northern European SECA in the North Sea and the Baltic Sea, the Mediterranean Sea and the Black Sea, the Atlantic Ocean close to Europe, shipping in the rest of the world, and finally all global ship emissions together. Sensitivity studies have also been made setting lower bounds on the effects of ship plumes on ozone formation. Both global- and regional-scale calculations show that for PM2.5 and depositions of oxidised nitrogen and sulfur, the effects of ship emissions are much larger when emissions occur close to the shore than at open seas. In many coastal countries, calculations show that shipping is responsible for 10 % or more of the controllable PM2.5 concentrations and depositions of oxidised nitrogen and sulfur. With few exceptions, the results from the global and regional calculations are similar. Our calculations show that substantial reductions in the contributions from ship emissions to PM2.5 concentrations and to depositions of sulfur can be expected in European coastal regions as a result of the implementation of a 0.5 % worldwide limit of the sulfur content in marine fuels from 2020. For countries bordering the North Sea and Baltic Sea SECA, low sulfur emissions have already resulted in marked reductions in PM2.5 from shipping before 2020. For ozone, the lifetime in the atmosphere is much longer than for PM2.5, and the potential for ozone formation is much larger in otherwise pristine environments. We calculate considerable contributions from open sea shipping. As a result, we find that the largest contributions to ozone in several regions and countries in Europe are from sea areas well outside European waters.

Daily spatiotemporal prediction of surface ozone at the national level in China: An improvement of CAMS ozone product

Accurate nationwide spatiotemporal distribution of ambient ozone product is critical for environment & health departments and for researches to investigate the influence of ozone for epidemiological studies. Our hybrid method, the novel CAMS (The Copernicus Atmosphere Monitoring Service) ozone improvement (CAO3_I) method, is the first attempt to predict ambient ozone by improving CAMS ozone (CAO3) products. For this novel framework, the SVM (Support Vector Machine) has been adopted for classification through the most significant regional ozone patterns which were extracted through the REOF (Rotated Empirical Orthogonal Function) technique. For each classified region, meteorological data, geographical data, CAMS ozone and ground-sites ozone are fed into random forest for regional regulation training and prediction. The CAO3_I method has shown its great feasibility in daily ozone surface distribution prediction. Based on daily averaged ozone concentrations for each station (STO3), the performance of CAO3 products (R2 = 0.35, RMSE = 25.77 μg/m3, MAPE = 42.06) have significantly improved to CAO3_I (R2 = 0.81, RMSE = 14.10 μg/m3, MAPE = 22.37), which shows above 97.4% R2 and RMSE have been improved. Our model is also capable to predict high level ozone concentrations in summer where the R2 has improved from 0.37 (for CAO3) to 0.81. In comparison with ground monitoring stations, the CAMS ozone improvement results can excellently reflect the distribution of daily ground-level ozone concentration and outperform previous statistical models in predicting ambient O3 concentrations. Therefore, the prediction results and our proposed model can be used for future epidemiological studies and air pollution controlling programs.

Global nitrous acid emissions and levels of regional oxidants enhanced by wildfires

Nitrous acid (HONO) is a precursor of the hydroxyl radical in the atmosphere, which controls the degradation of greenhouse gases, contributes to photochemical smog and ozone production, and influences air quality. Although biomass burning is known to contribute substantially to global aerosols and reactive gas emissions, pyrogenic contributions to HONO emissions are poorly constrained and often omitted in models. Here we present a global survey of TROPOMI/Sentinel-5 Precursor satellite sounder observations and show that HONO emissions are consistently enhanced in fresh wildfire plumes. Comparing major ecosystems (savanna, grassland, shrubland and tropical and extratropical forests), we found that the enhancement ratios of HONO to nitrogen dioxide varied systematically with biome type, with the lowest in savannas and grasslands and highest in extratropical evergreen forests. Supported by airborne measurements, we demonstrate that previous assessments underestimate pyrogenic HONO emissions by a factor of 2–4 across all ecosystem types. We estimate that HONO emissions are responsible for two-thirds of the hydroxyl radical production in fresh wildfire plumes worldwide and act to accelerate oxidative plume chemistry and ozone production. Our findings suggest that pyrogenic HONO emissions have a substantial impact on atmospheric composition, which enhances regional ozone levels by up to 7 ppbv. Satellite observations reveal that fresh wildfire plumes are a globally important source of nitrous acid, enhancing oxidative plume chemistry and regional ozone levels.

Effect of deep convection on the tropical tropopause layer composition over the southwest Indian Ocean during austral summer

Abstract. Balloon-borne measurements of cryogenic frost-point hygrometer (CFH) water vapor, ozone and temperature and water vapor lidar measurements from the Maïdo Observatory on Réunion Island in the southwest Indian Ocean (SWIO) were used to study tropical cyclones' influence on tropical tropopause layer (TTL) composition. The balloon launches were specifically planned using a Lagrangian model and Meteosat-7 infrared images to sample the convective outflow from tropical storm (TS) Corentin on 25 January 2016 and tropical cyclone (TC) Enawo on 3 March 2017. Comparing the CFH profile to Aura's Microwave Limb Sounder's (MLS) monthly climatologies, water vapor anomalies were identified. Positive anomalies of water vapor and temperature, and negative anomalies of ozone between 12 and 15 km in altitude (247 to 121 hPa), originated from convectively active regions of TS Corentin and TC Enawo 1 d before the planned balloon launches according to the Lagrangian trajectories. Near the tropopause region, air masses on 25 January 2016 were anomalously dry around 100 hPa and were traced back to TS Corentin's active convective region where cirrus clouds and deep convective clouds may have dried the layer. An anomalously wet layer around 68 hPa was traced back to the southeast Indian Ocean where a monthly water vapor anomaly of 0.5 ppmv was observed. In contrast, no water vapor anomaly was found near or above the tropopause region on 3 March 2017 over Maïdo as the tropopause region was not downwind of TC Enawo. This study compares and contrasts the impact of two tropical cyclones on the humidification of the TTL over the SWIO. It also demonstrates the need for accurate balloon-borne measurements of water vapor, ozone and aerosols in regions where TTL in situ observations are sparse.

An Optimization Approach for Hourly Ozone Simulation: A Case Study in Chongqing, China

Continuous spatial knowledge is required to control the regional ozone pollution. Measurements from ground-level sites are beneficial to this goal, but their number is limited due to the huge expenses of site establishment, operation, and maintenance. Remote sensing seems a promising data source, but its application is challenged by bad weather conditions. Always covered by thick clouds, Chongqing, a populated industrial city in west China, is facing serious ozone pollution, but relevant studies here are relatively insufficient. Another alternative is estimating ozone by models. Well-performed models degrade in Chongqing partially due to the very complex terrain. Modeled hourly ozone does not agree with ground-level measurements. Therefore, an optimization approach is proposed to improve model estimates for such regions. This approach integrates the ground-level information (e.g., measured ozone and meteorology) through the employment of ResNet (Residual Network). ResNet overcomes the notorious vanishing gradient issue in classic neural networks, and the ability of learning complex systems is largely boosted. Ozone distribution is like a gray image that varies every second, which is not the case usually learned by ResNet. A color-image alike data structure is raised to address this &#x201C;nonstill image&#x201D; problem; according to the Taylor Expansion, polynomials can describe a complex system, and the errors are acceptable. To facilitate the usage in business operations, this approach is designed to be robust, inexpensive, and easy to use. The scheme of control site selection is discussed in detail. In cross-validations, this approach performs well, averaged <inline-formula> <tex-math notation="LaTeX">$R^{2}$ </tex-math></inline-formula> is higher than 0.9 and the error is less than <inline-formula> <tex-math notation="LaTeX">$5 ~\mu \text {g/m}^{3}$ </tex-math></inline-formula>.