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The Yangtze River Delta (YRD) region locates on the eastern coast of China, and it has suffered severe O 3 pollutions due to high and mixed emissions of air pollutants. There are 3 different emission sectors for O 3 precursors in the region, including anthropogenic VOC S and NO X emissions, ship emissions (mainly NO X), and biogenic emissions from a large forest (biogenic VOC S). This unique emission mixture produces complicated chemical processes in studying the O 3 pollutions in the region. This study aims to identify the contribution of the ship emissions to O 3 pollutions, as well as the effect of mixing emissions on O 3 pollutions in YRD. To identify the individual emission effect, the WRF-Chem model is used in this study. The model generally performs well in simulating meteorological parameters and air pollutants against observations in YRD. Sensitive study suggests that the ship emissions have important effects on the O 3 concentrations over ocean and inland, with a maximum increase of 30–50 μg m−3 occurred mainly in the ship track regions. However, the ship emissions have a very complicated effect on the in-land O 3 concentrations. In the north of Shanghai, the NO X concentrations are high due to high anthropogenic emissions, and a further increase in NO X emissions from ship results in depressing O 3 chemical production. In contrast, in the south of Shanghai, there are high biogenic VOC emissions (mainly isoprene) and low NOx concentrations. As a result, the O 3 concentrations are enhanced by 30–50 μg m−3, due to the mixing between ship and forest emissions. This study suggests that ship emissions play important roles in controlling O 3 pollutions in YRD. Furthermore, the mixing emissions between ship, anthropogenic, and biogenic emissions in YRD produce a complicated O 3 chemical production and need to be carefully considered in controlling strategy of O 3 pollution in the region. Unlabelled Image • The effect of ship emission in YRD on O 3 formation • Complex mixing emissions among the ship, anthropogenic, and biogenic emissions in YRD • The mixing between ship and anthropogenic emissions could depress O 3 in northern YRD. • The mixing between ship and biogenic emissions could enhance O 3 in southern YRD. [ABSTRACT FROM AUTHOR]

Abstract The focus of this study is to evaluate the impact of biomass burning (BB) from South Asia and Southeast Asia on the glaciers over the Tibetan Plateau. The seasonality and long-term trend of biomass fires measured by Terra and Aqua satellite data from 2010 to 2016 are used in this study. The analysis shows that the biomass burnings were widely dispersed in the continental of Indian and Southeast Asia and existed a strong seasonal variation. The biomass burnings in winter (January) were relatively weak and scattered and were significantly enhanced in spring (April). The highest biomass burnings located in two regions. One was along the foothill of Himalayas, where is a dense population area, and the second located in Southeast Asia. Because these two high biomass burning regions are close to the Tibetan Plateau, they could have important effects on the BC deposition over the glaciers of the Tibetan Plateau. In order to study the effect of BB emissions on the deposition over the glaciers in the Tibetan Plateau, a regional chemical model (WRF-Chem; Weather Research and Forecasting Chemical model) was applied to simulate the BC distributions and the transport from BB emission regions to the glaciers in Tibetan Plateau. The result shows that in winter (January), due to the relatively weak BB emissions, the effect of BB emissions on BC concentrations was not significant. The BC concentrations resulted from BB emissions ranged from 0.1 to 2.0 μg/m3, with high concentrations distributed along the foothill of Himalayas and the southeastern Asia region. Due to the relative low BC concentrations, there was insignificant effect of BB emissions on the deposition over the glaciers in the Tibetan Plateau in winter. However, the BB emissions were highest in spring (April), producing high BC concentrations. For example, along the Himalayas Mountain and in the southeastern Asia region, The BC concentrations ranged from 2.0 to 6.0 μg/m3. In addition to the high BC concentrations, there were also west and south prevailing winds in these regions. As a result, the BC particles were transported to the glaciers in the Tibetan Plateau, causing significant deposition of BC particles on the snow surface of the glaciers. This study suggests that the biomass burning emissions have important effects on the BC deposition over the glaciers in the Tibetan Plateau, and the contaminations of glaciers could have significant impact on the melting of snow in the Tibetan Plateau, causing some severe environmental problems, such as the water resources. Graphical abstract Unlabelled Image Highlights • Biomass fires in South Asia measured by Terra and Aqua satellite data from 2010 to 2016 are analyzed. • The highest biomass burnings located in two regions (along the foothill of Himalayas and Southeastern Asia) • Biomass burning emissions were highest in spring, producing high BC concentrations (2.0 to 6.0 μg/m3) • BC particles were transported to the glaciers in TP, causing significant deposition on the snow surface of the glaciers [ABSTRACT FROM AUTHOR]

In recent years, ozone (O 3 ) is often the major pollutant during summertime in China. In order to better understand this problem, a long-term measurement of ozone (from 2006 to 2015) and its precursors (NO x and VOCs) as well as the photochemical parameter (UV radiation) in a mega city of China (Shanghai) is analyzed. The focus of this study is to investigate the trend of O 3 and the causes of the O 3 trend in large cities in China. In order to understand the relationship between the O 3 precursors and O 3 formation, two distinguished different sites of measurements are selected in the study, including an urbanization site (XJH-Xujiahui) and a remote site (DT-Dongtan). At the XJH site, there are high local emissions of ozone precursors (such as VOCs and NO x ), which is suitable to study the effect of O 3 precursors on O 3 formation. In contrast, at the DT site, where there are low local emissions, the measured result can be used to analyze the background conditions nearby the city of Shanghai. The analysis shows that there were long-term trends of O 3 and NO x concentrations at the urban site (XJH) from 2006 to 2015 (O 3 increasing 67% and NO x decreasing 38%), while there were very small trends of O 3 and NO x concentrations at the background site (DT). The analysis for causing the O 3 trend suggests that (1) the large O 3 increase at the urban area (XJH) was not due to the regional transport of O 3 ; (2) the measurement of solar radiation had not significant trend during the period, and was not the major cause for the long-term O 3 trend; (3) the measurement of VOCs had small change during the same period, suggesting that the trend in NO x concentrations at the urban site (XJH) was a major factor for causing the long-term change of O 3 at the urban area of Shanghai. As a result, the O 3 and NO x concentrations from 2006 to 2015 at the urban area of Shanghai were strongly anti-correlated, suggesting that the extremely high NO x concentration in the urban area depressed the O 3 concentrations. It is interesting to note that the anti-correlation between O 3 and NO x was in an un-linearly relationship. Under high O 3 concentration condition, the ratio of Δ[O 3 ]/Δ[NO x ] was as large as − 1.5. In contrast, under low O 3 concentrations, the ratio of Δ[O 3 ]/Δ[NO x ] was only − 0.2. This result suggested that when O 3 concentration was high, it was more sensitive to NO x concentration, while when O 3 concentration was low, it was less sensitive to NO x concentration. This study provides useful insights for better understanding the causes of the long-term-trend of regional O 3 pollution nearby Shanghai, and has important implication for air pollution control in large cities in China. Due to the fact that NO x and VOCs are not only precursors for O 3 , but also are important precursors for particular matter (PM). If reduction of NO x leads to decrease in PM, but increase in O 3 , the NO x emission control become a very complicated issue and need to carefully design a comprehensive control method. [ABSTRACT FROM AUTHOR]

The Tibetan Plateau (TP) plays important roles in global climate and environment. This study combines in-situ BC measurements in the Himalayas and the Indo-Gangetic Plain (IGP) with a regional dynamical and chemical model (WRF-Chem model) to investigate the effect of the trans-Himalayas on black carbon (BC) from the IGP to the TP during Indian summer monsoon. To determine topographic effects of the trans-Himalayas on BC concentrations over the TP, sensitive experiments were conducted by applying the WRF-Chem model. The results showed that the reduction of the altitude of the Himalayas had an important effect on the trans-Himalayas transport of BC. There was an obvious increase in BC concentration over the trans-Himalayas region, but no significant increase over the TP because the TP (a.m.s.l ~ 4 km) always acted as a wall to prevent BC transport from the IGP to the TP. The trans-Himalayas transport of BC was strongly dependent upon meteorological conditions over the IGP. During summer monsoon, there were three types of cyclones at different locations and one kind of convergent circulation in the IGP. Under the condition of convergent airflows, a strong northeastward wind produced the trans-Himalayas transport of BC. As a result, BC concentrations in the southeastern TP significantly increased to 0.6–0.8 μg m − 3 . When the cyclone located in the eastern IGP, high BC concentrations over the IGP were transported along the foothill of the Himalayas, resulting in a significant reduction of the trans-Himalayas transport. When the cyclone moved to the west, the dynamical perturbations for the trans-Himalayas transport were weaker than the eastern cyclone, and the trans-Himalayas transport were enhanced in the middle and eastern Himalayas. This study will be helpful to assess the impacts of BC particles emitted from South Asia on regional climate change and ecological environment over the TP in the future. [ABSTRACT FROM AUTHOR]

Beijing, the capital of China, is a mega city with a population of > 20 million. In recent years, the city has experienced heavy air pollution, with particulate matter (PM) being one of its top pollutants. In the last decade, extensive efforts have been made to characterize the sources, properties, and processes of PM in Beijing. Despite progress made by previous studies, there are still some important questions to be answered and addressed. The focus of this research is to study the impact of the heterogeneous hydrolysis of N 2 O 5 on the formation of nitrate (NO 3 − ) and ammonium (NH 4 + ) in Beijing. The results show that during heavy pollution days (e.g., during 14–17 September 2015, with PM 2.5 concentration over 100 μg/m 3 ), the concentrations of NO 2 and O 3 were high, with maxima of 90 and 240 μg/m 3 , respectively, providing high precursors for the formation of N 2 O 5 . In addition, the aerosol and sulfate concentrations were also high, with maxima of 201 μg/m 3 and 23 μg/m 3 respectively, providing reacting surface for the heterogeneous reaction. As a result, the hydrolysis of N 2 O 5 led to 21.0% enhancement of nitrate (NO 3 − ) and 7.5% enhancement of ammonium (NH 4 + ). It is worth to note that this important effect only occurred in high pollution days (PM 2.5 concentration over 100 μg/m 3 ). During low-pollution periods (PM 2.5 concentration < 100 μg/m 3 ), the effect of hydrolysis of N 2 O 5 on the formation of nitrate and ammonium was insignificant (variation rate < 5%). This study suggests that during heavy pollution periods, the hydrolysis of N 2 O 5 enhances the level of aerosol pollution in Beijing, and needs to be further studied in order to perform efficient air pollution control and mitigation strategies. [ABSTRACT FROM AUTHOR]

Summertime ozone (O 3) pollution has frequently occurred in the Beijing – Tianjin – Hebei (BTH) region, China, since 2013, resulting in detrimental impacts on human health and ecosystems. The contribution of weather shifts to O 3 concentration variability owing to climate change remains elusive. By combining regional air chemistry model simulations with near-surface observations, we found that anthropogenic emission changes contributed to approximately 23% of the increase in maximum daily 8-h average O 3 concentrations in the BTH region in June – July – August (JJA) 2017 (compared with that in 2013). With respect to the weather shift influence, the frequencies, durations, and magnitudes of O 3 exceedance were consistent with those of the heat wave events in the BTH region during JJA in 2013 – 2017. Intensified heat waves are a significant driver for worsening O 3 pollution. In particular, the prolonged duration of heat waves creates consecutive adverse weather conditions that cause O 3 accumulation and severe O 3 pollution. Our results suggest that the variability in extreme summer heat is closely related to the occurrence of high O 3 concentrations, which is a significant driver of deteriorating O 3 pollution. [Display omitted] • Anthropogenic emission changes enhanced MAD8 [O 3 ] by 23% from 2013 to 2017. • Increasing O 3 exceedances are related to the intensified heat waves. • Persistent O 3 pollution events increased during JJA 2017 compared with those in 2013. • Prolonged durations of heat wave events significantly contribute to O 3 increases. [ABSTRACT FROM AUTHOR]

We conducted a year-long WRF-Chem (Weather Research and Forecasting Chemical) model simulation of elemental carbon (EC) aerosol and compared the modeling results to the surface EC measurements in the Guanzhong (GZ) Basin of China. The main goals of this study were to quantify the individual contributions of different EC sources to EC pollution, and to find the major cause of the EC pollution in this region. The EC measurements were simultaneously conducted at 10 urban, rural, and background sites over the GZ Basin from May 2013 to April 2014, and provided a good base against which to evaluate model simulation. The model evaluation showed that the calculated annual mean EC concentration was 5.1 μgC m −3 , which was consistent with the observed value of 5.3 μgC m −3 . Moreover, the model result also reproduced the magnitude of measured EC in all seasons (regression slope = 0.98–1.03), as well as the spatial and temporal variations (r = 0.55–0.78). We conducted several sensitivity studies to quantify the individual contributions of EC sources to EC pollution. The sensitivity simulations showed that the local and outside sources contributed about 60% and 40% to the annual mean EC concentration, respectively, implying that local sources were the major EC pollution contributors in the GZ Basin. Among the local sources, residential sources contributed the most, followed by industry and transportation sources. A further analysis suggested that a 50% reduction of industry or transportation emissions only caused a 6% decrease in the annual mean EC concentration, while a 50% reduction of residential emissions reduced the winter surface EC concentration by up to 25%. In respect to the serious air pollution problems (including EC pollution) in the GZ Basin, our findings can provide an insightful view on local air pollution control strategies. [ABSTRACT FROM AUTHOR]

In-situ measurement of black carbon (BC) concentration from September 2003 to August 2007 in the Xi'an City at the Guanzhong Basin located in the mid-western China (the Guanzhong Basin) was analyzed. A regional dynamics and aerosol model (WRF-Chem) was used to quantify the impacts of local emission, meteorological conditions, and regional atmospheric transport on seasonal variation of BC concentration at the Guanzhong Basin. The results show that the regional prevailing winds at the Guanzhong Basin were unfavorable for the horizontal transport. The mean wind speeds ranged from 1.0 m/s to 1.9 m/s. During winter, the wind at the Guanzhong Basin was very weak (∼1.0 m/s). During spring and autumn, there was a wind convergent zone at the Guanzhong Basin, constraining the BC concentrations inside the Guanzhong Basin. As a result, the BC concentrations were persistently high at the Guanzhong Basin. In addition to the high background concentrations, there was a strong seasonal variation, with a maximum in winter (winter maximum) and a minimum in summer (summer minimum), with the maximum of the mean concentration of 30 μg m −3 in 2003–2004 winter, and the minimum of 5 μg m −3 in 2004 summer. The model sensitivity study shows that the seasonal variation of BC concentration was largely due to the seasonal variation of BC emission, especially during winter with the maximum of BC emission. A strong annual decrease trend of the BC concentration was found from 2004 to 2007. It is interesting to note that the decrease of the BC concentration only occurred in winter. For example, the winter maximum was 20 μg m −3 in 2003, and reduced to 11 μg m −3 in 2006, with about 50% decrease. In contrast, the summer minimum was 10 μg m −3 in 2004 and 9 μg m −3 in 2007, with only 10% decrease. This study suggests that the rapid decrease in the winter maximum was mainly due to the reduction of the BC emission in winter, implying the effective winter emission control at the Guanzhong Basin. [ABSTRACT FROM AUTHOR]

The Xi'an City and the surrounding area (the Guan-Zhong—GZ region) in western China have been suffering severe air pollutions during wintertime in recent years. In-situ black carbon (BC) measurement combined with a regional dynamical and chemical model (WRF-Chem model) is used to investigate the formation of a haze episode occurred from Jan. 3rd to Jan. 13th 2013. The results show that the measured BC concentrations exhibit a large day-to-day variability. The impacts of synoptic weather systems, local meteorological parameters and mountain effect on the BC variability are studied. Because the GZ region is surrounded by two major mountains, the Loess Plateau in the north and the Qinling Mountains in the south, especially the peak of the Qinling Mountains higher than 3000 m, we particularly analyze the effects of the Qinling Mountains on the BC pollution. The analysis shows that the BC pollution in Xi'an City and the GZ region is strongly affected by the synoptic weather systems, local meteorological winds and the Qinling Mountains. Under a typical northeast wind condition, winds are blocked by the Qinling Mountains, and BC particles are trapped at the foothill of the mountains, resulting in high BC concentrations in the city of Xi'an. Under a typical east wind condition, BC particles are transported along a river valley and the foothill of the Qinling Mountains. In this case, the mountain-river valley plays a role to accelerate the east wind, resulting in a reduction of the BC pollution. Under a typical calm wind condition, the BC particles are less diffused from their source region, and there is a mountain breeze from the Qinling Mountains to the city of Xi'an, and BC particles accumulate in the city, especially in the north side of the city. This study illustrates that while locating between complicated terrain conditions, such as the GZ region, the mountains play very important roles for the formation of hazes in the region. [ABSTRACT FROM AUTHOR]

During recent winters, hazes often occurred in Beijing, causing major environmental problems. To understand the causes of this “Beijing Haze”, a haze episode (from Oct. 21 to Oct. 31, 2013) in Beijing was analyzed. During the episode, the daily mean concentration of fine particulate matter (PM 2.5 ) reached a peak value of 270 μg/m 3 on Oct. 28, 2013, and rapidly decreased to 50 μg/m 3 the next day (Oct. 29, 2013). This strong variability provided a good opportunity to study the causes of a “Beijing Haze”. Two numerical models were applied for this study. The first model is a chemical/dynamical regional model (WRF-Chem). This model is mainly used to study the effects that weather conditions have on PM 2.5 concentrations in the Beijing region. The results show that the presence of high air pressure in northwest Beijing (NW-High) generally produced strong northwest winds with clean upwind air. As a result, the NW-High played an important role in cleaning Beijing's PM. However, the NW-High's cleaning effect did not occur in every situation. When there was low air pressure in southeast Beijing (SE-Low) accompanied by an NW-High, an air convergent zone appeared in Beijing. The pollutants became sandwiched, producing high PM 2.5 concentrations in the Beijing region. The second model used in this study is a box model, which is applied to estimate some crucial parameters associated with the budget of PM 2.5 in the Beijing region. Under calm winds, the calculations show that continuous local emissions rapidly accumulate pollutants. The PM 2.5 concentrations reached 150 μg/m 3 and 250 μg/m 3 within one (1) day and two (2) days, respectively. Without horizontal dilution, this estimate can be considered as an upper time limit (the fastest time) for the occurrences of haze events in the Beijing region. The wind speed (WS b ) is calculated for the balance between the continuous emissions and atmospheric clean processes. The results show that the WS b is strongly dependent on the planetary boundary layer (PBL) height and the wind direction. Under SE-Low weather conditions, the WS b is 2 m/s with a higher PBL height (700 m). However, under lower PBL heights, the WS b rapidly increases, reaching 4.5 m/s and 7.0 m/s with PBL heights of 300 m and 200 m, respectively. In contrast, under NW-High weather conditions, the WS b reduces to 2.5 m/s and 4.0 m/s. These results suggest that when the prevailing wind in Beijing is a northwest wind (with wind speeds of >4 m/s), particulate matter (PM) begins to decrease. [ABSTRACT FROM AUTHOR]

Despite implementation of strict emission mitigation measures since 2013, heavy haze with high levels of secondary aerosols still frequently engulfs the Guanzhong Basin (GZB), China, during wintertime, remarkably impairing visibility and potentially causing severe health issues. Although the observed low ozone (O 3) concentrations do not facilitate the photochemical formation of secondary aerosols, the measured high nitrous acid (HONO) level provides an alternate pathway in the GZB. The impact of heterogeneous HONO sources on the wintertime particulate pollution and atmospheric oxidizing capability (AOC) is evaluated in the GZB. Simulations by the Weather Research and Forecast model coupled with Chemistry (WRF-Chem) reveal that the observed high levels of nitrate and secondary organic aerosols (SOA) are reproduced when both homogeneous and heterogeneous HONO sources are considered. The heterogeneous sources (HET-sources) contribute about 98% of the near-surface HONO concentration in the GZB, increasing the hydroxyl radical (OH) and O 3 concentration by 39.4% and 22.0%, respectively. The average contribution of the HET-sources to SOA, nitrate, ammonium, and sulfate in the GZB is 35.6%, 20.6%, 12.1%, and 6.0% during the particulate pollution episode, respectively, enhancing the mass concentration of fine particulate matters (PM 2.5) by around 12.2%. Our results suggest that decreasing HONO level or the AOC becomes an effective pathway to alleviate the wintertime particulate pollution in the GZB. [Display omitted] • High levels of secondary aerosols have been measured in winter in the Guanzhong Basin (GZB). • High HONO levels provide an alternative pathway for wintertime photochemistry. • Heterogeneous HONO deteriorates the wintertime particulate pollution in the GZB. • Heterogeneous HONO contributes about 12.2% to the wintertime PM 2.5 level in the GZB. • Heterogeneous HONO plays a more important role in the daytime PM 2.5 levels than nighttime. Capsule: The heterogeneous HONO sources deteriorate the wintertime particulate pollution in the Guanzhong Basin, with the PM 2.5 contribution of about 12.2%. [ABSTRACT FROM AUTHOR]

Abstract: A comprehensive measurement was carried out to analyze the heavy haze events during 2012–2013 winter in Beijing. The measured variables include some important meteorological parameters, such wind directions, wind speeds, relative humidity (RH), planetary boundary layer (PBL), solar radiation, and visibility. The aerosol composition and concentrations (including particular matters (PM2.5), nitrate (NO3), sulfate (SO4), ammonium (NH4)) as well as their gas-phase precursors (including nitrogen oxides (NO x ) and sulfur dioxide (SO2)) were analyzed during the period between Nov. 16, 2012 and Jan. 15, 2013. The results show that the hourly mean concentrations of PM2.5 often exceeded 200 μg/m3, with a maximum concentration of 600 μg/m3 on Jan. 13, 2013. The relative humidity was increased during the haze events, indicating that both aerosol concentrations and RH had important effect on the reduction of visibility, causing the occurrence of the haze events. Because the wind speeds were generally low (less than 1 m/s) during the haze event, the vertical dispersion and the PBL heights were very important factors for causing the strong variability of aerosol concentrations. This study also finds that under the lower visibility condition, the conversion from the gas-phase of NO x and SO2 to the particle phase of NO3 and SO4 were higher than the values under the higher visibility condition. Because the lower visibility condition was corresponding to the lower photochemical activity than the higher visibility condition, the higher conversion from gas phase to particle phase in the lower visibility condition indicated that there was important heterogeneous formation of NO3 and SO4 during the heavy haze events. [Copyright &y& Elsevier]

Abstract: Dust particles have important effects on solar radiation, climate, and photochemistry in the troposphere. Dust events were observed from March 16 to 20, 2006 in the Mexico City (MC) area during the MILAGRO (Megacity Initiative: Local and Global Research Observations) field experiment. In order to study the effects of dust aerosols on total aerosol mass concentrations and photochemistry, a regional chemical/dynamical model (Weather Research and Forecasting Chemical model version 3 – WRF/Chem-v3) was used in this study, and a dust module was implemented in the model. Analysis of model and observational data suggests that the large area of coastal dry lands to the northeast of MC is an important source of dust particles for the entire MC area. The simulations of both PM2.5 (total particle mass with radius less than 2.5 μm) and PM10 (total particle mass with radius less than 10 μm) concentrations are more consistent with observations than the results of the model without the dust module. During this dust period (March 16–20, 2006), the simulated dust aerosol mass accounts for about 70% of the total PM10 aerosol mass concentrations, with a strong diurnal variation. The results also suggest that dust aerosols have important effects on actinic fluxes and therefore photochemistry, especially on hydroxyl radical (OH) and ozone (O3) concentrations, in the MC area and the surrounding region. The dust particles decrease the photochemical production of OH, with a maximum reduction of 60% in the dust source region (northeast of the MC area). Near the city area, the reduction of OH concentrations is about 5–20%. The strongest effects on O3 concentrations are near MC, where the maximum reduction of O3 is about 10 ppbv. In the dust source region, O3 concentrations are reduced by about 3–5 ppbv. [Copyright &y& Elsevier]

Abstract: Since 2005, Shanghai Meteorological Bureau (SMB) has established an observational network for measuring VOC, NO x , O3 and aerosols in the Shanghai region. In this study, a rapid O3 changes from Aug/02/2007 to Aug/11/2007 was observed in the region. During this 10 day period, the noontime O3 maximum decreased from 100 to 130 ppbv to about 20–30 ppbv. In order to analyze the processes in controlling this rapid change of O3 during this short period, a newly developed regional chemical/dynamical model (WRF-Chem) is applied to study O3 variability in the Shanghai region. The model performances are evaluated by comparing the model calculation to the measurement. The result shows that the calculated magnitudes and diurnal variations of O3 are close to the measured results in city sites, but are underestimated at a rural petroleum industrial site, suggesting that the emissions from petroleum factories around this rural site are significantly underestimated and need to be improved. The calculated rapid changes of O3 concentrations, O3 precursors, and aerosols are consistent with the measured results, suggesting that the model is suitable to study the causes of this rapid O3 change. The model analysis indicates that weather conditions play important roles in controlling the surface O3 in the Shanghai region. During summer, there is a persistent sub-tropical high pressure system (SUBH) in southeast of Shanghai over Pacific Ocean. During the earlier time of the period (Aug/02–Aug/05), the SUBH system was weak, resulting in weak surface winds. With the calm winds, a noticeable noontime sea-breeze produced an inflow from ocean to land, generating a cycling pattern of wind directions. As a result, the high O3 concentrations were trapped in the Shanghai region, with a maximum concentration of 100–130 ppbv. By contrast, during the later time of the period (Aug/06–Aug/11), the SUBH was enhanced, resulting in strong surface winds. The high O3 concentrations formed in the city were rapidly transported to the downwind region of the city, resulting in low O3 concentrations in the Shanghai region. This study illustrates that the WRF-Chem model is a useful tool for studying the high variability of O3 concentrations in Shanghai, which has important implication for the prediction of high O3 concentration events in the city. [Copyright &y& Elsevier]

Soil nitrogen dioxide (NO X = NO 2 + NO) emissions have been measured and estimated to be the second most significant contributor to the NO X burden following the fossil fuel combustion source globally. NO X emissions from croplands are subject to being underestimated or overlooked in air pollution simulations of regional atmospheric chemistry models. With constraints of ground and space observations of NO 2 , the WRF-Chem model is used to investigate the cropland NO X emission and its contribution to the near-surface ozone (O 3) pollution in North China Plain (NCP) during a growing season as a case study. Model simulations have revealed that the cropland NO X emissions are underestimated by around 80% without constraints of satellite measured NO 2 column densities. The biogenic NO X source is estimated to account for half of the anthropogenic NO X emissions in the NCP during the growing season. Additionally, the cropland NO X source contributes around 5.0% of the maximum daily average 8h O 3 concentration and 27.7% of NO 2 concentration in the NCP. Our results suggest the agriculture NO X emission exerts non-negligible impacts on the summertime air quality and needs to be considered when designing emission abatement strategies. [Display omitted] • Cropland NO X emissions are underestimated by 80% without satellite constraints. • Biogenic NO X source accounts for half of the anthropogenic NO X emissions in the NCP. • Cropland NO X source contributes 5.0% of the MDA8 [O 3 ] and 27.7% of [NO 2 ] in the NCP. • Further reducing 50% cropland NO X leads to extra 5.2 μg m−3 decreases of MDA8 [O 3 ]. [ABSTRACT FROM AUTHOR]

Sensitivity of ozone (O3) concentrations in the Mexico City area to diurnal variations of surface air pollutant emissions is investigated using the WRF/Chem model. Our analysis shows that diurnal variations of nitrogen oxides (NO x =NO+NO2) and volatile organic compound (VOC) emissions play an important role in controlling the O3 concentrations in the Mexico City area. The contributions of NO x and VOC emissions to daytime O3 concentrations are very sensitive to the morning emissions of NO x and VOCs. Increase in morning NO x emissions leads to decrease in daytime O3 concentrations as well as the afternoon O3 maximum, while increase in morning VOC emissions tends to increase in O3 concentrations in late morning and early afternoon, indicating that O3 production in Mexico City is under VOC-limited regime. It is also found that the nighttime O3 is independent of VOCs, but is sensitive to NO x . The emissions of VOCs during other periods (early morning, evening, and night) have only small impacts on O3 concentrations, while the emissions of NO x have important impacts on O3 concentrations in the evening and the early morning. This study suggests that shifting emission pattern, while keeping the total emissions unchanged, has important impacts on air quality. For example, delaying the morning emission peak from 8 am to 10 am significantly reduced the morning peaks of NO x and VOCs, as well as the afternoon O3 maxima. It suggests that without reduction of total emission, the daytime O3 concentrations can be significantly reduced by changing the diurnal variations of the emissions of O3 precursors. [Copyright &y& Elsevier]

Recent studies show that the rapid increases in urbanization and human activities in the PRD region have important impacts on regional air quality. In addition to local anthropogenic emissions which are major driving forces for poor air quality in this region, biomass burning in Southeast Asia has also important contribution on aerosol and ozone concentrations in the PRD region. In this paper, this effect is analyzed by using satellite data, ground measurements and models. MODIS aerosol optical depth (AOD) distribution in March 2006 shows a clear enhancement in AOD between Southeast Asia and the PRD region. With detail wind analysis, two distinguished conditions are classified, i.e., Condition-1 (PRD is under influence of the biomass burning from Southeast Asia) and Condition-2 (PRD is not under influence of the biomass burning from Southeast Asia). The characterizations of aerosol, UV, and ozone in Guangzhou city (located in the PRD region) under these two conditions are analyzed. The analyses suggest that aerosols and CO concentrations are higher in Condition-1 than in Condition-2; while the UV intensity and O3 concentrations are lower in Condition-1 than in Condition-2. This result indicates that in Condition-1, the enhanced aerosol concentrations from the Southeast Asia biomass burning produce reduction of UV intensity, and thus decreases the formation of ozone in Guangzhou. [Copyright &y& Elsevier]

Shanghai Meteorological Bureau (SMB) has established a VOC laboratory and an observational station network for VOC, NO x and O3 measurements in the Shanghai region. The measurements became operational since 2005. In this study, we investigate spatial and temporal variability of O3 and its precursors (NO x and VOCs), and impacts of the precursors on O3 formation. A chemical mechanism model (NCAR-MM) is applied to assess the sensitivity of the O3 formation to NO x and VOC concentrations. The results show that O3 concentrations are higher in rural area than in center of the city, suggesting that there are O3 depression processes in center of city and air pollutant emissions are not favorable for the O3 chemical formation. The analysis suggests that the NO and NO2 concentrations in center of the city are lower during weekend than weekday due to less traffic and industrial activities. By contrast, the O3 concentrations are higher during weekend than weekday. During weekend, the reduction of NO2 leads to enhancement in OH radicals, resulting in the higher O3 production. This enhancement of weekend O3 is off-set by decrease in VOC concentrations. The chemical model study suggests that the decrease of NO x alone could result in a larger weekend O3 enhancement than the measured result. The model sensitivity study also suggests that O3 concentration decreases when NO x concentration is enhanced. Both model and measurement results indicate that the O3 formation is clearly under VOC-sensitive regime in the city of Shanghai. As a result, in the urban area, the O3 production is strongly depressed by high NO x concentrations, resulting in lower O3 concentration in center of the city than in rural area of the city. This study further shows that the highly reactive VOCs (aromatics) play important roles in determining the O3 formation. The ratio of toluene/benzene suggests that automobiles play important roles in the O3 formation in the city of Shanghai. Further increase in automobiles in Shanghai could lead to potential high O3 concentration in the future. [Copyright &y& Elsevier]

This paper suggests that the rapid increase in urbanization and human activities has important impacts on visibility in the Pearl River Delta (PRD) region. A long-term trend of visibility in Guangzhou (one of the largest cities in PRD) shows that between 1954 and 2006, there is a rapid change in visibility. Between 1954 and 1972, low visibility has the smallest occurrence (less than a few days per year). Between 1972 and 1980, the visibility condition is within a transition period, and the occurrence of low visibility increases rapidly. Between 1980 and 2006, the occurrence of low visibility remains very high (150daysyear−1), suggesting that the city of Guangzhou is often under low-visibility conditions since the 1980s. In order to understand the causes of the low visibility in Guangzhou, we analyze physical and chemical characterizations of a low-visibility event occurring between 15 and 29 November 2005. The analysis suggests that high concentration of aerosol particles is a major cause for the low visibility. The threshold aerosol concentration that is corresponding to the low visibility (<10km) is about 120μgm−3. Further analysis indicates that the relationship between aerosol concentrations and visibility appears in a non-linearity correlation. When aerosol concentrations are very high (above 120μgm−3), the change in visibility is not sensitive to aerosol concentration. By contrast, when aerosol concentrations are <120μgm−3, the change in visibility is very sensitive to aerosol concentrations. This study also shows that absorbing aerosol particles (such as element carbon (EC)) play important roles in the reduction of visibility. In most cases, the extremely low visibility (<2km) is often resulted from high EC concentrations (above 15μgm−3). In averaged condition, small scattering aerosol particles (<1μm in radius) have the largest contribution to the reduction of visibility (about 70%). By contrast, large scattering particles have the smallest contribution to the reduction of visibility. This analysis implies that the persistent low visibility is mainly resulted from small aerosol particles, including both scattering and absorbing particles. In order to improve the visibility in the Guangzhou region, the reduction of small particle emissions is urgently needed. This study suggests that there are two important steps to improve the visibility in Guangzhou. First, the aerosol concentration should be reduced to less than the threshold value (120μgm−3). Second, a further decrease in aerosols from its threshold value will lead to a significant improvement in visibility due to the non-linearity relationship between aerosol and visibility. [Copyright &y& Elsevier]

The formation of chemical oxidants, particularly ozone, in Mexico City were studied using a newly developed regional chemical/dynamical model (WRF-Chem). The magnitude and timing of simulated diurnal cycles of ozone (O3), carbon monoxide (CO) and nitrogen oxides (NO x ), and the maximum and minimum O3 concentrations are generally consistent with surface measurements. Our analysis shows that the strong diurnal cycle in O3 is mainly attributable to photochemical variations, while diurnal cycles of CO and NO x mainly result from variations of emissions and boundary layer height. In a sensitivity study, oxidation reactions of aromatic hydrocarbons (HCs) and alkenes yield highest peak O3 production rates (20 and 18ppbvh−1, respectively). Alkene oxidations, which are generally faster, dominate in early morning. By late morning, alkene concentrations drop, and oxidations of aromatics dominate, with lesser contributions from alkanes and CO. The sensitivity of O3 concentrations to NO x and HC emissions was assessed. Our results show that daytime O3 production is HC-limited in the Mexico City metropolitan area, so that increases in HC emissions increase O3 chemical production, while increases in NO x emissions decrease O3 concentrations. However, increases in both NO x and HC emissions yield even greater O3 increases than increases in HCs alone. Uncertainties in HC emissions estimates give large uncertainties in calculated daytime O3, while NO x emissions uncertainties are less influential. However, NO x emissions are important in controlling O3 at night. [Copyright &y& Elsevier]

Abstract: In this study, a regional dynamical model (WRF) is used to drive biogenic emission models to calculate high resolution (10×10 km) biogenic emissions of isoprene (C5H8), monoterpenes (C10H16), and nitric oxide (NO) in China. This high resolution biogenic inventory will be available for the community to study the effect of biogenic emissions on photochemical oxidants in China. The biogenic emissions are compared to anthropogenic emissions to gain insight on the potential impact of the biogenic emissions on tropospheric chemistry, especially ozone production in this region. The results show that the biogenic emissions in China exhibit strongly diurnal, seasonal, and spatial variations. The isoprenoid (including both isoprene and monoterpenes) emissions are closely correlated to tree density and strongly vary with season and local time. During winter (January), the biogenic isoprenoid emissions are the lowest, resulting from lower temperature and solar radiation, and highest in summer (July) due to higher temperature and solar radiation. The biogenic NO emissions are also higher during summer and lower during winter, but the magnitude of the seasonal variation is smaller than the emissions of isoprene and monoterpenes. The biogenic emissions of NO are widely spread out in the northern, eastern, and southern China regions, where high-density agricultural soil lands are located. Both biogenic NO and isoprenoid emissions are very small in western China. The calculated total biogenic emission budget is smaller than the total anthropogenic VOC emission budget in China. The biogenic isoprenoid and anthropogenic VOC emissions are 10.9 and 15.1 Tg year−1, respectively. The total biogenic and anthropogenic emissions of NO are 5.9 and 11.5 Tg(NO) year−1, respectively. The study shows that in central eastern China, the estimated biogenic emissions of isoprenoids are very small, and the anthropogenic emissions of VOCs are dominant in this region. However, in northeastern and southern China, there are relatively large biogenic emissions of isoprenoids, leading to an important impact on the ozone production in these regions. Furthermore, the emissions of isoprenoids are highest during summer and noontime, which correlates to the peak of ozone production period. For example, the ratio between summer and winter for the emissions of isoprenoids is about 15 in China. As a result, the biogenic emissions of isoprenoids are significantly larger than the anthropogenic emissions of VOCs in China during daytime in summer. Biogenic NO emissions are mostly produced by agricultural soils which co-exist with large populations and human activity. As a result, the biogenic emissions of NO are mostly overlapped with the anthropogenic emissions of NO, leading to the enhancement in NO concentrations in the high anthropogenic NO emission regions. Finally, the future emissions of isoprene and monoterpenes over China are estimated. The results show that the future biogenic emissions may increase significantly due to land cover changes in central eastern China, which could have a very important impact on ozone formation in this region. However, these estimates are highly uncertain and are presented as a potential scenario to show the importance of possible changes of biogenic emissions in China. [Copyright &y& Elsevier]

Abstract: Soluble aerosols are measured at Guangdong and Hainan Provinces of southern China. The measured chemical composition of aerosols includes F−, Cl−, , , Na+, , K+, Ca2+, and Mg2+. The locations of measurements include a mega city (Guangzhou), a medium city along the coastline (Haiko), a small city along the coastline (Shanya), and a remote island site in the South China Sea (Yongxing island). The results reveal that aerosols in this region are complex and heterogeneous. Sulfate aerosol () has the highest concentrations in Guangzhou (approximately 41% of total soluble aerosol mass), suggesting that anthropogenic activities (e.g., coal burning) play important roles in controlling aerosol concentrations in Guangzhou. By contrast, the concentrations of chlorine (Cl−) and sodium (Na+) are higher in Yongxing than in Guangzhou, indicating that the sea salt is the dominant aerosol in this marine environment site. In the medium (Haiko) and small (Shanya) city sites, the effects of anthropogenic and marine activities on aerosols fall in between the values in the mega city and the remote island site. The measured ratio of Cl−/Na+ shows that the ratio is less than 1.16 in all observation sites. The ratio in the Guangzhou city, the Haiko city, the Shanya city, and the Yongxing island is 0.52, 0.91, 0.24, and 0.53, respectively, indicating that significantly heterogeneous chemical reactions occur on sea salt particles. Unlike those in Europe and North America, there are high concentrations of calcium (Ca+) in all observation sites. The percentage of calcium mass to the measured total soluble aerosols mass is 21, 32, 34, and 30 at Guangzhou, Haiko, Sanya, and Yongxing, respectively. The calculations show that calcium plays an important role in neutralizing aerosols. The calculated “cation/anion” (∑[ion+]/∑[ion−]) ratio is 2.5, 2.5, 3.2, and 2.1, at Guangzhou, Haiko, Shanya, and Yongxing, respectively. The high “cation/anion” ratios suggest that , , and Cl− are neutralized, and the aerosols as a whole (internally mixed), appear to be in an alkaline mode in this region. However, without taking into account for calcium, the calculated “cation/anion” ratio reduces to 1.2, 0.98, 1.3, and 0.8 at Guangzhou, Haiko, Sanya, and Yongxing, respectively. The property of aerosols switches from an alkaline mode to an acidity mode at the Haiko and Yongxing sites. [Copyright &y& Elsevier]

Abstract: Satellite data (MODIS, GOME, and MOPITT) together with a chemical transport global model of the atmosphere (MOZART-2) are used to characterize air pollution in Eastern China and the Eastern US to assess the differences between the photochemical conditions in these two regions. Observations show that aerosol concentrations (both fine (radius<0.5μm) and coarse modes (radius>0.5μm)) are higher in Eastern China than in the Eastern US. The NO x concentrations in both regions are substantially higher than in remote regions such as over the oceans (150 compared to 5 (1014 #cm−2) over the Pacific Ocean). The CO concentrations are high in both urbanized areas (30 compared to 10 (1017 #cm−2) over the Pacific Ocean). However, the concentrations of non-methane hydrocarbons from both anthropogenic and biogenic sources are considerably lower in Eastern China than in the Eastern US. As a result, the rate of photochemical ozone production and ozone concentrations during summer is significantly lower in Eastern China (daily averaged concentrations of 40–50ppbv in summer) than in the Eastern US (daily averaged values of 60–70ppbv). The analysis also shows that in Eastern China, the O3 production is mainly due to the oxidation of carbon monoxide (54% of total O3 production), while, in the Eastern US, the O3 production is attributed primarily to the oxidation of reactive hydrocarbons (68% of total O3 production). The results also indicate that biogenic emissions of hydrocarbons contribute substantially to the production of O3 in the Eastern US. The O3 production due to the oxidation of biogenic hydrocarbons represents approximately one third of total O3 photochemical production in this region. Measurements of surface ozone in the Eastern US and Eastern China seem to support that the summer ozone production is lower in Eastern China than in the Eastern US. However, additional surface measurements, especially of reactive hydrocarbons and ozone are needed in Eastern China in order to improve the present analysis and to confirm our current conclusions. A sensitivity study shows that with increase in anthropogenic emissions of HCs, the surface ozone concentrations significantly increase in Eastern China, indicating that the increase in the emissions of HCs plays an important role for the enhancement in surface ozone in this region. [Copyright &y& Elsevier]

Abstract: Over the Guangzhou region, also called the Pearl River Delta (PRD) of Southern China, there are often high aerosol concentrations. The satellite (MODIS) data show that the aerosol optical depth is often higher than 0.6 in this area, which is known as Asian Brown Cloud region. In some extreme events, these high aerosol levels have caused very low visibilities. In this paper, we will show that on 2 November 2003, the daily average visibility is less than 2km (the instantaneous value is less than 200m), and the aerosol optical depth is greater than 1.2. We analyze the cause of this particular event. The analysis indicates that this event is related to the hurricane of “Melor 0319”. The hurricane is located at the northwest Philippines on 2 November 2003, and the Guangzhou region is outside the hurricane. The hurricane produces a strong descent motion in the lower troposphere, a weak surface wind speed, and a relatively low planetary boundary layer (PBL) in the Guangzhou region. As a result, the strong subsidence causes descending air motions to force the aerosol particles into a very shallow layer, and the weak horizontal wind acts to keep the aerosol particles inside the source region, producing very high aerosol concentrations and extremely low visibility in the Guangzhou region on 2 November 2003. This case analysis will be useful to better understand the causes of the poor air quality over Guangzhou, which is a first step for ultimately improving it in the future. For example, one can reduce emissions when synoptic conditions are expected to cause recurrences of the phenomenon discussed in the paper. [Copyright &y& Elsevier]

Abstract: In recent years, China and other emerging countries have been experiencing severe air pollution problems with high concentrations of atmospheric aerosol particles. Satellite measurements indicate that the aerosol loading of the atmosphere in highly populated regions of China is about 10 times higher than, for example, in Europe and in the Eastern United States. The exposure to extremely high aerosol concentrations might lead to important human health effects, including respiratory and cardiovascular diseases as well as lung cancers. Here, we analyze 52-year historical surface measurements of haze data in the Chinese city of Guangzhou, and show that the dramatic increase in the occurrence of air pollution events between 1954 and 2006 has been followed by a large enhancement in the incidence of lung cancer. [Copyright &y& Elsevier]

Urban dust pollution has been becoming an outstanding environmental problem due to rapid urbanization in China. However, it is very difficult to construct an urban dust inventory, owing to its small horizontal scale and strong temporal/spatial variability. With the analysis of visual interpretation, maximum likelihood classification, extrapolation and spatial overlaying, we quantified dust source distributions of urban constructions, barrens and croplands in the Guanzhong Basin using various satellite data, including VHR (0.5 m), Lansat-8 OLI (30 m) and MCD12Q1 (500 m). The croplands were the dominant dust sources, accounting for 40% (17,913 km 2 ) of the study area in summer and 36% (17,913 km 2 ) in winter, followed by barrens, accounting for 5% in summer and 10% in winter. Moreover, the total constructions were 126 km 2 , including 84% of active and 16% inactive. In addition, 59% of the constructions aggregated on the only megacity of the study area, Xi'an. With high accuracy exceeding 88%, the proposed satellite-data based method is feasible and valuable to quantify distributions of dust sources. This study provides a new perspective to evaluate regional urban dust, which is seldom quantified and reported. In a companied paper (Part-2 of the study), the detailed distribution of the urban dust sources is applied in a dynamical/aerosol model (WRF-Dust) to assess the effect of dust sources on aerosol pollution. [ABSTRACT FROM AUTHOR]

We developed a regional dust dynamical model (WRF-Dust) to simulate surface dust concentrations in the Guanzhong (GZ) basin of China during two typical dust cases (19th Aug. and 26th Nov., 2013), and compared model results with the surface measurements at 17 urban and rural sites. The important improvement of the model is to employ multiple high-resolution (0.5–500 m) remote sensing data to construct dust sources. The new data include the geographic information of constructions, croplands, and barrens over the GZ basin in summer and winter of 2013. For the first time, detailed construction dust emissions have been introduced in a regional dust model in large cities of China. Our results show that by including the detailed dust sources, model performance at simulating dust pollutions in the GZ basin is significantly improved. For example, the simulated dust concentration average for the 17 sites increases from 28 μg m − 3 to 59 μg m − 3 , closing to the measured concentration of 66 μg m − 3 . In addition, the correlation coefficient (r) between the calculated and measured dust concentrations is also improved from 0.17 to 0.57, suggesting that our model better presents the spatial variation. Further analysis shows that urban construction activities are the crucial source in controlling urban dust pollutions. It should be considered by policy makers for mitigating particulate air pollution in many Chinese cities. [ABSTRACT FROM AUTHOR]

The causes of haze formation in Beijing, China were analyzed based on a comprehensive measurement, including PBL (planetary boundary layer), aerosol composition and concentrations, and several important meteorological parameters such as visibility, RH (relative humidity), and wind speed/direction. The measurement was conducted in an urban location from Nov. 16, 2012 to Jan. 15, 2013. During the period, the visibility varied from > 20 km to less than a kilometer, with a minimum visibility of 667 m, causing 16 haze occurrences. During the haze occurrences, the wind speeds were less than 1 m/s, and the concentrations of PM 2.5 (particle matter with radius less than 2.5 μm) were often exceeded 200 μg/m 3 . The correlation between PM 2.5 concentration and visibility under different RH values shows that visibility was exponentially decreased with the increase of PM 2.5 concentrations when RH was less than 80%. However, when RH was higher than 80%, the relationship was no longer to follow the exponentially decreasing trend, and the visibility maintained in very low values, even with low PM 2.5 concentrations. Under this condition, the hygroscopic growth of particles played important roles, and a large amount of water vapor acted as particle matter (PM) for the reduction of visibility. The variations of meteorological parameters (RH, PBL heights, and WS (wind speed)), chemical species in gas-phase (CO, O 3 , SO 2 , and NOx), and gas-phase to particle-phase conversions under different visibility ranges were analyzed. The results show that from high visibility (> 20 km) to low visibility (< 2 km), the averaged PBL decreased from 1.24 km to 0.53 km; wind speeds reduced from 1 m/s to 0.5 m/s; and CO increased from 0.5 ppmv to 4.0 ppmv, suggesting that weaker transport/diffusion caused the haze occurrences. This study also found that the formation of SPM (secondary particle matter) was accelerated in the haze events. The conversions between SO 2 and SO 4 as well as NOx to NO 3 − increased, especially under high humidity conditions. When the averaged RH was 70%, the conversions between SO 2 and SO 4 accounted for about 20% concentration of PM 2.5 , indicating that formation of secondary particle matter had important contribution for the haze occurrences in Beijing. [ABSTRACT FROM AUTHOR]

Abstract: In-situ aircraft measurements of aerosols and clouds of 7 flights during the period from July to September of 2008 are analyzed in Beijing, China. The measured aerosol concentrations indicated that the Beijing region was highly polluted by aerosol particles. The impact of heavy aerosol particle loadings on cloud formation is studied. The microphysical characters of clouds (including number concentrations of cloud droplets (Nc), cloud droplet radius (Rc), liquid water content (LWC)), and number concentrations of aerosol particles (Na) were measured during the experiments. The aircraft measurements indicated that under high aerosol particle conditions, large number of cloud droplets was formed with small size of droplets. By contrast, under low aerosol particle conditions, the formation of cloud droplets was limited by the number of Na. In this case, small number of cloud droplets was formed with large size of droplets. The number concentrations of cloud droplets were sensitivity to LWC under high aerosol particle conditions. With low LWC value (<0.1gm−3), the Nc was slowly increased with the Na. For example, the cloud droplets were increased from 200 to 300cm−3, while aerosol particles were increased from 1000 to 6000cm−3, indicating that a large amount of aerosol particles were unchanged under low LWC condition. By contrast, with high LWC value (>0.5gm−3), the activation of aerosol particles to become cloud droplets was significantly enhanced. For example, the cloud droplets were increased from 700 to 1900cm−3, while aerosol particles were increased from 1000 to 6000cm−3, suggesting that a large amount of aerosol particles were converted to cloud droplets when there were enough LWC for supporting such conversions. This study also suggests that the Rc was also very sensitivity to the LWC values. The increase in the LWC values led to significant increase in the size of cloud droplets. [Copyright &y& Elsevier]

Abstract: Volatile organic compounds (VOCs) were measured from 2007 to 2010 at the center of Shanghai, China. Because VOCs are important precursors for ozone photochemical formation, detailed information of VOC sources needs to be investigated. The results show that the measured VOC concentrations in Shanghai are dominated by alkanes (43%) and aromatics (30%), following by halo-hydrocarbons (14%) and alkenes (6%). Based on the measured VOC concentrations, a receptor model (PMF; positive matrix factorization) coupled with the information related to VOC sources (the distribution of major industrial complex, meteorological conditions, etc.) is applied to identify the major VOC sources in Shanghai. The result shows that seven major VOC sources are identified by the PMF method, including (1) vehicle related source which contributes to 25% of the measured VOC concentrations, (2) solvent based industrial source to 17%, (3) fuel evaporation to 15%, (4) paint solvent usage to 15%, (5) steel related industrial production to 12%, (6) biomass/biofuel burning to 9%, and (7) coal burning to 7%. Furthermore, ozone formation potential related to VOC sources is calculated by the MIR (maximum incremental reactivity) technique. The most significant VOC source for ozone formation potential is solvent based industrial sources (27%), paint solvent usage (24%), vehicle related emissions (17%), steel related industrial productions (14%), fuel evaporations (9%), coal burning (6%), and biomass/biofuel burning (3%). The weekend effect on the VOC concentrations shows that VOC concentrations are generally higher in the weekdays than in the weekends at the sampling site, suggesting that traffic conditions and human activities have important impacts on the VOC emissions in Shanghai. [ABSTRACT FROM AUTHOR]

Abstract: In this study, aerosol vertical distributions of 17 in-situ aircraft measurements during 2005 and 2006 springs are analyzed. The 17 flights are carefully selected to exclude dust events, and the analyses are focused on the vertical distributions of aerosol particles associated with anthropogenic activities. The results show that the vertical distributions of aerosol particles are strongly affected by weather and meteorological conditions, and 3 different types of aerosol vertical distributions corresponding to different weather systems are defined in this study. The measurement with a flat vertical gradient and low surface aerosol concentrations is defined as type-1; a gradual decrease of aerosols with altitudes and modest surface aerosol concentrations is defined as type-2; a sharp vertical gradient (aerosols being strongly depressed in the PBL) with high surface aerosol concentrations is defined as type-3. The weather conditions corresponding to the 3 different aerosol types are high pressure, between two high pressures, and low pressure systems (frontal inversions), respectively. The vertical mixing and horizontal transport for the 3 different vertical distributions are analyzed. Under the type-1 condition, the vertical mixing and horizontal transport were rapid, leading to strong dilution of aerosols in both vertical and horizontal directions. As a result, the aerosol concentrations in PBL (planetary boundary layer) were very low, and the vertical distribution was flat. Under the type-2 condition, the vertical mixing was strong and there was no strong barrier at the PBL height. The horizontal transport (wind flux) was modest. As a result, the aerosol concentrations were gradually reduced with altitude, with modest surface aerosol concentrations. Under the type-3 condition, there was a cold front near the region. As a result, a frontal inversion associated with weak vertical mixing appeared at the top of the inversion layer, forming a very strong barrier to prevent aerosol particles being exchanged from the PBL height to the free troposphere. As a result, the aerosol particles were strongly depressed in the PBL height, producing high surface aerosol concentrations. The measured vertical aerosol distributions have important implications for studying the effects of aerosols on photochemistry. The J[O3] values are reduced by 11%, 48%, and 50%, under the type-1, type-2, and type-3 conditions, respectively. This result reveals that atmospheric oxidant capacity (OH concentrations) is modestly reduced under the type-1 condition, but is significantly reduced under the type-2 and type-3 conditions. This result also suggests that the effect of aerosol particles on surface solar flux is an integrated column effect, and detailed vertical distributions of aerosol particles are very important for assessing the impacts of aerosol on photochemistry. [Copyright &y& Elsevier]

Abstract: It is well known that nocturnal planetary boundary layer (NPBL) has important effects on urban air pollutants. However, the direct measurements of the interactions between the NPBL height and urban air pollutants are normally difficult, because such measurements require continuous vertical profiles of air pollutants and meteorological parameters. This paper provides an unique data, which temperature, NPBL, NO x and O3 concentrations are measured at a 250-m meteorological tower in the city of Tianjin, China (a much polluted city located in central-eastern China). The results are analyzed to study the trend of NPBL and the impacts of NPBL on air pollutants in the city. The results show that the measured NPBL height ranges from 100m to 150m. The measurement of 10-year trend of the NPBL height suggests that the averaged NPBL height increases by about 20% between 1995 and 2006. The results also show that the NPBL height has important effects on air pollutants. This study suggests that NO x and O3 concentrations are strongly anti-correlated inside of the NPBL height. During nighttime, NO x is directly emitted from the surface and is limited to inside of NPBL (40m), resulting in high NO x concentrations near the surface. The high NO x concentrations depress O3, producing low O3 concentrations near the surface. The measurements of vertical gradient of O3 show that about 30–50ppbv of O3 concentrations are chemically destroyed due to the surface emission of NO x during nighttime, suggesting that NPBL plays important roles in regulating the diurnal cycle of O3 at the surface. [Copyright &y& Elsevier]

In this study, air pollutants, including ozone (O3), nitrogen oxides (NO x =NO+NO2), carbon monoxides (CO), sulfur dioxide (SO2), and volatile organic compounds (VOCs) measured in the Yangtze River Delta (YRD) region during several air flights between September/30 and October/11 are analyzed. This measurement provides horizontal and vertical distributions of air pollutants in the YRD region. The analysis of the result shows that the measured O3 concentrations range from 20 to 60ppbv. These values are generally below the US national standard (84ppbv), suggesting that at the present, the O3 pollutions are modest in this region. The NO x concentrations have strong spatial and temporal variations, ranging from 3 to 40ppbv. The SO2 concentrations also have large spatial and temporal variations, ranging from 1 to 35ppbv. The high concentrations of CO are measured with small variations, ranging from 3 to 7ppmv. The concentrations of VOCs are relatively low, with the total VOC concentrations of less than 6ppbv. The relative small VOC concentrations and the relative large NO x concentrations suggest that the O3 chemical formation is under a strong VOC-limited regime in the YRD region. The measured O3 and NO x concentrations are strongly anti-correlated, indicating that enhancement in NO x concentrations leads to decrease in O3 concentrations. Moreover, the O3 concentrations are more sensitive to NO x concentrations in the rural region than in the city region. The ratios of Δ[O3]/Δ[NO x ] are −2.3 and −0.25 in the rural and in the city region, respectively. In addition, the measured NO x and SO2 concentrations are strongly correlated, highlighting that the NO x and SO2 are probably originated from same emission sources. Because SO2 emissions are significantly originated from coal burnings, the strong correlation between SO2 and NO x concentrations suggests that the NO x emission sources are mostly from coal burned sources. As a result, the future automobile increases could lead to rapid enhancements in O3 concentrations in the YRD region. [Copyright &y& Elsevier]

In this study, we will present evidence that aerosol particles have strong effects on the surface ozone concentration in a highly polluted city in China. The measured aerosol (PM10), UV flux, and O3 concentrations were analyzed from 1 November (1 Nov) to 7 November (7 Nov) 2005 in Tianjin, China. During this period, the aerosol concentration had a strong day-by-day variation, ranging from 0.2 to 0.6mgm−3. The ozone concentration also shows a strong variability in correlation with the aerosol concentration. During 1 Nov, 2 Nov, 6 Nov, and 7 Nov, the ozone concentration was relatively high (about 30–35ppbv; defined as a high-ozone period), and during 3 Nov to 5 Nov, the ozone concentration was relatively low (about 5–20ppbv; defined as a low-ozone period). The analysis of the measurement shows that the ozone concentration is strongly correlated to the measured UV flux. Because there were near cloud-free conditions between 1 Nov and 7 Nov, the variation of the UV flux mainly resulted from the variation of aerosol concentration. The result shows that higher aerosol concentrations produce a lower UV flux and lower ozone concentrations. By contrast, the lower aerosol concentration leads to a higher UV flux and higher ozone concentrations. A chemical mechanism model (NCAR MM) is applied to interpret the measurement. The model result shows that the extremely high aerosol concentration in this polluted city has a very strong impact on photochemical activities and ozone formation. The correlation between aerosol and ozone concentrations appears in a non-linear feature. The O3 concentration is very sensitive to aerosol loading when aerosol loading is high, and this sensitivity is reduced when aerosol loading is low. For example, the ratio of Δ[O3]/Δ[AOD] is about −16ppbvAOD−1 when AOD is less than 2, and is only −4ppbvAOD−1 when AOD is between 2 and 5. This result implies that a future decrease in aerosol loading could lead to a rapid increase in the O3 concentration in this region. [Copyright &y& Elsevier]

Abstract: Using optical spectrometer probes mounted on a light aircraft, fine-mode and coarse-mode aerosol size distributions were recorded within and above the planetary boundary layer in the vicinity of Beijing on 29 April 2005. A regional transport and dynamical model (Weather Research and Forecast coupled with a tracer transport model—WRF-Tracer) and satellite (moderate-resolution imaging spectroradiometer—MODIS) data were applied to analyze and interpret the aircraft measurements. The results show that the aerosol pollution in the Beijing region was very heavy on 29 April 2005. The satellite measured aerosol optical depth (AOD) over this region was exceeded to 2.0. The aerosol mass concentrations reached up to 160μgm−3 in some cases. The analysis suggests that three important source regions influenced this heavy aerosol pollution in the Beijing region, including: (1) the long-range transport from the Gobi Desert with diameters ranging from 0.5 to 4μm, (2) the transport from the south of Beijing area, and (3) the local emissions over Beijing. A strong vertical gradient of aerosol concentrations in Beijing at Shahe Airport was observed. The fine aerosol particles are dominated below the planetary boundary layer (PBL) with number concentrations of 5000cm−3, diameters of 0.3μm, and mass concentrations of 144μgcm−3. However, the coarse aerosol particles (dust) are dominated above the PBL with number concentrations of 2.5cm−3, diameters of 2.5μm, and mass concentrations of 120μgm−3. There is an inversion layer at the top of the PBL, and this inversion layer acts to suppress mixing between the PBL and overriding troposphere and stabilizes desert dust layer that is being transported overhead. This study demonstrates that the measurement from the aircraft together with the WRF-tracer and MODIS data provides good information to understand the origins and spatial distribution of aerosol particles in Beijing. Note that this analysis is based on the measurement on 29 April 2005. Thus it is considered as an example or a case study. [Copyright &y& Elsevier]

Ozone has become a major atmospheric pollutant in the North Central Plain (NCP) of China. Comprehensive measurements concerning the vertical profiles and photochemical formation mechanisms of typical O 3 pollution episode during August 8–13, 2018 were conducted in the NCP. A maximum hourly ozone concentration of 346 μg/m3 was observed on Aug 10, in which the surface O 3 photochemistry was under a strong VOC-limited regime, and the ratio of VOC to NO X ranged from 4:1 to 4:3, with ethylene, toluene, xylene, and propene providing large contributions to O 3 chemical production. The vertical measurements of O 3 , NO X , and the planetary boundary layer (PBL) height suggested that there were three different layers of photochemical O 3 production from the surface to 1.1 km. The first layer was from the surface to 200 m, with high NO concentrations leading to a strong conversion between O 3 and NO 2. The surface O 3 concentration was significantly lower than at 220 m during nighttime and early morning, with an average O 3 of approximately 60 μg/m3 and the maximum vertical gradient appearing in the early morning. Diurnal variations of NO 2 and N O 2 were significantly inversely correlated with O 3 and O 3. In the second vertical layer between 200 m and 1000 m the value of d[O 3 ]/dt ranged from 10 to 40 μg/m3/h, and the maximum chemical production of O 3 occurred at 300 m. The third layer was located outside the PBL height, where O 3 precursors with short chemical lifetimes rapidly decreased, producing weak chemical O 3 production. • A comprehensive measurement during high O3 period was conducted in NCP. • The O 3 pollutions were very high in NCP. • Surface O 3 photochemistry was under strong VOCs-limited regime. • 3 different layers existed for photochemical O 3 production in vertical directions. [ABSTRACT FROM AUTHOR]