Numerical Air Quality Forecast over Eastern China: Development, Uncertainty and Future

Air pollution is severely focused due to its distinct effect on climate change and adverse effect on human health, ecological system, etc. Eastern China is one of the most polluted areas in the world and many actions were taken to reduce air pollution. Numerical forecast of air quality was proved to be one of the effective ways to help to deal with air pollution. This chapter will present the development, uncertainty and thinking about the future of the numerical air quality forecast emphasized in eastern China region. Brief history of numerical air quality modeling including that of Shanghai Meteorological Service (SMS) was reviewed. The operational regional atmospheric environmental modeling system for eastern China (RAEMS) and its performance on forecasting the major air pollutants over eastern China region was introduced. Uncertainty was analyzed meanwhile challenges and actions to be done in the future were suggested to provide better service of numerical air quality forecast

Air quality services on climate time-scales for decision making: An empirical study of China

The provision of climate services for assessing and governing environmental problems such as poor air quality requires interactions between scientists and decision-makers. Air quality information services in China mainly focus on the coming days to weeks. However, users may benefit from air quality information on climate time-scales—from months to decades; hereafter air quality climate services. We focused on key decision-makers and stakeholders that are users of air quality climate services and conducted five workshops with these identified users to ascertain their priorities for air quality climate services, and the reasoning behind these priorities. We also conducted a choice-based conjoint experiment via an online survey distributed amongst regional and local Climate Centres and Environmental Monitoring Centres to assess quantitatively the decision-makers’ needs. The results from the workshops and the survey showed that the needs for air quality climate services by users in China mainly relate to seasonal forecasting of winter haze events (PM2.5 levels and/or the meteorological conditions conducive to the dispersion of the air pollution); there is also some interest in long-term projections of haze under climate change and a growing interest in ozone pollution in summer. Spatial relevance is perceived to be important to regional and city-level stakeholders who prefer information on the city-level, whilst national-wide information is important for national government agencies. A high level of reliability of forecasts was needed for uptake. The findings on the needs for air quality climate services by potential users can support researchers and policy-makers in developing the scientific capacity and providing tailored and effective air quality climate services in China

The impact of Climate Change on the Western Pacific Subtropical High and the related ozone pollution in Shanghai, China

Severe ozone (O-3) episodes occur frequently in Shanghai during late-summers. We define geopotential height averaged over the key area region (122.5 degrees E-135 degrees E, 27.5 degrees N -35 degrees N) at 500 hPa as a WPSH_SHO3 index which has high positive correlation with surface O-3 concentration in Shanghai. In addition, the index has a significant long-term increasing trend during the recent 60 years. Analysis shows the meteorological conditions under the strong WPSH_SHO3 climate background (compared to the weak background) have several important anomalies: (1) A strong WPSH center occurs over the key area region. (2)The cloud cover is less, resulting in high solar radiation and low humidity, enhancing the photochemical reactions of O-3. (3) The near-surface southwesterly winds are more frequent, enhancing the transport of upwind pollutants and O-3 precursors from polluted regions to Shanghai and producing higher O-3 chemical productions. This study suggests that the global climate change could lead to a stronger WPSH in the key region, enhancing ozone pollution in Shanghai. A global chemical/transport model (MOZART-4) is applied to show that the O-3 concentrations can be 30 ppbv higher under a strong WPSH_SHO3 condition than a weak condition, indicating the important effect of the global climate change on local air pollution in Shanghai

Impact of the 2015 El Nino event on winter air quality in China

During the winter of 2015, there was a strong El Nino (ENSO) event, resulting in significant anomalies for meteorological conditions in China. Analysis shows that the meteorological conditions in December 2015 (compared to December 2014) had several important anomalies, including the following: (1) the surface southeasterly winds were significantly enhanced in the North China Plain (NCP); (2) the precipitation was increased in the south of eastern China; and (3) the wind speeds were decreased in the middle-north of eastern China, while slightly increased in the south of eastern China. These meteorological anomalies produced important impacts on the aerosol pollution in eastern China. In the NCP region, the PM2.5 concentrations were significantly increased, with a maximum increase of 80-100 mu g m(-3). A global chemical/transport model (MOZART-4) was applied to study the individual contribution of the changes in winds and precipitation to PM2.5 concentrations. This study suggests that the 2015El Nino event had significant effects on air pollution in eastern China, especially in the NCP region, including the capital city of Beijing, in which aerosol pollution was significantly enhanced in the already heavily polluted capital city of China

Meteorology driving the highest ozone level occurred during mid-spring to early summer in Shanghai, China

More recent studies highlighted the aggravated surface ozone (O-3) pollutions occurred in Spring and Autumn in China, but presenting clear distinctions for different cities. In this study, we observed the most elevated mean daily and maximum daily 8-h (MDA8) O-3 concentrations occurred from mid-Spring to early Summer (April, May and June, AMJ) at both urban and remote sites in Shanghai compared to other warm months (March, July, August, September, October), based on the long-term measurements from 2010 to 2019. The typical weather pattern of G-SW (High pressure with predominant winds of southwesterly) recognized by T-mode principal component approach (T-PCA), exhibits the strongest solar radiation and highest daily maximum temperature relative to other weathers in AMJ, leading to not only the most elevated O-3 concentration, but also the largest O-3 increasing variability in daytime. More importantly, under the G-SW weather condition, the MDA8 O-3 concentration presents the greatest increasing rate at 3.95 ppbv/yr from 2010 to 2019 in Shanghai downtown compared to other weather patterns, suggesting that more occurrence and faster exacerbation of O-3 pollutions could be expected under the G-SW weather condition in the future. To understand and mitigate high O-3 occurrences under the weather pattern of G-SW during AMJ, process analysis by a chemical/dynamical model (WRF-Chem, Weather Research and Forecasting (WRF) model coupled with Chemistry) is conducted to elucidate the strong O-3 productivity (19 ppbv/h in daytime), that dominates the high O-3 occurrence under the G-SW weather condition. Sensitive studies suggest that under the G-SW weather condition, reduction of VOCs emissions is very effective to prevent the high O-3 pollution in Shanghai. The model results show that photochemical productivity decreases by 35% in daytime response to 30% reduction of VOCs emissions, leading to 17.6% mitigation of peak O-3 concentration in Shanghai downtown. This result provides valuable information for the development of emission control strategy in Shanghai under different weather conditions. (C) 2021 Published by Elsevier B.V

Long-term measurements of planetary boundary layer height and interactions with PM2.5 in Shanghai, China

The planetary boundary layer (PBL) height plays important roles in modulating the local air pollution near surface, such as PM2.5 (particles with diameter <= 2.5 mu m) concentrations. However, it is very difficult to continuously measure a long-term PBL height. This study is the first time to analyze the long-term variability of PBL height (from 2010 to 2015) by using the continuous measurements from a micro-pulse Lidar (MPL) in Shanghai, China. The aim of this paper is to investigate the long-term variation of PBL height and its relationship with meteorological factors and PM2.5 concentration in the mega city of Shanghai, China. The results showed that there was no significant long-term trend of PBL height in Shanghai during the 6-year period with a mean value of 400 m, indicating the changes of air pollution during the same period were likely driven by other factors, e.g. wind speed or emissions. The PBL height was positively correlated with solar radiation and wind speed, while negatively correlated with vertical temperature gradient and PM(2.)(5 )concentration. By comparison, the PBL height was more sensitive to solar radiation and vertical temperature gradient, indicating that the variation of PBL height was mostly driving by thermal effect. The diurnal variation of PBL height had strong impact on the diurnal cycle of PM2.5 concentration. For example, the PM2.5 diurnal variation presented different patterns between summer and winter. In winter the PM2.5 diurnal cycle exhibited two-peaks pattern, appeared in the morning at 8:00 BJT and at night around 20:00 BJT respectively. Both peaks were well corresponding to the low PBL conditions (200-300 m). While in summer, the PM2.5 peaked at noon under high PBL condition (1000 m). This noon peak was likely due to the elevation of secondary aerosol formation, which offsets the diffusion effect on PM2.5 resulted from PBL developments. There was a strong interaction among the solar radiation, PBL, and PM2.5 concentration. The higher PM2.5 caused the reduction of solar radiation to inhibit PBL, further depressed the aerosols in a shallow layer to yield higher PM2.5 concentration. As a result, PBL and PM2.5 concentrations presented non-linearly anti-correlations. During the lower range of PBL (less than 400 m), the PM2.5 variability was very sensitive to the changes in the PBL. On the other hand PM 25 presented substantial effects on PBL evolutions. The daytime PBL developed more fully under low PM2.5 conditions compared with that under high PM2.5 levels. The PBL height decreased about 100 m when PM2.5 concentration increased about 30-50 mu g/m(3) under the condition that daily PM 2 . 5 concentration was greater than 70 mu g/m 3 . The statistical analysis showed that the mean ratios of PM2.5/PBL during 6-year period were 0.37, 0.11, 0.30, and 0.37 (mu g/m(4)) in spring, summer, autumn, and winter respectively, suggesting that the PM2.5 levels were more sensitive to PBL in spring and winter

Long-term trend of O-3 in a mega City (Shanghai), China: Characteristics, causes, and interactions with precursors

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 (NOx 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 NOx), 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 NOx concentrations at the urban site (XJH) from 2006 to 2015 (O-3 increasing 67% and NOx decreasing 38%), while there were very small trends of O-3 and NOx 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 NOx 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 NOx concentrations from 2006 to 2015 at the urban area of Shanghai were strongly anti-correlated, suggesting that the extremely high NOx concentration in the urban area depressed the O-3 concentrations. It is interesting to note that the anti-correlation between O-3 and NOx was in an un-linearly relationship. Under high O-3 concentration condition, the ratio of Delta[O-3]/Delta[NOx] was as large as - 1.5. In contrast, under low O-3 concentrations, the ratio of Delta[O-3]/Delta[NOx] was only - 0.2. This result suggested that when O-3 concentration was high, it was more sensitive to NOx concentration, while when O-3 concentration was low, it was less sensitive to NOx 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 NOx and VOCs are not only precursors for O-3, but also are important precursors for particular matter (PM). If reduction of NOx leads to decrease in PM, but increase in O-3, the NOx emission control become a very complicated issue and need to carefully design a comprehensive control method. (C) 2017 Elsevier B.V. All rights reserved

Black carbon (BC) in a northern Tibetan mountain: effect of Kuwait fires on glaciers

The black carbon (BC) deposition on the ice core at Muztagh Ata Mountain, northern Tibetan Plateau, was analyzed. Two sets of measurements were used in this study, which included the air samplings of BC particles during 2004-2006 and the ice core drillings of BC deposition during 1986-1994. Two numerical models were used to analyze the measured data. A global chemical transportation model (MOZART-4) was used to analyze the BC transport from the source regions, and a radiative transfer model (SNICAR) was used to study the effect of BC on snow albedo. The results show that during 1991-1992, there was a strong spike in the BC deposition at Muztagh Ata, suggesting that there was an unusual emission in the upward region during this period. This high peak of BC deposition was investigated by using the global chemical transportation model (MOZART-4). The analysis indicated that the emissions from large Kuwait fires at the end of the first Gulf War in 1991 caused this high peak of the BC concentrations and deposition (about 3-4 times higher than other years) at Muztagh Ata Mountain, suggesting that the upward BC emissions had important impacts on this remote site located on the northern Tibetan Plateau. Thus, there is a need to quantitatively estimate the effect of surrounding emissions on the BC concentrations on the northern Tibetan Plateau. In this study, a sensitivity study with four individual BC emission regions (Central Asia, Europe, the Persian Gulf, and South Asia) was conducted by using the MOZART-4 model. The result suggests that during the "normal period" (non-Kuwait fires), the largest effect was due to the Central Asia source (44 %) during the Indian monsoon period, while during the non-monsoon period, the largest effect was due to the South Asia source (34 %). The increase in radiative forcing increase (RFI) due to the deposition of BC on snow was estimated by using the radiative transfer model (SNICAR). The results show that under the fresh snow assumption, the estimated increase in RFI ranged from 0.2 to 2.5 W m(-2), while under the aged snow assumption, the estimated increase in RFI ranged from 0.9 to 5.7 W m(-2). During the Kuwait fires period, the RFI values increased about 2-5 times higher than in the "normal period", suggesting a significant increase for the snow melting on the northern Tibetan Plateau due to this fire event. This result suggests that the variability of BC deposition at Muztagh Ata Mountain provides useful information to study the effect of the upward BC emissions on environmental and climate issues in the northern Tibetan Plateau. The radiative effect of BC deposition on the snow melting provides important information regarding the water resources in the region

Air quality services on climate time-scales for decision making: An empirical study of China

The provision of climate services for assessing and governing environmental problems such as poor air quality requires interactions between scientists and decision-makers. Air quality information services in China mainly focus on the coming days to weeks. However, users may benefit from air quality information on climate time-scales—from months to decades; hereafter air quality climate services. We focused on key decision-makers and stakeholders that are users of air quality climate services and conducted five workshops with these identified users to ascertain their priorities for air quality climate services, and the reasoning behind these priorities. We also conducted a choice-based conjoint experiment via an online survey distributed amongst regional and local Climate Centres and Environmental Monitoring Centres to assess quantitatively the decision-makers’ needs. The results from the workshops and the survey showed that the needs for air quality climate services by users in China mainly relate to seasonal forecasting of winter haze events (PM2.5 levels and/or the meteorological conditions conducive to the dispersion of the air pollution); there is also some interest in long-term projections of haze under climate change and a growing interest in ozone pollution in summer. Spatial relevance is perceived to be important to regional and city-level stakeholders who prefer information on the city-level, whilst national-wide information is important for national government agencies. A high level of reliability of forecasts was needed for uptake. The findings on the needs for air quality climate services by potential users can support researchers and policy-makers in developing the scientific capacity and providing tailored and effective air quality climate services in China