Two Inversion Layers and Their Impacts on PM2.5 Concentration over the Yangtze River Delta, China

2019 ◽  
Vol 58 (11) ◽  
pp. 2349-2362 ◽  
Author(s):  
Yiwen Xu ◽  
Bin Zhu ◽  
Shuangshuang Shi ◽  
Yong Huang
Keyword(s):  
Boundary Layer ◽  
Vertical Distribution ◽  
Rural Area ◽  
Yangtze River ◽  
Layer Structure ◽  
Yangtze River Delta ◽  
Emission Sources ◽  
The Yangtze River ◽  
The Vertical Distribution ◽  
The Yangtze River Delta

AbstractAn integrated winter field campaign was conducted to investigate the atmospheric boundary layer structure and PM2.5 concentration at three sites over the Yangtze River delta (YRD) in China: Shouxian (a rural area), a site in a northern suburb of Nanjing, and Dongshan (a residential area). Two temperature inversion layers and air pollution events occurred simultaneously from 30 to 31 December 2016, local time, over the YRD. It was found that the two inversion layers were related to the presence of a high pressure system, resulting in divergence in the upper boundary layer and radiative cooling near the ground at night. Dominated by agricultural and residential biomass burning, the surface emission sources from the Shouxian rural area were moderately strong. After the formation of the two inversions, the vertical distribution of PM2.5 concentration below the upper inversion layer was uniform as a result of thorough boundary layer mixing in the earlier hours. During nighttime at the Nanjing site, air pollutant plumes from nearby elevated point sources could not easily diffuse downward/upward between the two inversion layers, which led to a distinct peak in the PM2.5 concentration. At the Dongshan site, the emission sources were weak and the nighttime PM2.5 concentration above 100 m was high. The surface PM2.5 concentration gradually increased from early morning to noon, which was attributed to emissions related to the local residents. The results indicated that the vertical distribution of pollutants was affected by a combination of local emissions, vertical boundary layer structure, and horizontal and vertical transports.

scholarly journals An important mechanism of regional O<sub>3</sub> transport for summer smog over the Yangtze River Delta in eastern China

2018 ◽  
Vol 18 (22) ◽  
pp. 16239-16251 ◽  
Author(s):  
Jun Hu ◽  
Yichen Li ◽  
Tianliang Zhao ◽  
Jane Liu ◽  
Xiao-Ming Hu ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Yangtze River ◽  
Eastern China ◽  
Yangtze River Delta ◽  
The Yangtze River ◽  
Convective Boundary ◽  
Summer Smog ◽  
The Yrd ◽  
Surface O3 ◽  
The Yangtze River Delta

Abstract. Severe ozone (O3) pollution episodes plague a few regions in eastern China at certain times of the year, e.g., the Yangtze River Delta (YRD). However, the formation mechanisms, including meteorological factors, contributing to these severe pollution events remain elusive. A severe summer smog stretched over the YRD region from 22 to 25 August 2016. This event displayed hourly surface O3 concentrations that exceeded 300 µg m−3 on 25 August in Nanjing, an urban area in the western YRD. The weather pattern during this period was characterized by near-surface prevailing easterly winds and continuous high air temperatures. The formation mechanism responsible for this O3 pollution episode over the YRD region, particularly the extreme values over the western YRD, was investigated using observation data and by running simulations with the Weather Research and Forecasting model with Chemistry (WRF-Chem). The results showed that the extremely high surface O3 concentration in the western YRD area on 25 August was largely due to regional O3 transport in the nocturnal residual layer (RL) and the diurnal change in the atmospheric boundary layer. On 24 August, high O3 levels, with peak values of 220 µg m−3, occurred in the daytime mixing layer over the eastern YRD region. During nighttime from 24 to 25 August, a shallow stable boundary layer formed near the surface which decoupled the RL above it from the surface. Ozone in the decoupled RL remained quite constant, which resulted in an O3-rich “reservoir” forming in this layer. This reservoir persisted due to the absence of O3 consumption from nitrogen oxide (NO) titration or dry deposition during nighttime. The prevailing easterly winds in the lower troposphere governed the regional transport of this O3-rich air mass in the nocturnal RL from the eastern to the western YRD. As the regional O3 transport reached the RL over the western YRD, O3 concentrations in the RL accumulated and rose to 200 µg m−3 over the western Nanjing site during the sunrise hours on 25 August. The development of the daytime convective boundary layer after sunrise resulted in the disappearance of the RL, as the vertical mixing in the convective boundary layer uniformly redistributed O3 from the upper levels via the entrainment of O3-rich RL air down to the O3-poor air at the ground. This net downward transport flux reached up to 35 µg m−3 h−1, and contributed a considerable surface O3 accumulation, resulting in severe daytime O3 pollution during the summer smog event on 25 August in the western YRD region. The mechanism of regional O3 transport through the nocturnal RL revealed in this study has great implications regarding understanding O3 pollution and air quality change.

scholarly journals An important mechanism of regional O<sub>3</sub> transport for summer smog over the Yangtze River Delta in East China

2018 ◽  
Author(s):  
Jun Hu ◽  
Yichen Li ◽  
Tianliang Zhao ◽  
Jane Liu ◽  
Xiao-Ming Hu ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Air Quality ◽  
Yangtze River ◽  
Yangtze River Delta ◽  
The Yangtze River ◽  
Easterly Wind ◽  
Summer Smog ◽  
The Yrd ◽  
Surface O3 ◽  
The Yangtze River Delta

Abstract. Severe ozone (O3) pollution episodes plague a few regions in Eastern China at times, e.g., the Yangtze River Delta (YRD). The formation mechanisms including contributing meteorological factors of these severe pollution events remain elusive. A severe summer smog stretched over the YRD region from August 22 to 25, 2016 with hourly surface O3 concentrations exceeding 300 µg m−3 on August 25 in Nanjing, located in the western YRD. The weather pattern of this episode was characterized by near-surface prevailing easterly wind and continuous high air temperature. The formation mechanism of this O3 episode over the YRD area, particularly the extreme values over western YRD, was investigated using observation data and simulation with the Weather Research and Forecasting model with Chemistry (WRF-Chem). The O3 pollution episode was generally well simulated by the WRF-Chem air quality model. On August 24, the high O3 levels with the peak values of 250 µg m−3 occurred in the daytime mixing layer over the eastern YRD area. During nighttime, a shallow stable boundary layer formed near the surface, which decoupled the residual layer (RL) above it from the surface. O3 in the decoupled RL remained nearly constant, resulting an O3-rich reservoir, due to lack of NO titration and absence of dry deposition. The prevailing easterly wind in the lower troposphere transported the O3-rich air mass in the nocturnal RL from the eastern to western YRD. Consequently, the O3 concentrations in the RL over the western YRD area increased to 170 µg m−3 in the wee hours of August 25, 2016. Due to the growth of the convective boundary layer after the sunrise, entrainment of O3-rich RL air and boundary layer mixing contributed considerably to the rapid increase of surface O3. Process analysis indicated vertical mixing contributed ~ 40 µg m−3 h−1 of O3 accumulation over Nanjing in the morning of August 25, 2016, which played an important role in contributing to the severe daytime O3 pollution in the western YRD area. The mechanism of regional O3 transport through the nocturnal RL has a great implication for understanding O3 pollution in air quality change.

Assessment of short-term PM2.5-related mortality due to different emission sources in the Yangtze River Delta, China

2015 ◽  
Vol 123 ◽  
pp. 440-448 ◽  
Author(s):  
Jiandong Wang ◽  
Shuxiao Wang ◽  
A. Scott Voorhees ◽  
Bin Zhao ◽  
Carey Jang ◽  
...  
Keyword(s):  
Yangtze River ◽  
Yangtze River Delta ◽  
River Delta ◽  
Emission Sources ◽  
The Yangtze River ◽  
Short Term ◽  
The Yangtze River Delta ◽  
Related Mortality

scholarly journals Examining the major contributors of ozone pollution in a rural area of the Yangtze River Delta region during harvest season

2015 ◽  
Vol 15 (11) ◽  
pp. 6101-6111 ◽  
Author(s):  
X. Pan ◽  
Y. Kanaya ◽  
H. Tanimoto ◽  
S. Inomata ◽  
Z. Wang ◽  
...  
Keyword(s):  
Production Rate ◽  
Rural Area ◽  
Yangtze River ◽  
Yangtze River Delta ◽  
The Yangtze River ◽  
Delta Region ◽  
Photochemical Production ◽  
Yangtze River Delta Region ◽  
The Yangtze River Delta

Abstract. Open biomass burning (OBB) emits significant amounts of non-methane hydrocarbons (NMHCs), and the mixing of OBB with urban plumes could exacerbate regional ozone (O3) pollution. In the present study, an observational field campaign was performed in a rural area at the northern edge of the Yangtze River Delta region (YRDR) from 15 May to 24 June 2010, during intensive open burning of wheat residues. The net photochemical production rate of oxidant (Ox = O3 + NO2) at the site was evaluated based on a box model (Regional Atmospheric Chemical Mechanism, Version 2) constrained by real-time ambient measurements (e.g., O3, volatile organic compounds (VOCs), NOx (NO2 + NO), J values). Our results showed that both in situ photochemistry and direct transport from urban areas in the YRDR were responsible for the high Ox concentration at the site. During an OBB-impact case, net photochemical production of Ox in the daytime was pronounced, with a 6 h averaged Ox production rate of 13 ± 4 ppbv h−1 (maximum value of 21 ppbv h−1 at 12:00 CST). Photochemical Oxproduction changed from VOC-limited in the morning to NOx-limited in the afternoon due to the rapid photochemical consumption of NOx during the day. A combined analysis with positive matrix factorization demonstrated that O3 pollution in the rural area of the YRDR was largely affected by urban emission, and OBB-related emissions also contributed to in situ photochemical production, particularly in the afternoon. Our study suggested that a joint effort in reducing both NMHCs (e.g., aromatics) and NOx emissions in the urban area, as well as local OBB activities, may be effective in eliminating high-O3 pollution risk in the rural areas of the YRDR.

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