scholarly journals The haze pollution under strong atmospheric oxidization capacity in summer in Beijing: Insights into the formation mechanism of atmospheric physicochemical process

2020 ◽  
Author(s):  
Dandan Zhao ◽  
Guangjing Liu ◽  
Jinyuan Xin ◽  
Jiannong Quan ◽  
Yuesi Wang ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Air Pollution ◽  
Potential Temperature ◽  
Particle Surface ◽  
Physicochemical Process ◽  
Joint Control ◽  
Pollution Transport ◽  
The South ◽  
Haze Pollution ◽  
Oxidation Ratio

Abstract. Under strong atmospheric oxidization capacity, haze pollution in the summer of Beijing was the result of the synergistic effect of physicochemical process in the atmospheric boundary layer (ABL). The south/southwest areas generally ~ 60–300 km far away from Beijing were seriously polluted, in contrast to a clean situation in Beijing. The southerly winds moving more than ~ 20–30 km h−1 since early morning primarily caused the initiation of haze pollution. The PM2.5 level increased to 75 μg m−3 in several hours at daytime, which was simultaneously affected by the ABL structure. Additionally, the O3 concentration was quite high at daytime (250 μg m−3), corresponding to a strong atmospheric oxidation capacity. Numerous sulfate and nitrate were formed through active atmospheric chemical processes, with sulfur oxidation ratio (SOR) up to ~ 0.76 and nitrogen oxidation ratio (NOR) increasing from 0.09 to 0.26, which further facilitated the particulate matter (PM) level rising. Even so, the increase in sulfate was mainly linked by southerly transport. At midnight, the PM2.5 concentration sharply increased from 75 μg m−3 to 150 μg m−3 in 4 hours and stayed the highest level till the next morning. With the premise of an extremely stable ABL structure, the formation of secondary aerosols dominated by nitrate was quite intense, driving the outbreak of haze pollution. PM levels in the south/southeast of Beijing were significantly lower than that in Beijing over this time, even below air quality standards, thus, the contribution of pollution transport was almost gone. With the formation of nocturnal stable boundary layer of 0–0.3 km altitude, the extremely low turbulence kinetic energy (TKE) of 0–0.05 m2 s−2 inhibited the spread of particles and moisture, ending up with elevated levels of PM2.5 and relative humidity (~ 90 %) near the surface. Under quite high humidity and strong ambient oxidization capacity, the NOR rapidly increased from 0.26 to 0.60 and heterogeneous hydrolysis reactions at the moist particle surface were very significant. The nitrate concentration explosively increased from 11.6 μg m−3 to 57.8 μg m−3, while the concentrations of sulfate and organics slightly increased by 6.1 μg m−3 and 3.1 μg m−3, respectively. With clean & strong winds passing through Beijing, the stable ABL was broken with potential temperature gradient turning to negative and ABL heights increasing to ~ 2.5 km. The strong turbulence activity with TKE of ~ 3–5 m2 s−2 notably promoted the pollution diffusion. The self-cleaning capacity of the atmosphere is always responsible for the dispersion of air pollution. Even so, reducing atmospheric oxidization capacity such as strengthening the collaborative control of nitrogen oxide (NOx) and volatile organic compounds (VOCs) was urgent, as well as continuously deepening regional joint control of air pollution.

scholarly journals Haze pollution under a high atmospheric oxidization capacity in summer in Beijing: insights into formation mechanism of atmospheric physicochemical processes

2020 ◽  
Vol 20 (8) ◽  
pp. 4575-4592 ◽  
Author(s):  
Dandan Zhao ◽  
Guangjing Liu ◽  
Jinyuan Xin ◽  
Jiannong Quan ◽  
Yuesi Wang ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Air Pollution ◽  
Particulate Matter ◽  
Potential Temperature ◽  
Equivalent Diameter ◽  
Pollution Transport ◽  
Aerosol Formation ◽  
Near Surface ◽  
Physicochemical Processes ◽  
Haze Pollution

Abstract. Under a high atmospheric oxidization capacity, the synergistic effect of the physicochemical processes in the atmospheric boundary layer (ABL) caused summer haze pollution in Beijing. The southern and southwestern areas, generally 60–300 km away from Beijing, were seriously polluted in contrast to Beijing, which remained clean. Southerly winds moving faster than 20–30 km h−1 since the early morning primarily caused haze pollution initiation. The PM2.5 (particulate matter with a dynamic equivalent diameter smaller than 2.5 µm) level increased to 75 µg m−3 over several hours during the daytime, which was simultaneously affected by the ABL structure. Additionally, the O3 concentration was quite high during the daytime (250 µg m−3), corresponding to a high atmospheric oxidation capacity. Much sulfate and nitrate were produced through active atmospheric chemical processes, with sulfur oxidation ratios (SORs) up to ∼0.76 and nitrogen oxidation ratios (NORs) increasing from 0.09 to 0.26, which further facilitated particulate matter (PM) level enhancement. However, the increase in sulfate was mainly linked to southerly transport. At midnight, the PM2.5 concentration sharply increased from 75 to 150 µg m−3 over 4 h and remained at its highest level until the next morning. Under an extremely stable ABL structure, secondary aerosol formation dominated by nitrate was quite intense, driving the haze pollution outbreak. The PM levels in the southern and southeastern areas of Beijing were significantly lower than those in Beijing at this time, even below air quality standards; thus, the contribution of pollution transport had almost disappeared. With the formation of a nocturnal stable boundary layer (NSBL) at an altitude ranging from 0–0.3 km, the extremely low turbulence kinetic energy (TKE) ranging from 0 to 0.05 m2 s−2 inhibited the spread of particles and moisture, ultimately resulting in elevated near-surface PM2.5 and relative humidity (∼90 %) levels. Due to the very high humidity and ambient oxidization capacity, NOR rapidly increased from 0.26 to 0.60, and heterogeneous hydrolysis reactions at the moist particle surface were very notable. The nitrate concentration steeply increased from 11.6 to 57.8 µg m−3, while the sulfate and organics concentrations slightly increased by 6.1 and 3.1 µg m−3, respectively. With clean and strong winds passing through Beijing, the stable ABL dissipated with the potential temperature gradient becoming negative and the ABL height (ABLH) increasing to ∼2.5 km. The high turbulence activity with a TKE ranging from 3 to 5 m2 s−2 notably promoted pollution diffusion. The self-cleaning capacity of the atmosphere is commonly responsible for air pollution dispersion. However, reducing the atmospheric oxidization capacity, through strengthening collaborative control of nitrogen oxide (NOx) and volatile organic compounds (VOCs), as well as continuously deepening regional joint air pollution control, is urgent.

scholarly journals Dome effect of black carbon and its key influencing factors: A one-dimensional modelling study

2017 ◽  
Author(s):  
Zilin Wang ◽  
Xin Huang ◽  
Aijun Ding
Keyword(s):  
Boundary Layer ◽  
Air Pollution ◽  
Black Carbon ◽  
Rural Areas ◽  
Land Surface ◽  
Critical Role ◽  
Aerosol Layer ◽  
Near Surface ◽  
Haze Pollution ◽  
The Impact

Abstract. Black carbon (BC) has been identified to play a critical role in aerosol-planet boundary layer (PBL) interaction and further deterioration of near-surface air pollution in megacities, which has been named as its dome effect. However, the impacts of key factors that influence this effect, such as the vertical distribution and aging processes of BC, and also the underlying land surface, have not been quantitatively explored yet. Here, based on available in-situ measurements of meteorology and atmospheric aerosols together with the meteorology-chemistry online coupled model, WRF-Chem, we conduct a set of parallel simulations to quantify the roles of these factors in influencing the BC's dome effect and surface haze pollution, and discuss the main implications of the results to air pollution mitigation in China. We found that the impact of BC on PBL is very sensitive to the altitude of aerosol layer. The upper level BC, especially those near the capping inversion, is more essential in suppressing the PBL height and weakening the turbulence mixing. The dome effect of BC tends to be significantly intensified as BC aerosol mixed with scattering aerosols during winter haze events, resulting in a decrease of PBL height by more than 25 %. In addition, the dome effect is more substantial (up to 15 %) in rural areas than that in the urban areas with the same BC loading, indicating an unexpected regional impact of such kind of effect to air quality in countryside. This study suggests that China's regional air pollution would greatly benefit from BC emission reductions, especially those from the elevated sources from the chimneys and also the domestic combustions in rural areas, through weakening the aerosol-boundary layer interactions that triggered by BC.

Observational Evaluation of a Convective Quasi-Equilibrium View of Monsoons

2010 ◽  
Vol 23 (16) ◽  
pp. 4416-4428 ◽  
Author(s):  
Ji Nie ◽  
William R. Boos ◽  
Zhiming Kuang
Keyword(s):  
Boundary Layer ◽  
South Asian ◽  
Asian Monsoon ◽  
Potential Temperature ◽  
South Asian Monsoon ◽  
Quasi Equilibrium ◽  
Tropospheric Temperature ◽  
The South ◽  
Layer Potential ◽  
The North

Abstract Idealized dynamical theories that employ a convective quasi-equilibrium (QE) treatment for the diabatic effects of moist convection have been used to explain the location, intensity, and intraseasonal evolution of monsoons. This paper examines whether observations of the earth’s regional monsoons are consistent with the assumption of QE. It is shown here that in local summer climatologies based on reanalysis data, maxima of free-tropospheric temperature are, indeed, nearly collocated with maxima of subcloud equivalent potential temperature, θeb, in all monsoon regions except the North and South American monsoons. Free-tropospheric temperatures over North Africa also exhibit a strong remote influence from the South Asian monsoon. Consistent with idealized dynamical theories, peak precipitation falls slightly equatorward of the maxima in θeb and free-tropospheric temperature in regions where QE seems to hold. Vertical structures of temperature and wind reveal two types of monsoon circulations. One is the deep, moist baroclinic circulation clearly seen in the South Asian monsoon. The other is of mixed type, with the deep moist circulation superimposed on a shallow dry circulation closely associated with boundary layer temperature gradients. While the existence of a shallow dry circulation has been documented extensively in the North African monsoon, here it is shown to also exist in Australia and southern Africa during the local summer. Analogous to moist QE theories for the deep circulation, the shallow circulation can be viewed in a dry QE framework in which shallow ascent occurs just equatorward of the peak boundary layer potential temperature, θb, providing a unified system where the poleward extents of deep and shallow circulations are bounded by maxima in θeb and θb, respectively.

scholarly journals Multiple technical observations of the atmospheric boundary layer structure of a red warning haze episode in Beijing

2019 ◽  
Author(s):  
Yu Shi ◽  
Fei Hu ◽  
Guangqiang Fan ◽  
Zhe Zhang
Keyword(s):  
Boundary Layer ◽  
Air Pollution ◽  
Atmospheric Boundary Layer ◽  
Extinction Coefficient ◽  
Layer Structure ◽  
Low Frequency ◽  
Inverse Correlation ◽  
Hygroscopic Growth ◽  
Boundary Layer Structure ◽  
Haze Pollution

Abstract. The study and control of air pollution need to detect the structure of atmospheric boundary layer (ABL) in order to understand the mechanism of interaction between atmospheric boundary layer and air pollution. However, when extreme pollution occurs, the detection of atmospheric boundary layer structure is very scarce. Beijing, the capital of China, has experienced a severe haze pollution in December 2016. The city issued its first red air pollution warning of this year (the highest PM2.5 concentration was later monitored to exceed 450 μg m−3). In this paper, the vertical profiles of wind, temperature, humidity and extinction coefficient (reflecting aerosol concentration), as well as ABL heights and turbulence quantities under heavy haze pollution are analyzed, with collected data from Lidar, wind profile radar (WPR), radiosonde, 325-meter meteorological tower (equipped with 7-layer supersonic anemometer and 15-layer low frequency wind, temperature and humidity sensors) and some other ground observations. ABL heights obtained by three different methods based on Lidar extinction coefficient data (Hc) are compared with the heights calculated from radiosonde temperature data (Hθ) and from WPR wind speed data (Hu). The results show that increase of water vapor has greatly promoted the hygroscopic growth of aerosols, the corresponding extinction coefficients also increased significantly. The PBL heights Hθ and Hu of heavy haze pollution day were generally lower than those of clean day, but Hc increased. Turbulent activities were great inhibited during haze pollution, time changes of both friction velocity (u*) and turbulent kinetic energy (TKE) have obvious inverse correlation with that of PM2.5. The results of this paper could provide some reference for the parameterization of the boundary layer height and turbulent diffusion process in the numerical model of severe air pollution.

scholarly journals Multiple technical observations of the atmospheric boundary layer structure of a red-alert haze episode in Beijing

2019 ◽  
Vol 12 (9) ◽  
pp. 4887-4901 ◽  
Author(s):  
Yu Shi ◽  
Fei Hu ◽  
Guangqiang Fan ◽  
Zhe Zhang
Keyword(s):  
Boundary Layer ◽  
Air Pollution ◽  
Atmospheric Boundary Layer ◽  
Extinction Coefficient ◽  
Layer Structure ◽  
Heat Fluxes ◽  
Sensible Heat ◽  
Boundary Layer Structure ◽  
Haze Pollution ◽  
Heavy Pollution

Abstract. The study and control of air pollution involves measuring the structure of the atmospheric boundary layer (ABL) to understand the mechanisms of the interactions occurring between the atmospheric boundary layer and air pollution. Beijing, the capital of China, experienced heavy haze pollution in December 2016, and the city issued its first red-alert air pollution warning of the year (the highest PM2.5 concentrations were later found to exceed 450 µg m−3). In this paper, the vertical profiles of wind, temperature, humidity and the extinction coefficient (reflecting aerosol concentrations), as well as ABL heights and turbulence quantities under heavy haze pollution conditions, are analyzed, with data collected from lidar, wind profile radar (WPR), radiosondes, a 325 m meteorological tower (equipped with a 7-layer ultrasonic anemometer and 15-layer low-frequency wind, temperature, and humidity sensors) and ground observations. The ABL heights obtained by three different methods based on lidar extinction coefficient data (Hc) are compared with the heights calculated from radiosonde temperature data (Hθ), and their correlation coefficient can reach 72 %. Our results show that Hθ measured on heavy haze pollution days was generally lower than that measured on clean days without pollution, but Hc increased from clean to heavy pollution days. The time changes in friction velocity (u*) and turbulent kinetic energy (TKE) were clearly inversely correlated with PM2.5 concentration. Momentum and heat fluxes varied very little with altitude. The nocturnal sensible heat fluxes close to the Earth surface always stay positive. In the daytime of the haze pollution period, sensible heat fluxes were greatly reduced within 300 m of the ground. These findings will deepen our understanding of the boundary layer structure under heavy pollution conditions and improve the boundary layer parameterization in numerical models.

scholarly journals Dome effect of black carbon and its key influencing factors: a one-dimensional modelling study

2018 ◽  
Vol 18 (4) ◽  
pp. 2821-2834 ◽  
Author(s):  
Zilin Wang ◽  
Xin Huang ◽  
Aijun Ding
Keyword(s):  
Boundary Layer ◽  
Air Pollution ◽  
Black Carbon ◽  
Rural Areas ◽  
Land Surface ◽  
Critical Role ◽  
Aerosol Layer ◽  
Near Surface ◽  
Haze Pollution ◽  
The Impact

Abstract. Black carbon (BC) has been identified to play a critical role in aerosol–planetary boundary layer (PBL) interaction and further deterioration of near-surface air pollution in megacities, which has been referred to as the “dome effect”. However, the impacts of key factors that influence this effect, such as the vertical distribution and aging processes of BC, as well as the underlying land surface, have not been quantitatively explored yet. Here, based on available in situ measurements of meteorology and atmospheric aerosols together with the meteorology–chemistry online coupled model WRF-Chem, we conduct a set of parallel simulations to quantify the roles of these factors in influencing the BC dome effect and surface haze pollution. Furthermore, we discuss the main implications of the results to air pollution mitigation in China. We found that the impact of BC on the PBL is very sensitive to the altitude of aerosol layer. The upper-level BC, especially that near the capping inversion, is more essential in suppressing the PBL height and weakening the turbulent mixing. The dome effect of BC tends to be significantly intensified as BC mixed with scattering aerosols during winter haze events, resulting in a decrease in PBL height by more than 15 %. In addition, the dome effect is more substantial (up to 15 %) in rural areas than that in the urban areas with the same BC loading, indicating an unexpected regional impact of such an effect to air quality in countryside. This study indicates that China's regional air pollution would greatly benefit from BC emission reductions, especially those from elevated sources from chimneys and also domestic combustion in rural areas, through weakening the aerosol–boundary layer interactions that are triggered by BC.

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