Observations of the atmospheric boundary layer structure 
over Beijing urban area during air pollution episodes

Wang, Linlin; Liu, Junkai; Gao, Zhiqiu; Li, Yubin; Huang, Meng; Fan, Shuai; Zhang, Xiaoye; Yang, Yibo; Miao, Shiguang; Zhao, Han; Sun, Yele; Chen, Yong; Yang, Tao

doi:10.5194/acp-2018-1184

Cited by 3 publications

(2 citation statements)

References 45 publications

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“…In North China, PM pollution is generally accompanied by an increase in water vapor (Wang et al, 2019;Zhou et al, 2014). Our study also shows that the specific humidity is well correlated with PM 2.5 , especially in the winter and summer (Figure 8).…”

Section: Effects Of Water Vapor and Pm On Dlrsupporting

confidence: 68%

Observed Relationships Between the Urban Heat Island, Urban Pollution Island, and Downward Longwave Radiation in the Beijing Area

Ju¹,

Zhou

Lenschow

et al. 2020

Earth and Space Science

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We used the mean air temperature and particulate matter concentration at northern and southern rural stations as rural background values to calculate the urban heat island intensity (UHII) and urban pollution island intensity (UPII) for Beijing. The correlation between UHII and UPII is significantly negative in winter during the daytime and nighttime when selecting southern rural background stations but significantly positive in spring during both daytime and nighttime and in winter during the nighttime when selecting northern rural background stations. The downward longwave radiation (DLR) is highly correlated with surface air temperature and water vapor, and with particulate matter concentration in winter and summer. Water vapor also has a high correlation with particulate matter concentration in winter and summer. Winter data were used to investigate the particulate matter contribution to DLR to minimize the effect of humidity. The results indicate that in winter the urban area DLR and net radiation increased more than rural area under polluted conditions compared with clean conditions, which may lead to an increase in UHII. But in other seasons with more moisture, the aerosol effect on DLR is smaller than water vapor. Our results imply that the contribution of air pollutants to DLR had been overestimated in recent studies without removing water vapor effects on the longwave radiation. We suggest that the interaction between the urban heat island and the urban pollution island and related mitigation strategies needs to be carefully studied in the future by considering different climate zone and seasons.On the other hand, a UPI can increase aerosol radiative forcing in an urban area. The downward longwave radiation (DLR) was found to be greater at urban sites, which have more polluted air (

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Section: Effects Of Water Vapor and Pm On Dlrsupporting

confidence: 68%

Observed Relationships Between the Urban Heat Island, Urban Pollution Island, and Downward Longwave Radiation in the Beijing Area

Ju¹,

Zhou

Lenschow

et al. 2020

Earth and Space Science

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“…Cloud cover is one of the strongest atmospheric constituents and thus act as a strongest modulator of solar radiation energy i.e., absorbed by earth atmospheric systems and causes profound effects on DSR. Wang et al ( 2019 ) reported maximum attenuation of DSR with attenuation ratio of 7.4% at 1200 LST. These attenuation differences are expected due to degree of pollution, solar angle differences, cloud cover and pollutant components etc.…”

Section: Resultsmentioning

confidence: 99%

Changes in tropospheric ozone concentration over Indo-Gangetic Plains: the role of meteorological parameters

Payra

Gupta

Sarkar

et al. 2022

Meteorol Atmos Phys

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This study seeks to understand and quantify the changes in tropospheric ozone (O 3 ) in lower troposphere (LT), middle troposphere (MT) and upper middle troposphere (UMT) over the Indo-Gangetic Plains (IGPs), India during the COVID-19 lockdown 2020 with that of pre-lockdown 2019. The gridded datasets of ozone from the European Centre for Medium-range Weather Forecasts (ECMWF) reanalysis product, ERA5 in combination with statistical interpolated (IDWs) surface NO 2 observations, present a consistent picture and indicate a significant tropospheric ozone enhancement over IGP during COVID-19 lockdown restrictions in May 2020. The Paper also examines the influencing role of meteorological parameters on increasing ozone concentration. Over LT, an increase in O 3 concentration (23%) is observed and in MT to UMT an enhancement of about 9–18% in O 3 concentration have been seen during May 2020 with respect to May 2019. An investigation on causes of increasing ozone concentration (35–85 ppbv) from MT to UMT during May 2020 reveals that there was significant rise (by 1–6%) in low cloud cover (LCC). Notably, higher LCC increases the backscattering of upward solar radiation from the top of the atmosphere. A positive difference of 5–25 W/m 2 in upward solar radiation (USR) is observed across the entire study region. The result suggests that higher LCC significantly contributed to the enhanced USR. Thereby, resulting in higher photolysis rate that lead to an increase in mid tropospheric ozone concentration during May 2020. The results highlight the importance of LCC as an important pathway in ozone formation and aid in scientific understanding of it.

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Vertical observations of the atmospheric boundary layer structure over Beijing urban area during air pollution episodes

et al. 2019

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Abstract. We investigated the interactions between the air pollutants and the structure of the urban boundary layer (UBL) over Beijing by using the data mainly obtained from the 325 m meteorological tower and a Doppler wind lidar during 1–4 December 2016. Results showed that the pollution episodes in this period could be characterized by low surface pressure, high relative humidity, weak wind, and temperature inversion. Compared with a clean daytime episode that took place on 1 December, results also showed that the attenuation ratio of downward shortwave radiation was about 5 %, 24 % and 63 % in afternoon hours (from 12:00 to 14:00 local standard time, LST) on 2–4 December, respectively, while for the net radiation (Rn) attenuation ratio at the 140 m level of the 325 m tower was 3 %, 27 % and 68 %. The large reduction in Rn on 4 December was not only the result of the aerosols, but also clouds. Based on analysis of the surface energy balance at the 140 m level, we found that the sensible heat flux was remarkably diminished during daytime on polluted days and even negative after sunrise (about 07:20 LST) till 14:00 LST on 4 December. We also found that heat storage in the urban surface layer played an important role in the exchange of the sensible heat flux. Owing to the advantages of the wind lidar having superior spatial and temporal resolution, the vertical velocity variance could capture the evolution of the UBL well. It clearly showed that vertical mixing was negatively related to the concentrating of pollutants, and that vertical mixing would also be weakened by a certain quantity of pollutants, and then in turn worsened the pollution further. Compared to the clean daytime on 1 December, the maximums of the boundary layer height (BLH) decreased about 44 % and 56 % on 2–3 December, when the average PM2.5 (PM1) concentrations in afternoon hours (from 12:00 to 14:00 LST) were 44 (48) µg m−3 and 150 (120) µg m−3. Part of these reductions of the BLH was also contributed by the effect of the heat storage in the urban canopy.

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Observations of the atmospheric boundary layer structure over Beijing urban area during air pollution episodes

Cited by 3 publications

References 45 publications

Observed Relationships Between the Urban Heat Island, Urban Pollution Island, and Downward Longwave Radiation in the Beijing Area

Observed Relationships Between the Urban Heat Island, Urban Pollution Island, and Downward Longwave Radiation in the Beijing Area

Changes in tropospheric ozone concentration over Indo-Gangetic Plains: the role of meteorological parameters

Vertical observations of the atmospheric boundary layer structure over Beijing urban area during air pollution episodes

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