Long-term trends in fog and boundary layer characteristics in Tianjin, China--颗粒学报PARTICUOLOGY

Han, S., Cai, Z., Zhang, Y., Wang, J., Yao, Q., Li, P., & Li, X. (2015). Long-term trends in fog and boundary layer characteristics in Tianjin, China. Particuology, 20, 61–68. https://doi.org/10.1016/j.partic.2014.02.008

Long-term trends in fog and boundary layer characteristics in Tianjin, China

Suqin Han ^a *, Ziying Cai ^a, Yufen Zhang ^b *, Jiao Wang ^b, Qing Yao ^a, Peiyan Li ^a, Xiangjin Li ^a

a Tianjin Institute of Meteorological Science, Tianjin 300074, China
b State Environmental Protection Key Laboratory of Urban Ambient Air Particulate Matter Pollution Prevention and Control, College of Environmental Science and Engineering, Nankai University, Tianjin 300071, China

10.1016/j.partic.2014.02.008

Volume 20, June 2015, Pages 61-68

Received 30 August 2013, Revised 9 January 2014, Accepted 10 February 2014, Available online 27 May 2014.

E-mail: sq_han@126.com; zhafox@126.com; xiaozhimei01@163.com

Highlights

• Meteorological data were examined to determine the long-term trends of fog.

• Vertical structure of atmospheric boundary layer during fog events was analyzed.

• Variation characteristics of air pollutant concentrations during fog events were analyzed.

Abstract

Long-term trends in fog episodes, vertical variations of atmospheric boundary structure, and air pollutant concentrations during two different heavy fog events in the Tianjin area were analyzed. The total amount of fog has increased since 1980 due to the stability of the boundary layer and an increase of pollutant emissions. The variation in the characteristics of the boundary layer and air pollutant concentrations were significantly different between the two fog processes (fog I and fog II). The onset of fog I was accompanied by a temperature inversion in the low atmosphere, and the average kinetic energy showed a clear diurnal trend and vertical variation, which increased with height. The dissipation of fog I was mainly due to turbulence. However, the atmospheric stratification was not stable in the lower layer before the onset of fog II. The diurnal and vertical changes in kinetic energy were very small, in which turbulent momentum at each measurement height tended to be zero. In the dissipation process of fog II, wind speed increased significantly. Surface PM_2.5 concentrations decreased, but the ratio of PM_2.5 to PM₁₀ increased from 0.66 to 0.82 until fog I dissipated. However, the concentration of PM_2.5 did not decrease at the early stage of fog II, but the ratio of PM_2.5 to PM₁₀ PM_2.5/PM₁₀ decreased to 0.21 when fog II dissipated. This study showed that there was a clear difference in the evolution of pollutant concentration for different pollutants and in different developing stages during the fog events. PM_2.5 concentration accumulated faster than those of SO₂ and NO_x, and the PM_2.5 cumulative rate was greater in the mid-term of the fog process.

Graphical abstract

Keywords

Tianjin; Fog; Long-term trend; Boundary layer structure; Particulate matter; Air pollutant

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