Abstract
The North China Plain (NCP) has been experiencing serious air quality problems since the rapid urbanization and industrialization and has been the subject of many studies over the years. This work presents mapping at a fine scale of the aerosol spatial and vertical variability obtained during the MOABAI campaign (Mobile Observation of Atmosphere By vehicle-borne Aerosol measurement Instruments) using a van equipped with a micro-pulse LIDAR, a sun photometer and in situ instruments, performing on-road measurements. The campaign was conducted from 5 May to 23 May 2017 and had as a main objective to map the pollutants distribution in Beijing and NCP area. A summary of aerosol properties during all measurement days and a comprehensive case study along the industrial Binhai New Area near Tianjin are presented. The highest AOD at 440 nm (1.34 and 1.9) were recorded during two heavy pollution episodes on 18 May and 19 May 2017, respectively. The lowest PBL (Planetary Boundary Layer) heights (< 1500 m) were recorded during the heavy pollution events, correlated with the highest AOD. Transport of dust from Gobi Desert was captured during the mobile measurements, impacting Beijing in the 9–13 May period. Exploring the NCP outside Beijing provided datasets in regions with lack of aerosol observation sites and allowed mapping higher aerosol concentrations when passing by polluted cities in NCP (Baoding, Tianjin and Tangshan). In this study, we provide the first mass concentration profiles derived from a mobile micro-pulse LIDAR, making use of complementary information on aerosol type from sun photometer and in situ data. The case study of 17 May 2017 revealed mean extinction coefficients of 0.14 ± 0.10 km−1 at 532 nm and total mass concentration of 80 ± 62 μg m−3 in the PBL (< 2000 m) for the mobile transect from Tianjin to Tangshan along the coast of Bohai Sea. The highest extinction (0.56 km−1) and mass concentrations (404 μg m−3) were found in the industrial Binhai New Area. The PM10 and PM2.5 fractions of the total mass concentration profiles were separated using the columnar size distribution derived from sun photometer measurements. A general good agreement was found between the lidar-derived PM concentrations at surface level and the ones recorded at the closest air quality stations along the transect, with the only exception along the industrial region near Tianjin port, where emissions were highly variable.
Highlights
The North China Plain (NCP) in north-eastern China is one of the most populated and polluted regions of China, where longstanding heavy aerosol pollution episodes frequently occur (Chen and Wang, 2015; Yang et al, 2018)
Both local and regional sources contribute to the air pollution in the NCP region, depending on the synoptic conditions, desert dust being advected over NCP when air flows are dominated by westerly winds (Sun et al, 2001) while fine particles pollution events occur with southern winds flow (Chen and Wang, 2015)
3.1 Overview of aerosol properties An overview of the aerosol optical properties is presented namely the aerosol optical depth (AOD) and Angstrom Exponent (AE) from PLASMA sun photometer and the Range Corrected Signals (RCS) and Planetary Boundary Layer (PBL) height from 185 lidar on-road measurements in NCP
Summary
The North China Plain (NCP) in north-eastern China is one of the most populated and polluted regions of China, where longstanding heavy aerosol pollution episodes frequently occur (Chen and Wang, 2015; Yang et al, 2018). Some of the most polluted cities in China (Beijing, Baoding, Tianjin, Tangshan, Shijiazhuang) are here and air pollution has become an important concern in this region (An et al, 2019; Sun et al, 2017; Zhu et al, 2016). Regional transport plays an important role in urban air pollution. Both local and regional sources contribute to the air pollution in the NCP region, depending on the synoptic conditions, desert dust being advected over NCP when air flows are dominated by westerly winds (Sun et al, 2001) while fine particles pollution events occur with southern winds flow (Chen and Wang, 2015). The measures taken through air pollution control policies show an improvement of air quality and a negative trend for PM2.5 concentrations since 2013
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