Abstract
Particle size distribution, water soluble ions, and black carbon (BC) concentration in a long-term haze-fog episode were measured using a wide-range particle spectrometer (WPS), a monitor for aerosols and gases (MARGA), and an aethalometer (AE33) in Nanjing from 16 to 27 November, 2018. The observation included five processes of clean, mist, mix, haze, and fog. Combined with meteorological elements, the HYSPLIT model, and the IMPROVE model, we analyzed the particle size distribution, chemical composition, and optical properties of aerosols in different processes. The particle number size distribution (PNSD) in five processes differed: It was bimodal in mist and fog and unimodal in clean, mix, and haze. The particle surface area size distribution (PSSD) in different processes showed a bimodal distribution, and the second peak of the mix and fog processes shifted to a larger particle size at 480 nm. The dominant air masses in five processes differed and primarily originated in the northeast direction in the clean process and the southeast direction in the haze process. In the mist, mix, and fog processes local air masses dominated. NO3− was the primary component of water soluble ions, with the lowest proportion of 45.6% in the clean process and the highest proportion of 53.0% in the mix process. The ratio of NH4+ in the different processes was stable at approximately 23%. The ratio of SO42− in the clean process was 26.2%, and the ratio of other processes was approximately 20%. The average concentration of BC in the fog processes was 10,119 ng·m−3, which was 3.55, 1.80, 1.60, and 1.46 times that in the processes of clean, mist, mix, and haze, respectively. In the different processes, BC was primarily based on liquid fuel combustion. NO3−, SO42−, and BC were the main contributors to the atmospheric extinction coefficient and contributed more than 90% in different processes. NO3− contributed 398.43 Mm−1 in the mix process, and SO42− and BC contributed 167.90 Mm−1 and 101.19 Mm−1, respectively, during the fog process.
Highlights
Anthropogenic aerosols include nitrates, sulfates, ammonium salts, black carbon, organic matter, and dust [1,2]
The distribution characteristics of pollutants in the processes of clean, mist, haze, mix, and fog during the haze-fog episode in Nanjing were discussed by using high-resolution online observation instruments
The particle number size distribution (PNSD) was variable in different processes and bimodal in the processes of mist and fog, and the particle sizes at peak were 30 nm, 87 nm, 36 nm, and 87 nm
Summary
Anthropogenic aerosols include nitrates, sulfates, ammonium salts, black carbon, organic matter, and dust [1,2]. Aerosol particles can accumulate and cause air pollution in unfavorable dispersion conditions, and produce adverse effects on human health and atmospheric visibility [6,7,8]. Haze is an atmospheric phenomenon in which the sky clarity is obscured by a large number of fine dry particles, during which the atmospheric visibility and relative humidity (RH) are usually less than 5 km and 80% [9,10]. When more water vapor exists in the air, some dry aerosol particles with strong water absorption will develop and eventually be activated into the CCN [11,12], which produces a larger quantity of fog droplets with a smaller size, which further reduce the visibility. The haze problem in the central and eastern regions of China has become increasingly significant in the past two or three decades [14,15,16,17,18], which is attributed to the significant increase in atmospheric aerosols emitted by humans [19,20]
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