Water-Soluble Ions in Atmospheric Aerosol Measured in a Semi-Arid and Chemical-Industrialized City, Northwest China

Huimin Jiang,Fanglong Wang,Feiteng Wang,Zhongqin Li,Shan Ma,Xin Zhang,Xi Zhou

doi:10.3390/atmos12040456

Abstract

We investigated water-soluble ions (WSIs) of aerosol samples collected from 2016 to 2017 in Lanzhou, a typical semi-arid and chemical-industrialized city in Northwest China. WSIs concentration was higher in the heating period (35.68 ± 19.17 μg/m3) and lower in the non-heating period (12.45 ± 4.21 μg/m3). NO3−, SO42−, NH4+ and Ca2+ were dominant WSIs. The concentration of SO42− has decreased in recent years, while the NO3− level was increasing. WSIs concentration was affected by meteorological factors. The sulfur oxidation and nitrogen oxidation ratios (SOR and NOR) exceeded 0.1, inferring the vital contribution of secondary transformation. Meanwhile higher O3 concentration and temperature promoted the homogeneous reaction of SO2. Lower temperature and high relative humidity (RH) were more suitable for heterogeneous reactions of NO2. Three-phase cluster analysis illustrated that the anthropogenic source ions and natural source ions were dominant WSIs during the heating and non-heating periods, respectively. The backward trajectory analysis and the potential source contribution function model indicated that Lanzhou was strongly influenced by the Hexi Corridor, northeastern Qinghai–Tibetan Plateau, northern Qinghai province, Inner Mongolia Plateau and its surrounding cities. This research will improve our understanding of the air quality and pollutant sources in the industrial environment.

Highlights

Due to rapid urbanization processes and industrialization development, aerosols have drawn much attention from the government, the public, and scientists
The rank of ion concentrations measured in the heating period was: NO3− (12.20 ± 9.69 μg/m3) > SO42− (6.83 ± 3.47 μg/m3) > Ca2+ (6.82 ± 2.93 μg/m3) > NH4+ (5.84 ± 2.77 μg/m3) > Cl− (2.11 ± 1.12 μg/m3) > Na+ (0.84 ± 0.34 μg/m3) > K+ (0.65 ± 0.35 μg/m3) > Mg2+ (0.39 ± 0.14 μg/m3), which indicated that NO3−, Ca2+, SO42− and NH4+ were the main water-soluble ions (WSIs) in Lanzhou, accounting for 88.81% of WSIs
The rank of ion concentrations measured in the non-heating period was: Ca2+ (4.37 ± 2.20 μg/m3) > SO42− (3.27 ± 1.20 μg/m3) > NO3− (2.41 ± 1.48 μg/m3) > NH4+ (1.04 ± 0.72 μg/m3) > Cl− (0.51 ± 0.23 μg/m3) > Na+ (0.41 ± 0.50 μg/m3) > K+ (0.24 ± 0.10 μg/m3) > Mg2+ (0.21 ± 0.11 μg/m3)

Summary

Introduction

Due to rapid urbanization processes and industrialization development, aerosols have drawn much attention from the government, the public, and scientists. Water-soluble ions (WSIs) are essential components of aerosols, which include sulfate (SO42−), nitrate (NO3−), ammonium (NH4+) and alkali cations. They can contribute to 60–70% of the total suspended particles (TSP) [4]. For the past few years, China’s air quality has been much lower than that of other countries, which has remained in the spotlight in many cities in China, like Xi’an, Shanghai, Dalian, Beijing and other developed cities and studies have been conducted to characterize WSIs and their contribution to TSP [14,15,16,17]

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