Spatio-Temporal Characteristics of Air Quality Index (AQI) over Northwest China

Shah Zaib,Muhammad Bilal,Jianjiang Lu

doi:10.3390/atmos13030375

Abstract

In recent years, air pollution has become a serious threat, causing adverse health effects and millions of premature deaths in China. This study examines the spatial-temporal characteristics of ambient air quality in five provinces (Shaanxi (SN), Xinjiang (XJ), Gansu (GS), Ningxia (NX), and Qinghai (QH)) of northwest China (NWC) from January 2015 to December 2018. For this purpose, surface-level aerosol pollutants, including particulate matter (PMx, x = 2.5 and 10) and gaseous pollutants (sulfur dioxide (SO2), nitrogen dioxide (NO2), carbon monoxide (CO), and ozone (O3)) were obtained from China National Environmental Monitoring Center (CNEMC). The results showed that fine particulate matter (PM2.5), coarse particulate matter (PM10), SO2, NO2, and CO decreased by 28.2%, 32.7%, 41.9%, 6.2%, and 27.3%, respectively, while O3 increased by 3.96% in NWC during 2018 as compared with 2015. The particulate matter (PM2.5 and PM10) levels exceeded the Chinese Ambient Air Quality Standards (CAAQS) Grade II standards as well as the WHO recommended Air Quality Guidelines, while SO2 and NO2 complied with the CAAQS Grade II standards in NWC. In addition, the average air quality index (AQI), calculated from ground-based data, improved by 21.3%, the proportion of air quality Class I (0–50) improved by 114.1%, and the number of pollution days decreased by 61.8% in NWC. All the pollutants’ (except ozone) AQI and PM2.5/PM10 ratios showed the highest pollution levels in winter and lowest in summer. AQI was strongly positively correlated with PM2.5, PM10, SO2, NO2, and CO, while negatively correlated with O3. PM10 was the primary pollutant, followed by O3, PM2.5, NO2, CO, and SO2, with different spatial and temporal variations. The proportion of days with PM2.5, PM10, SO2, and CO as the primary pollutants decreased but increased for NO2 and O3. This study provides useful information and a valuable reference for future research on air quality in northwest China.

Highlights

Unprecedented economic activity, urbanization, industrialization, and motorization have deteriorated the ambient air quality in China [1,2,3,4,5,6]
PM2.5 and PM10 failed to comply with Chinese Ambient Air Quality Standards (CAAQS) Grade II standards in SN, XJ, GS, NX, and northwest China (NWC) (Figure 1a,b), while SO2 and NO2 complied with CAAQS Grade II standards (60 μg/m3 and 40 μg/m3, annual mean) in SN, XJ, GS, NX, QH, and NWC (Figure 1c,d)
carbon monoxide (CO) and O3 do not have annual standards under CAAQS; CO decreased in SN, XJ, GS, NX, QH, and NWC, while O3 decreased in GS and QH during 2018 as compared with 2015 (Figure 1e,f)

Summary

Introduction

Unprecedented economic activity, urbanization, industrialization, and motorization have deteriorated the ambient air quality in China [1,2,3,4,5,6]. Several studies have reported higher pollution levels in NWC due to increased industry, coal consumption, distinct topography, and adverse meteorology [2,5,7,8,9,10,11]. Increased pollution levels have attracted the attention of the general public, the scientific community, and relevant authorities because of their detrimental health effects [4,12,13,14,15,16]. Even after strict environmental regulations, the air pollution in some areas of NWC is beyond certain limits and causes serious health effects [25,26,27,28]

Methods

Results

Discussion

Conclusion