Spatiotemporal variations of tropospheric NO2 in Lanzhou for the period 2009–2018 based on satellite remote sensing

Abstract

Air quality has been associated with human health and with issues related to the climate, water, agriculture, and the economy across the world. NO2 is one of the main pollutants in the atmosphere; therefore, it is essential to analyze the quantitative changes and spatial distribution of NO2. The spatiotemporal changes in the vertical column densities and related influencing factors of tropospheric NO2 over Lanzhou for the period 2009–2018 were analyzed using remote sensing inversion data from the Ozone Monitoring Instrument and methods such as coefficient of variation, trend analysis, Hurst index, and risk analysis of NO2 population exposure. Results indicate that the concentration of the tropospheric NO2 column shows an overall upward trend from 2009 to 2018, and that the four-year mean distribution of seasonal tropospheric NO2 vertical column densities is winter > autumn > spring > summer. A combination of topographic characteristics and an analysis of meteorological factors aid the NO2 column in Lanzhou to be “high in winter and low in summer” and the analysis of socioeconomic factors reveals that car ownership makes a marked contribution to the concentration of the NO2 column in Lanzhou. Furthermore, the coefficient of variation, trend analysis, Hurst index, and NO2 population exposure risk analysis suggests that, in the Lanzhou area, overall NO2 concentrations are relatively stable, with a small fluctuation range and slow growth trend. Future projections show the vertical NO2 column densities in the research area undergoing a downward trend while the population density remains high.