Temporal characteristics of greenhouse gases (CO2 and CH4) in the megacity Shanghai, China: Association with air pollutants and meteorological conditions

Abstract

CO 2 and CH 4 are the two most potent greenhouse gases (GHGs) in the atmosphere. They are frequently monitored at background observatories, but less so in urban areas, especially in China. In this study, the temporal variations of urban atmospheric CO 2 and CH 4 , including seasonal, weekly, and diurnal characteristics, were obtained based on one year of continuous measurement in the megacity Shanghai. Probable anthropogenic sources were further investigated through relationships among GHGs and atmospheric pollutants. Potential sources regions and transport pathways of GHGs were studied in association with meteorological conditions. The annual average concentrations of CO 2 and CH 4 were 428.36 ± 13.96 ppm and 2154 ± 190 ppb, respectively, which were higher than those at global and regional background observatories. The highest CO 2 concentration appeared in winter and the lowest in autumn, whereas CH 4 values were highest in summer and lowest in spring. Both CO 2 and CH 4 showed strong diurnal variations, but only CO 2 exhibited seasonal and weekly differences due to the variation of emission sources and plant photosynthesis in Shanghai and the surrounding Yangtze River Delta (YRD). CO 2 and combustion-derived air pollutants were co-emitted from similar sources and co-transported to the research site, as demonstrated by correlation analysis. Furthermore, the correlation analysis also suggested some neglected anthropogenic combustion sources of CH 4 in Shanghai, besides the traditional biogenic emissions from landfills, wetlands, paddy fields, and dairy farms. The anthropogenic CO 2 concentration in urban Shanghai estimated from a CO 2 -CO regression model was 14.98 ± 5.09 ppm, together with a background concentration of 413.31 ± 7.07 ppm, which was higher than at global background sites but lower than at the nearby regional background Lin'an station. GHGs were accumulated from local sources under stable weather conditions and transported from remote sources at high wind speeds. Air masses from “super-emitters” north and south of the observation site contributed most of the elevation in GHGs concentration above their annual averages. Considering the co-emissions of GHGs and air pollutants from carbon-containing material combustion and use, and the potential of methane to generate O 3 in the urban environment, reduction of CO 2 and CH 4 together with air pollutants could benefit both climate and air quality in Shanghai and the surrounding YRD. • CO 2 and CH 4 were measured together with air pollutants and meteorological conditions in urban Shanghai. • Both CO 2 and CH 4 showed diurnal variations, but only CO 2 showed seasonal and weekday effects. • Anthropogenic sources affected the elevated concentrations of GHGs in urban environment. • GHGs were accumulated from local sources in stable, together with transport from remote sources. • Joint control of GHGs and air pollutants could benefit both climate and air quality.