Temporal characteristics of carbon dioxide and ozone over a rural-cropland area in the Yangtze River Delta of eastern China

Abstract

In this study, rural atmospheric carbon dioxide (CO2) and ozone (O3) were measured from January 2015 to December 2018 to investigate characteristics of greenhouse gases in eastern China. Results showed that the annual average CO2 (O3) concentration in 2018 decreased by 2% (increased by 19%) when compared with that in 2015. CO2 concentrations exhibited monthly variability, peaking in February (443.7 ppm) and reaching their lowest levels in July (363.0 ppm); whereas, monthly O3 showed a bimodal pattern with peaks in June (51.3 ppb) and September (34.5 ppb). Regarding the diurnal variation, the maximum CO2 (O3) concentration occurred at nighttime (in the daytime) and a minimum CO2 (O3) in the daytime (at nighttime). As demonstrated by correlation analysis, CO2 and O3 variations were partly modulated by NOx and PM2.5. Furthermore, CO2 showed significant positive correlations with relative humidity in winter, while O3 showed strong positive correlations with temperature in spring. CO2 was accumulated from local sources under calm conditions (< 2 m s−1) and derived from remote sources at high wind speeds (> 4 m s−1), while O3 concentrations were peaking at medium wind speeds of 2–4 m s−1. CO2 was found to derive from long-distance (short-distance transport) transport in spring (the other three seasons), whereas O3 is mainly from long-distance (short-distance) transport in winter (the other three seasons). This work sheds light on the temporal characteristics of CO2 and O3, which has important implications for implementing practices to mitigate source emissions over cropland areas.