Temporal variations of the contribution of combustion-derived water vapor to urban humidity during winter in Xi'an, China

Abstract

Combustion-derived water vapor (CDV) has significant impacts on urban climate and environment. However, temporal variations of contribution of CDV (CCDV) to urban humidity are unclear due to lack of observations. This study examined the temporal variations of CCDV in Xi'an during winter from 2016 to 2019. We found that the diurnal variation of CCDV is mainly controlled by atmospheric stability, but the peak of CCDV at 9 am is due to the increasing water vapor emission by motor vehicles during the morning rush hour. In addition, the monthly variation of CCDV is related to fossil fuel consumption, but the low values of CCDV in late January and early February is due to substantial decrease of energy utility because of the massive outflow of population during the Spring Festival. Our findings may be helpful for urban pollution control because CDV can play an important role in the secondary conversion of pollutants.