Vertically decreased VOC concentration and reactivity in the planetary boundary layer in winter over the North China Plain

Abstract

Abstract The vertical structure of volatile organic compounds (VOCs) is important to understanding the formation mechanisms of O3 and secondary organic aerosol (SOA). To explore the vertical evolution characteristics of VOCs, an observational field campaign using a tethered balloon was carried out in Yuanshi County, Shijiazhuang, from January 8 to 16, 2019. Meteorological variables of the planetary boundary layer (PBL) were measured, and 83 VOC samples were collected. The concentrations of 87 compounds and a total of 10 vertical profiles were obtained. The VOC concentration gradually decreased from the surface to 1000 m, decreasing by 34.8% from the surface to 400 m and 11.4% from 400 m to 1000 m. The proportion of alkanes increased from 60.2% to 79.0%; the proportions of alkenes, halohydrocarbons, and acetylene decreased from 11.8%, 12.3%, and 4.2% to 4.5%, 2.8%, and 1.8%, respectively; and the proportion of aromatics changed very little. The vertical evolution of VOCs had responses to different meteorological conditions in the PBL. The concentration decreased slower in a strong convection state than in a stable state. The VOC concentration at night was higher in the stable boundary layer (SBL) (235 ± 135 ppbv) than in the residual layer (RL) (181 ± 135 ppbv). The concentration and NO3 loss rate of alkenes decreased in the RL at night, implying that the nighttime SOA formation potential may be weaker in the RL.