Temporal variation of urban aerosol pollution island and its relationship with urban heat island

Although urban aerosols have been extensively explored, the variation of aerosols across space and time in the city and its underlying mechanism have not been quantitatively understood. This study defined the phenomenon of higher aerosols concentrations in the urban areas than in the surrounding rural areas as Urban Aerosol Pollution Island (UAPI) and quantified UAPI intensity using the urban-rural difference of Particulate Matter (PM10) concentrations. We investigated the diurnal and seasonal variations of UAPI and its relationship with Urban Heat Island (UHI) in the metropolitan area of Berlin using the combination of a long-term (2010-2017) observation network and the WRF-Chem model. Observation data showed that UAPI existed at most of time, with more than one-quarter of the days showing daily mean UAPI intensity of more than 5 mu g/m(3) and 10.6 mu g/m(3), respectively at background and traffic stations. The PM10 concentrations and UAPI intensity at background stations showed opposite diurnal variations, with higher PM10 concentrations at night, but larger UAPI intensity in the daytime. Seasonally, both PM10 concentrations and UAPI showed larger values in winter. The seasonal variation of UAPI intensity was closely related to the air temperature. The colder days in winter and hotter days with heat wave in summer showed larger UAPI intensity. The UAPI was negatively correlated to UHI in summer. The mitigation of UHI increased PM10 concentrations in urban areas by -3%, leading to a stronger UAPI. This study can contribute to the accurate risk assessment of aerosol pollution and the design of mitigation strategies.