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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 μg/m3 and 10.6 μg/m3, 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. • This study investigated the temporal variation of urban aerosol pollution island (UAPI) intensity using PM10 data from observation network and WRF-Chem. • PM10 concentrations was higher at night, but UAPI intensity was larger in the daytime. • Both colder days in winter and hotter days with heat wave in summer showed larger UAPI intensity. • UAPI was negatively correlated with urban heat island (UHI) in summer. • Mitigation of UHI strengthened UAPI by weakening turbulent mixing and decreasing urban boundary layer height. [ABSTRACT FROM AUTHOR]

Abstarct: Observations on a particulate matter (PM10 and PM2.5) were carried out during March 2015 to February 2017 over a high-altitude location Mahabaleshwar in the Western Ghats region in southwest India. Apart from temporal variation of PM and the ratio of PM2.5/PM10, impacts of local meteorological parameters on the concentration of PM are examined. PM10 showed a maximum concentration during pre-monsoon, whereas PM2.5 showed it in winter. The monsoon season showed the lowest concentrations for both PM10 and PM2.5. Concentrations were significantly reduced in 2016 due to the washout effect from enhanced rainfall during that year. Diurnal variations of PM were related to the variation in a planetary boundary layer, mountain valley winds as well as changes in different local sources. Dominance of primary particles was observed from the PM2.5/PM10 ratio. The Central Pollution Control Board (CPCB) threshold limit for PM was exceeded on several days mainly during pre-monsoon due to transported dust from the Arabian Peninsula and Thar Desert apart from an increase in the tourist activity. A typical case for transported dust event during March 2016 is studied. Organics and sulphate particles showed a significant enhancement during dust event. Overall, the study indicated emissions from mixed sources for PM from local as well as distant source regions over Mahabaleshwar. [ABSTRACT FROM AUTHOR]