Effect of Long-Range Transported Aerosol on Urban Air Quality in Eastern Germany

Submicron particles (PM₁) play a crucial role in air quality and human health. This study investigates the influence of long-range transport (LRT) on urban aerosol levels in Leipzig, Germany, using high-resolution aerosol mass spectrometry measurements at two sites: an urban traffic site (Eisenbahnstrasse, Eiba) and a rural background site (Melpitz), located ∼50 km apart. The sites were analyzed during winter 2017 under two dominant wind regimes: East and West. These sites were directly linked to each other, which was supported by cross-correlation analysis, with a typical time lag of -2 h in East and +4 h in West. Eastern winds brought higher concentrations (Melpitz: 35.50 μg m^-3, Eiba: 37.47 μg m^-3), while Western winds led to cleaner conditions. After being corrected for time lag, the Urban Increment (UI) was estimated, showing that during Eastern wind, only ∼9% of PM₁ mass measured at Eiba was attributed to urban sources, highlighting the dominant contribution of regionally transported aerosol. Furthermore, source apportionment of organic aerosol (OA) identified five major factorsthree primary OA and two oxygenated OAat both sites. The findings underscore the significant role of regional pollution in shaping urban air quality and the need for cross-border emission reduction strategies.