Fig. 3: Geographical origin of SOA categories.
From: Substantial contribution of transported emissions to organic aerosol in Beijing
a–d, Three-day back dispersion maps of air observed at the Beijing site (yellow star) in contact with the surface, coloured by component concentration observed at the site: solid-fuel SOA (a), aqueous SOA (b), aromatic-dominated SOA (c) and biogenic SOA (d). The average for the whole measurement period is shown. Areas contributing to above-average concentrations at the Beijing site are indicative of high emissions of the specific SOA precursors and shown in olive (below-average concentrations are shown in grey). Wintertime air masses from the Beijing–Tianjing–Hebei (BTH) region and from regions west of Beijing show high solid-fuel SOA concentrations. Aqueous SOA also associates largely with air from regions with high SO2 emissions, typically with very high relative humidity and thus high LWC. Summertime aromatic-dominated SOA shows regional origins from throughout the region south of Beijing, delimited roughly by a triangle defined by Beijing (yellow star), Xi’an (yellow square) and Shanghai (yellow circle). Summertime biogenic SOA also originates from the same direction but principally to the south of this region where biogenic emissions are largest.
