Abstract. This study presents the source apportionment of PM2.5 performed by positive matrix factorization (PMF) on data presented here which were collected at urban (Institute of Atmospheric Physics – IAP) and rural (Pinggu – PG) sites in Beijing as part of the Atmospheric Pollution and Human Health in a Chinese megacity (APHH-Beijing) field campaigns. The
campaigns were carried out from 9 November to 11 December 2016
and from 22 May to 24 June 2017. The PMF analysis included both organic and inorganic species, and a seven-factor output provided the most reasonable solution for the PM2.5 source apportionment. These factors are
interpreted as traffic emissions, biomass burning, road dust, soil dust, coal combustion, oil combustion, and secondary inorganics. Major contributors
to PM2.5 mass were secondary inorganics (IAP: 22 %; PG: 24 %),
biomass burning (IAP: 36 %; PG: 30 %), and coal combustion (IAP: 20 %;
PG: 21 %) sources during the winter period at both sites. Secondary
inorganics (48 %), road dust (20 %), and coal combustion (17 %) showed the highest contribution during summer at PG, while PM2.5 particles
were mainly composed of soil dust (35 %) and secondary inorganics (40 %)
at IAP. Despite this, factors that were resolved based on metal signatures
were not fully resolved and indicate a mixing of two or more sources. PMF
results were also compared with sources resolved from another receptor model
(i.e. chemical mass balance – CMB) and PMF performed on other measurements (i.e. online and offline aerosol mass spectrometry, AMS) and showed good agreement for some but not all sources. The biomass burning factor in PMF may contain aged aerosols
as a good correlation was observed between biomass burning and oxygenated
fractions (r2= 0.6–0.7) from AMS. The PMF failed to resolve some sources identified by the CMB and AMS and appears to overestimate the dust sources. A comparison with earlier PMF source apportionment studies from the
Beijing area highlights the very divergent findings from application of this
method.