Characterization of summer organic and inorganic aerosols in Beijing, China with an Aerosol Chemical Speciation Monitor

An Aerodyne Aerosol Chemical Speciation Monitor (ACSM) was first deployed in Beijing, China for characterization of summer organic and inorganic aerosols. The non-refractory submicron aerosol (NR-PM1) species, i.e., organics, sulfate, nitrate, ammonium, and chloride were measured in situ at a time resolution of ∼15 min from 26 June to 28 August, 2011. The total NR-PM1 measured by the ACSM agrees well with the PM2.5 measured by a Tapered Element Oscillating Microbalance (TEOM). The average total NR-PM1 mass for the entire study is 50 ± 30 μg m−3 with the organics being the major fraction, accounting for 40% on average. High concentration and mass fraction of nitrate were frequently observed in summer in Beijing, likely due to the high humidity and excess gaseous ammonia that facilitate the transformation of HNO3 to ammonium nitrate particles. Nitrate appears to play an important role in leading to the high particulate matter (PM) pollution since its contribution increases significantly as a function of aerosol mass loadings. Positive matrix factorization (PMF) of ACSM organic aerosol (OA) shows that the oxygenated OA (OOA) – a surrogate of secondary OA dominates OA composition throughout the day, on average accounting for 64%, while the hydrocarbon-like OA (HOA) shows a large increase at meal times due to the local cooking emissions. Our results suggest that high PM pollution in Beijing associated with stagnant conditions and southern air masses is characterized by the high contribution of secondary inorganic species and OOA from regional scale, whereas the aerosol particles during the clean events are mainly contributed by the local emissions with organics and HOA being the dominant contribution.