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Abstract. An intensive field measurement was conducted at a remote, background,high-altitude site (Qomolangma Station, QOMS, 4276 m a.s.l.) in thenorthern Himalayas, using an Aerodyne high-resolution time-of-flight aerosolmass spectrometer (HR-ToF-AMS) along with other collocated instruments. Thefield measurement was performed from 12 April to 12 May 2016 to chemicallycharacterize the high time-resolved submicron particulate matter (PM 1 )and obtain the dynamic processes (emissions, transport, and chemicalevolution) of biomass burning (BB), frequently transported from South Asia tothe Himalayas during pre-monsoon season. Overall, the average( ± 1 σ ) PM 1 mass concentration was4.44 ( ± 4.54)  µ g m −3 for the entire study, which is comparable withthose observed at other remote sites worldwide. Organic aerosol (OA) was thedominant PM 1 species (accounting for 54.3 % of total PM 1 onaverage) followed by black carbon (BC) (25.0 %), sulfate (9.3 %),ammonium (5.8 %), nitrate (5.1 %), and chloride (0.4 %). The averagesize distributions of PM 1 species all peaked at an overlappingaccumulation mode ( ∼  500 nm), suggesting that aerosol particles wereinternally well-mixed and aged during long-range transport. Positive matrixfactorization (PMF) analysis on the high-resolution organic mass spectraidentified three distinct OA factors, including a BB-related OA (BBOA,43.7 %), a nitrogen-containing OA (NOA, 13.9 %) and a more-oxidizedoxygenated OA (MO-OOA, 42.4 %). Two polluted episodes with enhancedPM 1 mass loadings and elevated BBOA contributions from the west andsouthwest of QOMS during the study were observed. A typical BB plume wasinvestigated in detail to illustrate the chemical evolution of aerosolcharacteristics under distinct air mass origins, meteorological conditions,and atmospheric oxidation processes.

Chemical characterization of long-range transport biomass burning emissions to the Himalayas: insights from high-resolution aerosol mass spectrometry