Insights into the compositional differences of PM1 and PM2.5 from aerosol mass spectrometer measurements in Beijing, China

This is the authors' abstract. We don't add key points for this paper.

Aerosol mass spectrometers (AMS) have been widely used for characterization of submicron aerosol (PM 1 ) species in the world. However, the chemical differences between PM 1 and fine particles (PM 2.5 ) in megacities are poorly understood. Here a PM 1 high-resolution AMS with standard vaporizer (SV) and a PM 2.5 time-of-flight aerosol chemical speciation monitor (ToF-ACSM) with capture vaporizer (CV) were deployed simultaneously in summer and winter in Beijing, China, and the chemical differences of non-refractory aerosol species between PM 1 and PM 2.5 were characterized. Our results showed that aerosol species in PM 2.5 were overall highly correlated with those in PM 1 ( r 2 > 0.8), yet the PM 1 /PM 2.5 ratios varied largely for different aerosol species. Nitrate existed dominantly in PM 1 (80–90%), while a considerable fraction of sulfate (30–45%) was observed in the range of 1–2.5 μm (PM 1–2.5 ). Comparatively, PM 1 organics showed higher fractions in PM 2.5 in summer than winter (∼70%). The changes in PM 1 /PM 2.5 ratios of secondary inorganic aerosol (SIA) depended strongly on relative humidity (RH) in summer with considerable decreases as the increase of RH, while such a RH dependence of PM 1 /PM 2.5 ratios was not significant in winter due to the absence of high RH data. We further compared the source apportionment results of organic aerosol (OA) between PM 1 and PM 2.5 . Similar to previous studies, the SV AMS reported ubiquitously higher primary OA than the CV ToF-ACSM, nearly by a factor of 2 for cooking OA, and the difference in secondary OA composition can be substantial, particularly in winter. With the simultaneous measurements of AMS and ACSM, a parameterized relationship between oxygen-to-carbon (O/C) ratio and CV f 44 (fraction of m/z 44 in OA) in summer and winter was developed, which has a potential implication for studying the oxidation and hygroscopicity properties of OA considering the rapid increases in CV ToF-ACSM measurements worldwide.