Chemical Differences Between PM₁ and PM_2.5 in Highly Polluted Environment and Implications in Air Pollution Studies

Abstract

Submicron aerosol (PM1) species measured by aerosol mass spectrometers have been widely used to validate chemical transport models; however, the uncertainties due to chemical differences between PM1 and PM2.5 are poorly constrained. Here we characterized such differences in a highly polluted environment in north China in winter. Our results showed that the changes in PM1/PM2.5 ratios as a function of relative humidity (RH) were largely different for primary and secondary species. Secondary organic and inorganic aerosol (SOA and SIA) presented clear decreases in PM1/PM2.5 ratios at RH > 60% during periods with high SIA contributions (>50%), likely driven by the changes in aerosol hygroscopicity and phase states, while the traffic and coal combustion OA had limited dependence on RH. Thermodynamic modeling showed negligible impacts of PM differences on predictions of particle acidity, yet these impacts can cause a difference in aerosol water content by up to 50–70%.

An inter-laboratory comparison of aerosol in organic ion measurements by Ion Chromatography: implications for aerosol pH estimate

“…It should be noted that higher SO4 2concentrations in online ACSM data could potentially be due to ACSM not being able to separate organosulfate from sulfate. ACSM-NO3 -, -SO4 2and -NH4 + were also reported to be higher (approximately 10-20%) than filter analysis based NO3 -, SO4 2and NH4 + in another study (Sun et al, 2020). Although the comparison between IC and ACSM provided important information about the data from the two methods, we recognize that we only have 8 data points here.…”

“…aerodynamic lens was also deployed on the same roof of the building at IAP for real-time measurements of non-refractory (NR) chemical species (Organics, Cl -, NO3 -, SO4 2and NH4 + ) in PM2.5 (NR-PM2.5) with 2 min time resolution (Sun et al, 2020). Another ToF-ACSM was also used https://doi.org/10.5194/amt-2020-156 Preprint.…”

An evaluation of source apportionment of fine OC and PM2.5by multiple methods: APHH-Beijing campaigns as a case study

“…SNA in AMS data was much higher than measured SNA during winter, but lower than that in summer at IAP. Differences were also found in online ACSM and filter-based SNA concentrations in another study 54 . Possible reasons could be the uncertainties of SNA in ACSM analysis 55 ; and evaporation of ammonium nitrate and the difficulties in separating organosulfate from sulfate in AMS 56 .…”

An interlaboratory comparison of aerosol inorganic ion measurements by ion chromatography: implications for aerosol pH estimate

“…An Aerodyne time-of-flight aerosol chemical speciation monitor (ToF-ACSM) with a PM 2.5 aerodynamic lens was also deployed on the same roof of the building at IAP for real-time measurements of nonrefractory (NR) chemical species (organics, Cl − , NO − 3 , SO 2− 4 and NH + 4 ) in PM 2.5 (NR-PM 2.5 ) with a 2 min time resolution (Sun et al, 2020). Another ToF-ACSM was also used to measure the PM 2.5associated nonrefractory chemical species at the Beijing University of Chemical Technology (BUCT), which is located at the West 3rd Ring Road of Beijing and approximately 10 km away from the sampling location of IAP.…”

“…The collection efficiencies (CEs) applied for the ACSM at IAP and BUCT were different. For IAP, a capture vaporizer was used, and the CE was assumed to be close to 1 (Sun et al, 2020). For BUCT, a standard vaporizer was applied with a compositionand acidity-dependent CE calculated according to Middlebrook et al (2012).…”