Abstract
Abstract. A PM2.5-capable aerosol chemical speciation monitor (Q-ACSM) was deployed in urban Nanjing, China, for the first time to measure in situ non-refractory fine particle (NR-PM2.5) composition from 20 October to 19 November 2015, along with parallel measurements of submicron aerosol (PM1) species by a standard Q-ACSM. Our results show that the NR-PM2.5 species (organics, sulfate, nitrate, and ammonium) measured by the PM2.5-Q-ACSM are highly correlated (r2 > 0.9) with those measured by a Sunset Lab OC / EC analyzer and a Monitor for AeRosols and GAses (MARGA). The comparisons between the two Q-ACSMs illustrated similar temporal variations in all NR species between PM1 and PM2.5, yet substantial mass fractions of aerosol species were observed in the size range of 1–2.5 µm. On average, NR-PM1−2.5 contributed 53 % of the total NR-PM2.5, with sulfate and secondary organic aerosols (SOAs) being the two largest contributors (26 and 27 %, respectively). Positive matrix factorization of organic aerosol showed similar temporal variations in both primary and secondary OAs between PM1 and PM2.5, although the mass spectra were slightly different due to more thermal decomposition on the capture vaporizer of the PM2.5-Q-ACSM. We observed an enhancement of SOA under high relative humidity conditions, which is associated with simultaneous increases in aerosol pH, gas-phase species (NO2, SO2, and NH3) concentrations and aerosol water content driven by secondary inorganic aerosols. These results likely indicate an enhanced reactive uptake of SOA precursors upon aqueous particles. Therefore, reducing anthropogenic NOx, SO2, and NH3 emissions might not only reduce secondary inorganic aerosols but also the SOA burden during haze episodes in China.
Highlights
Atmospheric fine particles (PM2.5, aerodynamic diameter ≤ 2.5 μm) are of great concern because they degrade air quality (R. Zhang et al, 2015), reduce visibility (Watson, 2002), and negatively affect human health (Pope and Dockery, 2006)
Organic aerosol (OA) measured by the Aerosol Mass Spectrometer (AMS) can be further deconvolved into various organic classes from different sources and processes using positive matrix factorization (PMF) (Paatero and Tapper, 1994; Lanz et al, 2010; Ulbrich et al, 2009; Zhang et al, 2011), which has greatly improved our understanding of the key atmospheric processes of OA during the last 10 years (Zhang et al, 2007; Jimenez et al, 2009)
The results showed that the PM2.5-Quadrupole Aerosol Chemical Speciation Monitor (Q-ACSM) equipped with the newly developed capture vaporizer (CV) can detect approximately 90 % of the PM2.5 particles, but more thermal decomposition of both inorganic and organic
Summary
Atmospheric fine particles (PM2.5, aerodynamic diameter ≤ 2.5 μm) are of great concern because they degrade air quality (R. Zhang et al, 2015), reduce visibility (Watson, 2002), and negatively affect human health (Pope and Dockery, 2006). Secondary organic aerosols (SOAs) and secondary inorganic aerosols (e.g., sulfate, nitrate, and ammonium) have been found to be of similar importance in leading to the rapid formation and accumulation of PM2.5 during the severe haze events in China (Huang et al, 2014; Sun et al, 2014; Zhang et al, 2014). Limited by the aerodynamic lens, the previous AMS and Q-ACSM only measure aerosol species in PM1 This is reasonable for the studies in the US and Europe where PM1 accounts for a large fraction (typically > 70 %) of PM2.5 (Sun et al, 2011; Budisulistiorini et al, 2014; Petit et al, 2015). Sources of organic aerosols are elucidated by positive matrix factorization (PMF) and new insights into the impacts of aerosol liquid water on the formation of secondary inorganic aerosols and SOA are discussed in this study
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