Time‐ and size‐resolved chemical composition of submicron particles in Pittsburgh: Implications for aerosol sources and processes

Abstract

[1] An Aerodyne aerosol mass spectrometer (AMS) was deployed at the Pittsburgh Environmental Protection Agency Supersite from 7 to 22 September 2002 as part of the Pittsburgh Air Quality Study (PAQS). The main objectives of this deployment were to characterize the concentrations, size distributions, and temporal variations of nonrefractory (NR) chemical species in submicron particles (approximately PM 1 ) and to further develop and evaluate the AMS. Reasonably good agreement was observed on particle concentrations, composition, and size distributions between the AMS data and measurements from collocated instruments (given the difference between the PM 1 and PM 2.5 size cuts), including TEOM, semicontinuous sulfate, 2-hour-and 24-hour-averaged organic carbon, SMPS, 4-hour-averaged ammonium, and micro-orifice uniform deposit impactor. Total NR-PM 1 mass concentration in Pittsburgh accumulates over periods of several days punctuated with rapid cleaning due to rain or air mass changes. Sulfate and organics are the major NR-PM 1 components while the concentrations of nitrate and chloride are generally low. Significant amounts of ammonium, which most of the time are consistent with sulfate present as ammonium sulfate, are also present in particles. However, there are periods when the aerosols are relatively acidic and more than 50% of sulfate is estimated to be in the form of ammonium bisulfate. No major enhancement of the organic concentration is observed during these acidic periods, which suggests that acid-catalyzed SOA formation was not an important process during this study. Size distributions of particulate sulfate, ammonium, organics, and nitrate vary on timescales of hours to days, showing unimodal, bimodal and even trimodal characteristics. The accumulation mode (peaking around 350-600 nm in vacuum aerodynamic diameter for the mass distributions) and the ultrafine mode (<100 nm) are observed most frequently. The accumulation mode is dominated by sulfate that appears to be internally mixed with oxidized organics, while combustion-emitted organics are often the main component of the ultrafine particles (except during nucleation events). The ultrafine-mode organic aerosols are mainly associated with combustion sources (likely traffic).

Influence of Intense secondary aerosol formation and long range transport on aerosol chemistry and properties in the Seoul Metropolitan Area during spring time: Results from KORUS-AQ

“…S3c, the SMPS-measured particle volume correlated strongly with the 17 AMS measured total mass (R 2 = 0.88). The slope from the linear fit of PM1 mass against SMPS 18 volume is 1.24 g/cm 3 , which was lower than the average (± 1) particle density of 1.50 (± 0.08) 19 g/cm 3 estimated using the measured chemical composition in this study (Zhang et al, 2005b) (Fig. 20 S3d).…”

Acid-catalyzed reactions of hexanal on sulfuric acid particles: Identification of reaction products

“…The concentrations of other species are quantified by using ''relative ionization efficiencies'' (RIEs) determined during calibration experiments with those species (Alfarra et al, 2004). Organic species of many different types have very similar RIEs around 1.4 (Takegawa et al, 2005;Zhang et al, 2005). Together with the RIEs and comparing the collected mass spectrum to known fragmentation patterns, the mass from specific species (i.e.…”

“…However, when both SO 2 and VOC concentrations were elevated, particle growth exceeded that which could be explained by SO 2 oxidation alone; suggesting the VOCs are incorporated into the aerosols (Brock et al, 2003). However, other field studies have not found a significant difference between the organic mass concentrations between periods when ambient sulfate aerosols were acidic or neutralized (Zhang et al, 2005). Thus, laboratory studies are needed to evaluate the potential importance of this type of reaction in the atmosphere.…”

Technical Note: Use of a beam width probe in an Aerosol Mass Spectrometer to monitor particle collection efficiency in the field

“…However, in previous studies using the AMS Drewnick et al, 2004b;Hogrefe et al, 2004;Zhang et al, 2005b) it has been observed that there is a systematic (but highly reproducible) underestimation of the mass concentration of aerosols measured with the AMS when compared to other quantitative aerosol measurements such as the Particle Into Liquid Sampler (PILS) or Scanning Mobility Particle Sizer (SMPS). In these studies, the underestimation in mass concentration observed with the AMS indicates AMS Collection Efficiencies (CE) ranging from 0.43 to 1.…”