Open AccessTime‐ and size‐resolved chemical composition of submicron particles in Pittsburgh: Implications for aerosol sources and processes
Author(s) -
Zhang Qi,
Canagaratna Manjula R.,
Jayne John T.,
Worsnop Douglas R.,
Jimenez JoseLuis
Publication year - 2005
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2004jd004649
Subject(s) - sulfate , aerosol , ammonium sulfate , nitrate , environmental chemistry , ammonium , particulates , environmental science , ammonium nitrate , chemical composition , particle size , mass concentration (chemistry) , particle (ecology) , air quality index , total organic carbon , chemistry , atmospheric sciences , mineralogy , meteorology , geology , chromatography , physics , oceanography , organic chemistry
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).