Aqueous-phase secondary organic aerosol and organosulfate formation in atmospheric aerosols: a modeling study.
We have examined aqueous-phase secondary organic aerosol (SOA) and organosulfate (OS) formation in atmospheric aerosols using a photochemical box model with coupled gas-phase chemistry and detailed aqueous aerosol chemistry. SOA formation in deliquesced ammonium sulfate aerosol is highest under low-NO(x) conditions, with acidic aerosol (pH = 1) and low ambient relative humidity (40%). Under these conditions, with an initial sulfate loading of 4.0 μg m(-3), 0.9 μg m(-3) SOA is predicted after 12 h. Low-NO(x) aqueous-aerosol SOA (aaSOA) and OS formation is dominated by isoprene-derived epoxydiol (IEPOX) pathways; 69% or more of aaSOA is composed of IEPOX, 2-methyltetrol, and 2-methyltetrol sulfate ester. 2-Methyltetrol sulfate ester comprises >99% of OS mass (66 ng m(-3) at 40% RH and pH 1). In urban (high-NO(x)) environments, aaSOA is primarily formed via reversible glyoxal uptake, with 0.12 μg m(-3) formed after 12 h at 80% RH, with 20 μg m(-3) initial sulfate. OS formation under all conditions studied is maximum at low pH and lower relative humidities (<60% RH), i.e., when the aerosol is more concentrated. Therefore, OS species are expected to be good tracer compounds for aqueous aerosol-phase chemistry (vs cloudwater processing).
Department of Chemical Engineering, Columbia University, New York, New York 10027, USA. vfm2103@columbia.edu
V Faye
VF
McNeill
Joseph L
JL
Woo
Derek D
DD
Kim
Allison N
AN
Schwier
Neal J
NJ
Wannell
Andrew J
AJ
Sumner
Joseph M
JM
Barakat
D000336:Aerosols; D001272:Atmosphere; D008962:Models, Theoretical; D009930:Organic Chemicals / Q000737:chemistry*; D013455:Sulfur / Q000737:chemistry*
D000336:Aerosols; D009930:Organic Chemicals; D013455:Sulfur