National Oceanic and
Atmospheric Administration
United States Department of Commerce


FY 2010

Carboxylic acids, sulfates, and organosulfates in processed continental organic aerosol over the Southeast Pacific Ocean during VOCALS-REx 2008

Hawkins, L.N., L.M. Russell, D.S. Covert, P.K. Quinn, and T.S. Bates

J. Geophys. Res., 115, D13201, doi: 10.1029/2009JD013276 (2010)

Submicron particles were collected on board the NOAA R/V Ronald H. Brown during the VAMOS Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) in the southeast Pacific marine boundary layer in October and November 2008. The aerosol in this region was characterized by low numbers of particles (150–700 cm–3) that were dominated by sulfate ions at concentrations of 0.9 ± 0.7 µg m–3 and organic mass at 0.6 ± 0.4 µg m–3, with no measurable nitrate and low ammonium ion concentrations. Measurements of submicron organic aerosol functional groups and trace elements show that continental outflow of anthropogenic emissions is the dominant source of organic mass (OM) to the southeast Pacific with an additional, smaller contribution of organic mass from primary marine sources. This continental source is supported by a correlation between OM and radon. Saturated aliphatic C-CH (alkane) composed 41 } 27% of OM. Carboxylic acid COOH (32 ± 23% of OM) was observed in single particles internally mixed with ketonic carbonyl, carbonate, and potassium. Organosulfate COSO3 (4 ± 8% of OM) was observed only during the periods of highest organic and sulfate concentrations and lowest ammonium concentrations, consistent with a sulfuric acid epoxide hydrolysis for proposed surrogate compounds (e.g., isoprene oxidation products) or reactive glyoxal uptake mechanisms from laboratory studies. This correlation suggests that in high]sulfate, low]ammonium conditions, the formation of organosulfate compounds in the atmosphere contributes a significant fraction of aerosol OM (up to 13% in continental air masses). Organic hydroxyl C-OH composed 20 ± 12% of OM and up to 50% of remote marine OM and was inversely correlated with radon indicating a marine source. A two]factor solution of positive matrix factorization (PMF) analysis resulted in one factor dominated by organic hydroxyl (>70% by mass) and one factor dominated by saturated aliphatic C-CH (alkane) and carboxylic acid (together, 90% by mass), identified as the marine and combustion factors, respectively. Measurements of particle concentrations in the study region compared with concentrations estimated from MODIS aerosol optical depth indicate that continental outflow results in MBL particle concentrations elevated up to 2 times the background level (less than 300 cm–3) away from shore and up to 10 times the background level at the coast. The presence of both coastal fossil fuel combustion and marine sources of oxygenated organic aerosol results in little change in the oxygenated fraction and oxygen to carbon ratio (O/C) along the outflow of the regionfs dominant organic particle source.

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