Sources of organic aerosols in the southeastern Pacific during 2008 VOCALS-REX

 

Authors

Yin-Nan Lee — Brookhaven National Laboratory
Stephen R. Springston — Brookhaven National Laboratory
Jian Wang — Washington University in St. Louis
Gunnar I. Senum — Brookhaven National Laboratory
John T Jayne — Aerodyne Research, Inc.
John Hubbe — Pacific Northwest National Laboratory
Larry Kleinman — Brookhaven National Laboratory
Peter Daum — Brookhaven National Laboratory

Category

Aerosol Properties

Description

Concentrations of organic aerosol along with that of sulfate and ammonium over the northern Chilean coastal waters of the southeastern Pacific were determined using an Aerodyne cToF-AMS outfitted on the DOE G-1 aircraft during the 2008 VOCALS-REX campaign. Sea-salt aerosol (SSA, as NaCl) and nitrate were determined using the PILS-IC technique. Although all of the aerosol components except SSA exhibited a prominent east-west concentration gradient decreasing with distance from the shore consistent with their terrestrial origins, sulfate as well as nitrate decreased much faster than organics, suggesting additional organic sources toward the open ocean compared to near shore regions. Because the terrestrial emissions impacting the coastal marine boundary layer were transported by a fairly uniform south-southeasterly wind after land contact, the observed concentrations on the G-1 along a narrow latitude band (~19 S) upward of ~78 W are expected to reflect a distributed terrestrial source region that shifted progressively from north to south as offshore distance increases. While an increased organic relative to sulfate source from north to south is consistent with additional biogenic sources south of ~30 S where the Atacama desert to the north ends, other potential contributions such as ocean emissions and entrainment from free troposphere may also be appreciable and should be considered. Despite the low organic aerosol loadings observed on the G-1 during VOCALS (i.e., max < 1 µg m-3, median < 0.3 µg m-3), we attempt to determine their sources using the PMF technique; three factors resembling HOA, OOA, and BBOA are tentatively assigned. The validity and relative importance of these different sources are examined in term of their relationships to (1) sulfate, ammonium, and nitrate, which are anthropogenic from the land, (2) CO, which is advected from the land but can also be entrained into the marine boundary layer from the free troposphere, and (3) SSA, which is produced from ocean surfaces mainly by wind stress. Evidence for the purported marine originated small organic aerosol particles (D < 0.1 µm) generated either by bubble film bursting and/or by oceanic SOA precursors is also investigated.