Atmos. Chem. Phys. Discuss., 13, 26043-26115, 2013
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Chemical composition and sources of coastal marine aerosol particles during the 2008 VOCALS-REx campaign
Y.-N. Lee1, S. Springston1, J. Jayne2, J. Wang1, J. Hubbe3, G. Senum1, L. Kleinman1, and P. H. Daum1
1Atmospheric Sciences Division, Brookhaven National Laboratory, Upton, NY 11973, USA
2Aerodyne Research Inc., Bellerica, MA 01821, USA
3Pacific Northwest National Laboratory, P. O. Box 999, K8-88, Richland, WA 99352, USA

Abstract. The chemical composition of aerosol particles (Dp ≤ 1.5 μm) was measured over the southeast Pacific ocean during the VOCALS-REx experiment between 16~October and 15 November 2008 using the US DOE G-1 aircraft. The objective of these flights was to gain an understanding of the sources and evolution of these aerosols, and how they interacted with the marine stratus cloud layer that prevails in this region of the globe. Our measurements showed that the marine boundary layer (MBL) aerosol mass was dominated by non-sea-salt SO42−, followed by Na+, Cl, Org, NH4+, and NO3, in decreasing order of importance; CH3SO3−1 (MSA), Ca2+, and K+ rarely exceeded their limits of detection of ~0.05 and ~0.15 μg m−3 for anions and cations, respectively. The aerosols were strongly acidic as the NH4+ to SO42− equivalence ratio was typically < 0.3; this inferred acidity is corroborated by the conductivity of aqueous samples collected by the PILS. Sea-salt aerosol (SSA) particles, represented by NaCl, showed Cl deficits caused by both HNO3 and H2SO4, and were externally mixed with SO42− particles as the AMS detected no NO3 whilst uptake of HNO3 occurred only on SSA particles. The SSA loading as a function of wind speed agreed with that calculated from published relationships, and contributed only a small fraction of the total accumulation mode particle number. Vertical distribution of MBL SSA particles (Dp ≤ ~1.5 μm) was uniform, suggesting a very limited dilution from entrainment of free tropospheric (FT) air. It was inferred that because all of the aerosol species (except SSA) exhibited a strong land-to-sea gradient, they were of continental origin. Comparison of relative changes in median values using LOWESS fits as proxies suggests that (1) an oceanic source of NH3 is present between 72° W and 76° W, and (2) additional organic aerosols from biomass burns or biogenic precursors were emitted from coastal regions south of 31° S, with possible cloud processing, and (3) FT contributions to MBL gas and aerosols were negligible. Positive Matrix Factorization analysis of organic aerosol mass spectra obtained with the AMS showed an HOA on 28 October 2008 but not on 6 November 2008 that we attribute to a more extensive cloud processing on the later date. A highly oxidized OOA factor resembling fulvic acid was found associated with anthropogenic and biogenic sources as well as long range transported biomass burn plumes in the FT air. A sulfur-containing OOA factor identified as MSA was strongly correlated with SO42−, hence anthropogenic. The very low levels of CH3SO3 observed suggest a limited contribution of DMS to SO42− aerosols production during VOCALS.

Citation: Lee, Y.-N., Springston, S., Jayne, J., Wang, J., Hubbe, J., Senum, G., Kleinman, L., and Daum, P. H.: Chemical composition and sources of coastal marine aerosol particles during the 2008 VOCALS-REx campaign, Atmos. Chem. Phys. Discuss., 13, 26043-26115, doi:10.5194/acpd-13-26043-2013, 2013.
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