Abstract
Abstract. The chemical composition of aerosol particles (Dp ≤ 1.5 μm) was measured over the southeast Pacific Ocean during the VAMOS (Variability of the American Monsoon Systems) Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-Rex) between 16 October and 15 November 2008 using the US Department of Energy (DOE) G-1 aircraft. The objective of these flights was to gain an understanding of the sources and evolution of these aerosols, and of how they interact 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 (total organics), NH4+, and NO3−, in decreasing order of importance; CH3SO3− (MSA), Ca2+, and K+ rarely exceeded their limits of detection. Aerosols were strongly acidic with a NH4+ to SO42− equivalents ratio typically < 0.3. Sea-salt aerosol (SSA) particles, represented by NaCl, exhibited Cl− deficits caused by both HNO3 and H2SO4, but for the most part were externally mixed with particles, mainly SO42−. SSA contributed only a small fraction of the total accumulation mode particle number concentration. It was inferred that all aerosol species (except SSA) were of predominantly continental origin because of their strong land-to-sea concentration gradient. Comparison of relative changes in median values suggests that (1) an oceanic source of NH3 is present between 72° W and 76° W, (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) free tropospheric (FT) contributions to MBL gas and aerosol concentrations were negligible. The very low levels of CH3SO3− observed as well as the correlation between SO42− and NO3− (which is thought primarily anthropogenic) suggest a limited contribution of DMS to SO42− aerosol production during VOCALS.
Highlights
The southeast Pacific (SEP) region off the coast of Chile and Peru is home to the largest marine stratocumulus cloud deck on the globe
To examine the relationship between all of the species on a common basis, the Aerosol Mass Spectrometer (AMS) data are normalized to the PILS data using the slope of the least-squares fit of the correlation plot of non-sea-salt SO24− concentrations determined by these two methods, one for each flight (Table 2), assuming that nss-SO24− was present only in particles of Dp < 440 nm
The chemical composition of accumulation mode aerosol particles in coastal marine atmospheres off northern Chile was determined on board the Department of Energy (DOE) G-1 using an AMS and the Particle-into-Liquid Sampler – Ion Chromatography (PILS-IC) during 2008 VOCALS-REx
Summary
The southeast Pacific (SEP) region off the coast of Chile and Peru is home to the largest marine stratocumulus cloud deck on the globe. Such decks are typically found on the eastern edges of oceans, and play an important role in the climate system The VAMOS1 Ocean-Cloud-Atmosphere-Land Study-Regional Experiment (VOCALS-Rex) campaign, referred to as VOCALS in this work, was designed to collect observational data to help understand the structure of marine stratocumulus clouds, their radiative properties, and sources of marine aerosol particles that maintain and interact with clouds in the SEP (Wood et al, 2011). Lee et al.: Chemical composition and sources of coastal marine aerosol particles
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