Organic matter and non-refractory aerosol over the remote Southeast Pacific: oceanic and combustion sources

Abstract

(SO 4 ) and organics (Org), during VOCALS and the cruise show lower absolute values than those reported for previous "clean air" studies. In the marine boundary layer, average concentrations for SO 4 were 0.52 µg m −3 for the VOCALS region and 0.85 µg m −3 for the equatorial region while average Org concentrations were 0.10 and 0.07 µg m −3 , respectively. Campaign average Org/SO 4 ratios were 0.19 (VOCALS) and 0.08 (equatorial Pacific). Black carbon (BC) measurements from a single particle soot photometer (SP2) and carbon monoxide (CO) concentrations over the Southeast Pacific provided sensitive indicators of pollution. CO and BC were used to identify the least polluted air, which had average concentrations of SO 4 and Org of 0.14 and 0.01 µg m −3 , respectively, with an average Org/SO 4 of 0.08. Data from IMPEX was constrained to similar clean air criterion, and resulted in an average Org/SO 4 ratio of 0.19. Under the cleanest MBL conditions during VOCALS, identified by CO below 61 ppbv, a robust linear relationship between Org and BC concentrations revealed that even at very low pollution levels, combustion sources dominated organic aerosol, suggesting little to no marine source of submicrometer Org to the atmosphere over the eastern South Pacific. This means marine organics cannot be identified by merely setting a standard for background conditions below which anthropogenic influence can be disregarded. Other methods must be used to exclude nonmarine sources.

Impact of marine biogeochemistry on the chemical mixing state and cloud forming ability of nascent sea spray aerosol

“…It is notable that this hygroscopicity parameter value is similar to published values for artificial seawater and other inorganic proxies [Niedermeier et al, 2008;Fuentes et al, 2011], but is higher than many field observations made in the marine boundary layer (κ~0.72; Table 1) [Hudson, 2007;Allan et al, 2008;Furutani et al, 2008;Bougiatioti et al, 2009;Good et al, 2010;Pringle et al, 2010;Martin et al, 2011;Mochida et al, 2011;Moore et al, 2012]. This difference is attributed to the inability of ambient aerosol measurements in the MBL to fully deconvolute influence from secondary marine, continental, and/or anthropogenic sources [Sorooshian et al, 2009;Langley et al, 2010;Shank et al, 2012] in addition to possible contributions from oceanic organic matter in SSA.…”

Impacts of aerosol particles on the microphysical and radiative properties of stratocumulus clouds over the southeast Pacific Ocean

“…The solar zenith angle at 10:30 local time was used for both the satellite and in-situ albedo calculations. Typical levels of absorbing black carbon (< 50 ng m −3 ) measured from the C-130 in VOCALS (Shank et al, 2012) should have a negligible effect on cloud albedo (Twohy et al, 1989b). Figure 14b shows cloud albedos derived from the two techniques (in-situ and remote sensing).…”

Impact of natural and anthropogenic aerosols on stratocumulus and precipitation in the Southeast Pacific: a regional modelling study using WRF-Chem

“…This is because their overall cooling effect is important to the earth's energy budget and also because these boundary layer clouds are often close to emission sources. With a large and persistent stratocumulus cloud deck (Klein and Hartmann, 1993) and a complex mixture of aerosols from anthropogenic and marine sources (Chand et al, 2010;Kleinman et al, 2012;Shank et al, 2012), the Southeast Pacific (SEP) is an ideal location for studying effects of aerosols on shallow warm clouds. Observations from the VAMOS Ocean-Cloud-AtmosphereLand Study Regional Experiment (VOCALS-REx; Wood et al, 2011b) show distinctly different cloud and precipitation features over the remote and near-coast regions over the SEP associated with low and high concentrations of CCN (e.g., Bretherton et al, 2010b;Painemal and Zuidema, 2010;Wood et al, 2011a;Zheng et al, 2011;Zuidema et al, 2012), which resemble the pristine precipitating and the polluted non-precipitating cloud regimes predicted by previous studies (e.g., Baker and Charlson, 1990).…”

“…In the YSU scheme, the non-local mixing due to large eddy transport is considered for heat and momentum components, and an explicit treatment of entrainment is included in the heat and momentum flux profiles and the growth of the planetary boundary layer (PBL) height (Noh et al, 2003;Shin and Hong, 2011). This parameterized PBL entrainment in the YSU scheme is not equivalent to cloud-top entrainment (S. Hong, personal communication, 2012) since the YSU scheme assumes the PBL top as the minimum flux level as explicitly formulated, and the PBL height from YSU was found to be near the cloud base or mid-level of the stratocumulus clouds.…”