Sources and composition of submicron organic mass in marine aerosol particles

Abstract

The sources and composition of atmospheric marine aerosol particles (aMA) have been investigated with a range of physical and chemical measurements from open-ocean research cruises. This study uses the characteristic functional group composition (from Fourier transform infrared spectroscopy) of aMA from five ocean regions to show the following: (i) The organic functional group composition of aMA that can be identified as mainly atmospheric primary marine (ocean derived) aerosol particles (aPMA) is 65 ± 12% hydroxyl, 21 ± 9% alkane, 6 ± 6% amine, and 7 ± 8% carboxylic acid functional groups. Contributions from photochemical reactions add carboxylic acid groups (15%-25%), shipping effluent in seawater and ship emissions add additional alkane groups (up to 70%), and coastal or continental emissions mix in alkane and carboxylic acid groups. (ii) The organic composition of aPMA is nearly identical to model-generated primary marine aerosol particles from bubbled seawater (gPMA, which has 55 ± 14% hydroxyl, 32 ± 14% alkane, and 13 ± 3% amine functional groups), indicating that its overall functional group composition is the direct consequence of the organic constituents of the seawater source. (iii) While the seawater organic functional group composition was nearly invariant across all three ocean regions studied and the ratio of organic carbon to sodium (OC/Na + ) in the gPMA remained nearly constant over a broad range of chlorophyll a concentrations, the gPMA alkane group fraction appeared to increase with chlorophyll a concentrations (r = 0.66). gPMA from productive seawater had a larger fraction of alkane functional groups (42 ± 9%) compared to gPMA from nonproductive seawater (22 ± 10%), perhaps due to the presence of surfactants in productive seawater that stabilize the bubble film and lead to preferential drainage of the more soluble (lower alkane group fraction) organic components. gPMA has a hydroxyl group absorption peak location characteristic of monosaccharides and disaccharides, where the seawater organic mass hydroxyl group peak location is closer to that of polysaccharides. This may result from the larger saccharides preferentially remaining in the seawater during gPMA and aPMA production.

Global distribution and surface activity of macromolecules in offline simulations of marine organic chemistry

“…10 and 11, but their influence is now more tightly confined to productive ring ecosystems of the Southern Ocean (Longhurst 1998). This result is consistent with a correlation of alkyl to ocean chlorophyll, as observed in the spectroscopic analyses of Frossard et al (2014).…”

“…In addition to the fresh and conceptually pure polysaccharides of Table 1, both peptidoglycan and the heteropolycondensates are carbohydrate-rich, so that they could play into any alternate mechanisms Spectroscopic analysis can also be extended beyond alkyl versus hydroxyl to include a wide range of organic functional groups. Amines and amides have been reported in some regions, and these would in fact be consistent with the high protein excess obtained here in our Langmuir scenario (Russell et al 2010;Frossard et al 2014). The actual molar ratios of major functional groups in seawater organics are presented in Table 4 as derived from standard analog compound structures.…”

“…Fourier transform infrared spectroscopy (FTIR) was used to determine amounts of the major bonding structures. A key finding has been that carbon-hydrogen moieties (meaning alkanes) and the hydroxyl (generally in carbohydrate-like structures) are present in roughly equal proportions, whether in clean marine particles or bubbling analogs (Russell et al 2010;Frossard et al 2014). Proteins are the dominant surfactant species in our baseline run, but on average they contain only a low ratio of OH to CH.…”

High summertime aerosol organic functional group concentrations from marine and seabird sources at Ross Island, Antarctica, during AWARE

“…5), but their low concentrations did not support further investigation. The 1680 cm −1 peak has not been observed in open-ocean marine factors Frossard et al, 2014a), suggesting that an open-ocean marine source is not likely. An alternative explanation of the amide group is emissions from seasonal ice microbiota (Dall'Osto et al, 2017).…”

“…6). Carboxylic acid group mass fractions have also been identified as secondary photochemical products based on their correlation to solar radiation in clean, open-ocean conditions (Frossard et al, 2014a). However, since the seabird emissions were only high in summer when radiation was also generally high, the correlation to radiation does not provide evidence of photochemical contributions in this case.…”