Primary marine organic aerosol: A dichotomy of low hygroscopicity and high CCN activity

Abstract

[1] High-time resolution measurements of primary marine organic sea-spray physico-chemical properties reveal an apparent dichotomous behavior in terms of water uptake: specifically sea-spray aerosol enriched in organic matter possesses a low hydroscopic Growth Factor (GF∼1.25) while simultaneously having a cloud condensation nucleus/ condensation nuclei (CCN/CN) activation efficiency of between 83% at 0.25% supersaturation and 100% at 0.75%. In contrast, the activation efficiency of particles dominated by non-sea-salt (nss)-sulfate ranged between 48-100% over supersaturation range of 0.25%-1%. Simultaneous retrieval of Cloud Droplet Number Concentration (CDNC) during primary organic aerosol plumes reveals CDNC concentrations of 350 cm −3 for organic mass concentrations 3-4 mg m −3 . It is demonstrated that the retrieved high CDNCs under clean marine conditions can only be explained by organic seaspray and corroborates the high CCN activation efficiency associated with primary organics. It is postulated that marine hydrogels are responsible for this dichotomous behavior.

What do we learn from long-term cloud condensation nuclei number concentration, particle number size distribution, and chemical composition measurements at regionally representative observatories?

“…This is reflected by the D crit distributions at MHD and BRW. The distributions are bimodal, suggesting that the first mode is associated with sea salt and other CCN active marine aerosols in the case of MHD (Ovadnevaite et al, 2011) and the generally highly hygroscopic Arctic background aerosol in BRW .…”

“…The second, less hygroscopic mode can be associated with a variety of other aerosol sources such as particles transported from inland sources that include peat combustion, traffic and industrial emission sources (Ovadnevaite et al, 2011;Taylor et 30 al., 2016) for MHD, or industrial or biomass burning pollution plumes in the Arctic . In the Mediterranean environment the distribution is not bimodal, although it exhibits a small plateau for slightly more hygroscopic particles, while the majority of particles are on average less hygroscopic than in the other coastal areas.…”

Evolving research directions in Surface Ocean - Lower Atmosphere (SOLAS) science

“…[63] Nevertheless, large uncertainties in the number Credit: Surface Ocean-Lower Atmosphere Study Law SOLAS research directions production flux remain, [63] although recent results converge within a factor of 2-3. [75] Advances have also been made in our understanding of the effect of ocean-derived aerosols on climate, particularly with respect to the effects of OM on CCN production, [76][77][78] and on boundary layer chemistry. [79][80][81] There has also been recent recognition that particles of ,1 mm may be a significant source of CCN in marine regions, [70] that is potentially more important than the contribution from the oxidation of DMS.…”

CCN Properties of Organic Aerosol Collected Below and within Marine Stratocumulus Clouds near Monterey, California

“…The presence of POMA is mostly attributed to biological activity, and its concentration varies with season [9,11,12]. POMA can exhibit low hygroscopic growth factors but maintain high CCN activity [13] or vice versa [14]. Secondary organic marine aerosol (SOMA) can be produced during cloud processing [15][16][17][18][19]; perhaps the most studied chemical pathway for SOMA is glyoxylic acid oxidation [20] via several aqueous phase intermediates [21][22][23].…”

“…Continental biogenic emissions can also contribute to organic mass in marine clouds at high altitudes [24]. Anthropogenic emissions can substantially contribute to marine organics; for example, particulate emissions from ships are composed roughly of up to 10% carbon [25,26], in the form of sparingly soluble poly-aromatic hydrocarbons, ketones and quinones (PAHs, PAKs, and PAQs, respectively [13,27]). "Ship tracks" are a natural laboratory for studying aerosol indirect effects, as clouds with uniform dynamics, are exposed to a strong gradient in emissions concentrations and often exhibit droplet number, effective radius and drizzle rates responses that are consistent with local emission rates [28][29][30][31][32].…”