Potential origin of organic cloud condensation nuclei observed at marine site

Abstract

Abstract. Observations by Novakov and Penner [ 1993] (hereinafter, NP) suggest that organic aerosol particles may make up a significant portion of cloud condensation nuclei (CCN), comparable perhaps to the sulfate aerosol contribution to CCN. Because organic CCN would influence the albedo and radiative properties of clouds and play a role in climate change, it is important to identify the sources of these aerosols. In their research, Novakov and Penner showed that particles larger than 0.05 gm could act as CCN at supersaturation ratios of 0.5% water vapor. Here we use model simulations to investigate the origins of the nucleation mode aerosol (0.03 < dp < 0.1 gm) observed at a marine site in Puerto Rico by NP. NP measured the size segregated mass and composition of the atmospheric aerosol at this site and found that organic aerosol mass dominated the total mass in the nucleation mode. The presence of organics in this size range may be the result of nucleation of a gas phase organic and/or condensational growth. Therefore identifying sources of the gas phase precursors is important to determining the origins of the organic CCN. Back trajectory analysis (J. Merrill, private communication, 1994) shows that the air mass that Novakov and Penner studied was without continental contact for 8-12 days prior to being sampled. This implicates two possible sources for the gas phase organic: biogenic emissions from the Puerto Rican forest upwind of the mountain sampling site and emissions from the ocean surface. In this study both the forest and ocean source scenarios are explored. Using input parameters taken from the literature, it is shown that an assumed organic vapor flux for the forest scenario, very similar to the measured biogenic fluxes reported by Zimmerman et al. [ 1988], generated size distributions similar to the observed aerosol. In contrast, literature estimates for the n-alkane vapor flux from the ocean are not consistent with the observed size distribution at the mountain site.

Observations of organic material in individual marine particles at Cape Grim during the First Aerosol Characterization Experiment (ACE 1)

“…additional sodium sulfate in sea salt is produced by reactive uptake of sulfuric acid formed by the gas-phase oxidation pathway. Oxidation of gaseous organic species emitted by the oceans produces compounds with lower vapor pressures, some of which would have a tendency to condense on preexisting particles such as sea salt [Eichmann et al, 1980;Grosjean and Seinfeld, 1989;Andrews et al, 1997]. Unlike sulfuric acid, these compounds may not necessarily react with the sea salt or be soluble in aqueous solutions.…”

Spatial distributions of oxygenated organic compounds (dicarboxylic acids, fatty acids, and levoglucosan) in marine aerosols over the western Pacific and off the coast of East Asia: Continental outflow of organic aerosols during the ACE‐Asia campaign

“…Organic compounds as well as sulfates are major components in sub‐micron aerosols, contributing significantly to the scattering of sunlight (direct effect) under various circumstances [ Mazurek et al , 1991; Penner , 1995]. Furthermore, polar organic compounds are hypothesized to make aerosol particle surfaces hydrophilic, which enhances the particle's ability to serve as cloud condensation nuclei (CCN) [ Novakov and Penner , 1993; Rivera‐Carpio et al , 1996; Andrews et al , 1997; Matsumoto et al , 1997; Yu , 2000]. The number of CCN affects cloud radiative properties (indirect effect).…”

Reactive uptake of ozone by proxies for organic aerosols: Surface versus bulk processes

“…Organics may either enhance or diminish water uptake, depending upon whether the organic matter is primary, urban and hydrophobic or secondary, nonurban and more hydrophilic [Saxena et al, 1995]. The water-soluble organic fraction has been shown to have a source in both oceanic environments and forest areas [Andrews et al, 1997;Novakov et al, 1997a]. The nature of the organic component in tropospheric aerosols thus plays an important role in determining their cloud nucleating properties, and hence their effect on climate.…”