Air-Sea Exchange of Biogenic Volatile Organic Compounds and the Impact on Aerosol Particle Size Distributions

We report simultaneous, underway eddy covariance measurements of the vertical flux of isoprene, total monoterpenes, and dimethyl sulfide (DMS) over the Northern Atlantic Ocean during fall. Mean isoprene and monoterpene sea-to-air vertical fluxes were significantly lower than mean DMS fluxes. While rare, intense monoterpene sea-to-air fluxes were observed, coincident with elevated monoterpene mixing ratios. A statistically significant correlation between isoprene vertical flux and short wave radiation was not observed, suggesting that photochemical processes in the surface microlayer did not enhance isoprene emissions in this study region. Calculations of secondary organic aerosol production rates (PSOA) for mean isoprene and monoterpene emission rates sampled here indicate that PSOA is on average <0.1 μg m−3 d−1. Despite modest PSOA, low particle number concentrations permit a sizable role for condensational growth of monoterpene oxidation products in altering particle size distributions and the concentration of cloud condensation nuclei during episodic monoterpene emission events from the ocean

Wave‐Related Reynolds Number Parameterizations of CO₂ and DMS Transfer Velocities

Predicting future climate hinges on our understanding of and ability to quantify air‐sea gas transfer. The latter relies on parameterizations of the gas transfer velocity k, which represents physical mass transfer mechanisms and is usually parameterized as a nonlinear function of wind forcing. In an attempt to reduce uncertainties in k, this study explores empirical parameterizations that incorporate both wind speed and sea state dependence via wave‐wind and breaking Reynolds numbers, RH and RB. Analysis of concurrent eddy covariance gas transfer and measured wavefield statistics supplemented by wave model hindcasts shows for the first time that wave‐related Reynolds numbers collapse four open ocean data sets that have a wind speed dependence of CO₂ transfer velocity ranging from lower than quadratic to cubic. Wave‐related Reynolds number and wind speed show comparable performance for parametrizing dimethyl sulfide (DMS) which, because of its higher solubility, is less affected by bubble‐mediated exchange associated with wave breaking

Wind Speed and Sea State Dependencies of Air-Sea Gas Transfer: Results From the High Wind Speed Gas Exchange Study (HiWinGS)

A variety of physical mechanisms are jointly responsible for facilitating air-sea gas transfer through turbulent processes at the atmosphere-ocean interface. The nature and relative importance of these mechanisms evolves with increasing wind speed. Theoretical and modeling approaches are advancing, but the limited quantity of observational data at high wind speeds hinders the assessment of these efforts. The HiWinGS project successfully measured gas transfer coefficients (k660) with coincident wave statistics under conditions with hourly mean wind speeds up to 24 m s−1 and significant wave heights to 8 m. Measurements of k660 for carbon dioxide (CO2) and dimethylsulfide (DMS) show an increasing trend with respect to 10-meter neutral wind speed (U10N), following a power-law relationship of the form: math formula and math formula. Among seven high wind speed events, CO2 transfer responded to the intensity of wave breaking, which depended on both wind speed and sea state in a complex manner, with k660 co2 increasing as the wind sea approaches full development. A similar response is not observed for DMS. These results confirm the importance of breaking waves and bubble injection mechanisms in facilitating CO2 transfer. A modified version of the Coupled Ocean-Atmosphere Response Experiment Gas transfer algorithm (COAREG ver. 3.5), incorporating a sea state-dependent calculation of bubble-mediated transfer, successfully reproduces the mean trend in observed k660 with wind speed for both gases. Significant suppression of gas transfer by large waves was not observed during HiWinGS, in contrast to results from two prior field programs

Volcanically influenced iron and aluminum cloud water deposition to Hawaii

Fog or cloud water (CW) deposition plays an important role in particle scavenging and the delivery of trace constituents to the Earth's surface. In this study, CW concentrations of total dissolvable iron (Fe) and aluminum (Al) were measured in 60 samples spanning 26 individual CW events throughout 1999 in Hawaii Volcanoes National Park on the island of Hawaii. Al concentrations ranged from 8 to 10,489 nM, with a median of 344 nM while Fe concentrations ranged from < 1 to 6419 nM with a median of 32 nM. CW deposition fluxes for Fe and Al ranged from 0.15-0.52 mmol Fe m(-2) yr(-1) and 0.62-1.35 mmol Al m(-2) yr(-1), depending on the estimation method used. The large range in concentrations is higher than expected for a relatively pristine ecosystem. It appears that this inconsistency is due to emissions from the currently active nearby volcano, Kilauea. Categorizing CW events into volcanically versus less or non-volcanically impacted events suggests that although volcanically impacted events only accounted for 12% of fog water deposition, Kilauea Volcano was responsible at least 42% of the measured CW Al deposition and 61% of the CW Fe deposition measured for 1999. (C) 2002 Elsevier Science Ltd. All rights reserved

Chemical composition of atmospheric aerosols from Zhenbeitai, China, and Gosan, South Korea, during ACE-Asia

Studies were conducted as part of Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia) to characterize the major ion and elemental composition of aerosol particle samples collected at Gosan, an ACE-Asia supersite (GOS, Korea, total suspended particle or TSP samples) and at Zhenbeitai (ZBT, China, TSP and particles <2.5 mu m diameter or PM2.5 samples), a site closer to the sources for Asia dust. The concentrations of 24 elements in the ZBT PM2.5 samples were correlated with Al (an indicator of mineral dust), and the ratios of these elements to Al were similar to those in a loess certified reference material, but a second group of elements was enriched over crustal proportions most likely as a result of pollution emissions. The concentrations of various water-soluble (WS) cations (Na+, K+, Ca2+, Mg2+) also were generally well correlated with Al in both the ZBT and GOS samples, with the exception being WS K+ at ZBT, where biomass burning may have had an effect. The percentage of calcium that was soluble approached 100% at ZBT versus similar to 60% at GOS, and the ratio WS Ca2+/Al also was higher at ZBT. The molar ratio of sulfate to WS Ca2+ was similar to 0.1 at ZBT but increased to near unity at GOS, where the aerosol nitrate/WS Ca2+ ratio was tenfold to hundredfold higher compared with ZBT, presumably because of anthropogenic influences. The observed differences in aerosol characteristics between sites can only be explained as the end product of different source contributions combined with complex processes involving gas-particle conversion, size-dependent fractionation, and aerosol mixing

Sampling methods used for the collection of particle-phase organic and elemental carbon during ACE-Asia

The semi-volatile nature of carbonaceous aerosols complicates their collection, and for this reason special air sampling configurations must be utilized. ACE-Asia provided a unique opportunity to compare different sampling techniques for collecting carbonaceous aerosols. In this paper detailed comparisons between filter-based carbonaceous aerosol sampling methods are made. The majority of organic carbon (OC) present on a backup quartz fiber filter (QFF) in an undenuded-filter sampler resulted from the adsorption of native gaseous OC rather than OC evaporated from collected particles. The level of OC on a backup QFF placed behind a QFF was lower than the level present on a backup QFF placed behind a Teflon membrane filter (TMF) indicating that gas/filter equilibrium may not be achieved in some QFF front and backup filter pairs. Gas adsorption artifacts can result in a 20-100\% overestimation of the ambient particle-phase OC concentration. The gas collection efficiency of XAD-coated and carbon-impregnated filter-lined denuders were not always 100\%, but, nonetheless, such denuders minimize gas adsorption artifacts. The median fraction of particle-phase OC that is estimated to evaporate from particles collected by denuder-filter samplers ranged from 0 to 0.2; this value depends on the sampler configuration, chemical composition of the OC, and sampling conditions. After properly correcting for sampling artifacts, the measured OC concentration may differ by 10\% between undenuded- and denuder-filter samplers. Uncorrected, such differences can be as large as a factor two, illustrating the importance of sampling configurations in which gas adsorption or evaporation artifacts are reduced or can be corrected. (C) 2003 Elsevier Science Ltd. All rights reserved

Critical assessment of the current state of scientific knowledge, terminology, and research needs concerning the role of organic aerosols in the atmosphere, climate, and global change

In spite of impressive advances in recent years, our present understanding of organic aerosol (OA) composition, physical and chemical properties, sources and transformation characteristics is still rather limited, and their environmental effects remain highly uncertain. This paper discusses and prioritizes issues related to organic aerosols and their effects on atmospheric processes and climate, providing a basis for future activities in the field. Four main topical areas are addressed: i) sources of OA; ii) formation transformation and removal of OA; iii) physical, chemical and mixing state of OA; iv) atmospheric modelling of OA. Key questions and research priorities regarding these four areas are synthesized in this paper, and outstanding issues for future research are presented for each topical area. In addition, an effort is made to formulate a basic set of consistent and universally applicable terms and definitions for coherent description of atmospheric OA across different scales and disciplines