[1] An extensive set of volatile organic compounds (VOCs) and particulate organic matter (POM) was measured in polluted air during the New England Air Quality Study in 2002. Using VOC ratios, the photochemical age of the sampled air masses was estimated. This approach was validated (1) by comparing the observed rates at which VOCs were removed from the atmosphere with the rates expected from OH oxidation, (2) by comparing the VOC emission ratios inferred from the data with the average composition of urban air, and (3) by the ability to describe the increase of an alkyl nitrate with time in terms of the chemical kinetics. A large part of the variability observed for oxygenated VOCs (OVOCs) and POM could be explained by a description that includes the removal of the primary anthropogenic emissions, the formation and removal of secondary anthropogenic species, and a biogenic contribution parameterized by the emissions of isoprene. The OVOC sources determined from the data are compared with the available literature, and a satisfactory agreement is obtained. The observed sub-mm POM was highly correlated with secondary anthropogenic gas-phase species, strongly suggesting that the POM was from secondary anthropogenic sources. The results are used to describe the speciation and total mass of gas-and particle-phase organic carbon as a function of the photochemical age of an urban air mass. Shortly after emission the organic carbon mass is dominated by primary VOCs, while after two days the dominant contribution is from OVOCs and sub-mm POM. The total measured organic carbon mass decreased by about 40% over the course of two days. The increase in sub-mm POM could not be explained by the removal of aromatic precursors alone, suggesting that other species must have contributed and/or that the mechanism for POM formation is more efficient than previously assumed.Citation: de Gouw, J. A., et al. (2005), Budget of organic carbon in a polluted atmosphere: Results from the New England Air

We combine in situ measurements of sea salt aerosols (SS) from open ocean cruises and ground-based stations together with aerosol optical depth (AOD) observations from MODIS and AERONET, and the GEOS-Chem global chemical transport model to provide new constraints on SS emissions over the world's oceans. We find that the GEOS-Chem model using the Gong (2003) source function overestimates cruise observations of coarse mode SS mass concentrations by factors of 2–3 at high wind speeds over the cold waters of the Southern, North Pacific and North Atlantic Oceans. Furthermore, the model systematically underestimates SS over the warm tropical waters of the Central Pacific, Atlantic, and Indian Oceans. This pattern is confirmed by SS measurements from a global network of 15 island and coastal stations. The model discrepancy at high wind speeds (>6 m s^−1) has a clear dependence on sea surface temperature (SST). We use the cruise observations to derive an empirical SS source function depending on both wind speed and SST. Implementing this new source function in GEOS-Chem results in improved agreement with in situ observations, with a decrease in the model bias from +64% to +33% for the cruises and from +32% to −5% for the ground-based sites. We also show that the wind speed-SST source function significantly improves agreement with MODIS and AERONET AOD, and provides an explanation for the high AOD observed over the tropical oceans. With the wind speed-SST formulation, global SS emissions show a small decrease from 5200 Mg yr⁻¹ to 4600 Mg yr⁻¹, while the SS burden decreases from 9.1 to 8.5 mg m⁻². The spatial distribution of SS, however, is greatly affected, with the SS burden increasing by 50% in the tropics and decreasing by 40% at mid- and high-latitudes. Our results imply a stronger than expected halogen source from SS in the tropical marine boundary layer. They also imply stronger radiative forcing of SS in the tropics and a larger response of SS emissions to climate change than previously thought

Atmospheric black carbon (BC) warms Earth's climate, and its reduction has been targeted for near-term climate change mitigation. Models that include forcing by BC assume internal mixing with non-BC aerosol components that enhance BC absorption, often by a factor of ~2; such model estimates have yet to be clearly validated through atmospheric observations. Here, direct in situ measurements of BC absorption enhancements (E(abs)) and mixing state are reported for two California regions. The observed E(abs) is small-6% on average at 532 nm-and increases weakly with photochemical aging. The E(abs) is less than predicted from observationally constrained theoretical calculations, suggesting that many climate models may overestimate warming by BC. These ambient observations stand in contrast to laboratory measurements that show substantial E(abs) for BC are possible.

Abstract. A database of 15,617 point measurements of dimethylsulfide (DMS) in surface waters along with lesser amounts of data for aqueous and particulate dirhethylsulfoniopropionate concentration, chlorophyll concentration, sea surface salinity and temperature, and wind speed has been assembled. The database was processed to create a series of climatological annual and monthly 1øxl ø latitude-longitude squares of data. The results were compared to published fields of geophysical and biological parameters. No significant correlation was found between DMS and these parameters, and no simple algorithm could be found to create monthly fields of sea surface DMS concentration based on these parameters. Instead, an annual map of sea surface DMS was produced using an algorithm similar to that employed by Conkright et al. [1994]. In this approach, a first-guess field of DMS sea surface concentration measurements is created and then a correction to this field is generated based on actual measurements. Monthly sea surface grids of DMS were obtained using a similar scheme, but the sparsity of DMS measurements made the method difficult to implement. A scheme was used which projected actual data into months of the year where no data were otherwise present.

[1] The International Global Atmospheric Chemistry Program (IGAC) has conducted a series of Aerosol Characterization Experiments (ACE) that integrate in situ measurements, satellite observations, and models to reduce the uncertainty in calculations of the climate forcing due to aerosol particles. ACE-Asia, the fourth in this series of experiments, consisted of two focused components: (1) An intensive field study that sought to quantify the spatial and vertical distribution of aerosol concentrations and properties, the processes controlling their formation, evolution, and fate, and the column-integrated radiative effect of the aerosol (late March through May 2001). (2) A longer-term network of ground stations that used in situ and column-integrated measurements to quantify the chemical, physical, and optical properties of aerosols in the ACE-Asia study area and to assess their spatial and temporal (seasonal and interannual) variability (2000)(2001)(2002)(2003). The approach of the ACE-Asia science team was to make simultaneous measurements of aerosol chemical, physical, and optical properties and their radiative impacts in a variety of air masses, often coordinated with satellite overpasses. Three aircraft, two research ships, a network of lidars, and many surface sites gathered data on Asian aerosols. Chemical transport models (CTMs) were integrated into the program from the start, being used in a forecast mode during the intensive observation period to identify promising areas for airborne and ship observations and then later as tools for integrating observations. The testing and improvement of a wide range of aerosol models (including microphysical, radiative transfer, CTM, and global climate models) was one important way in which we assessed our understanding of the properties and controlling processes of Asian aerosols. We describe here the scientific goals and objectives of the ACE-Asia experiment, its observational strategies, the types of observations made by the mobile platforms and stationary sites, the models that will integrate our understanding of the climatic effect of aerosol particles, and the types of data that have been generated. Eight scientific questions focus the discussion. The intensive observations took place during a season of unusually heavy dust, so we have a large suite of observations of dust and its interaction with air pollutants. Further information about ACE-Asia can be found on the project Web site at http://saga.pmel.noaa.gov/aceasia/.

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Emissions of sulfur gases from both natural and anthropogenic sources strongly influence the chemistry of the atmosphere. To assess the relative importance of these sources we have combined the measurements of sulfur gases and fluxes during the past decade to create a global emission inventory. The inventory, which is divided into 12 latitude belts, takes into account the seasonal dependence of sulfur emissions from biogenic sources. The total emissions of sulfur gases from natural sources are approximately 0.79 Tmol S/a. These emissions are 16% of the total sulfur emissions in the Northern Hemisphere and 58% in the Southern Hemisphere. The inventory clearly shows the impact of anthropogenic sulfur emissions in the region between 35 ° and 50°N.