[1] In situ measurements of the mass, mixing state, and optical size of individual black-carbon (BC) particles in the fine mode (90 -600 nm) have been made in fresh emissions from urban and biomass burning sources with an airborne single-particle soot photometer. Contrasts between the two sources are significant and consistent. Urban BC tends to smaller sizes, fewer coated particles, thinner coatings, and less absorption per unit mass than biomass-burning BC. This suggests that urban BC may have a longer lifetime in the atmosphere and a different impact on BC radiative forcing in the first indirect effect than biomass-burning BC. These measurements bound the likely variability in the microphysical state of BC emissions from typical continental processes, and provide direct measurements of the size distribution and coating state of fine-mode BC for use in constraining climate and aerosol models. These results highlight the need for the integration of sourcespecific information into such models. Citation: Schwarz, J. P., et al. (2008), Measurement of the mixing state, mass, and optical size of individual black carbon particles in urban and biomass burning emissions, Geophys. Res. Lett., 35, L13810,

Light absorption by aerosols is one of the most uncertain parameters associated with the direct and indirect aerosol effects on climate and is one of the most difficult quantities to measure. This article describes the development of a sensitive method of measuring aerosol absorption at 532 nm with excellent time response (detection limit: 0.08 Mm −1 , 60 second average) using photoacoustic absorption spectroscopy. An accurate calibration method (accuracy of 1-2%) at atmospherically relevant absorption levels and independent validation of the photoacoustic technique is presented. An upper limit to the instrument precision for aerosol absorption measurement is ∼6% (2σ , 30 sec) while instrument accuracy is calculated to be ∼5%. A standard for aerosol absorption measurement techniques using well characterized absorbing aerosol is also proposed.

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, 39% OM, and 15% BC and differs from inventories that used 81%, 14%, and 5% and 31%, 63%, and 6% SO 4 2À , OM, and BC, respectively. SO 4 2À and OM mass were found to be dependent on fuel sulfur content as were SSA, hygroscopicity, and CCN concentrations. BC mass was dependent on engine type and combustion efficiency. A plume evolution study conducted on one vessel showed conservation of particle light absorption, decrease in CN > 5 nm, increase in particle hygroscopicity, and an increase in average particle size with distance from emission. These results suggest emission of small nucleation mode particles that subsequently coagulate/condense onto larger BC and OM. This work contributes to an improved understanding of the impacts of ship emissions on climate and air quality and will also assist in determining potential effects of altering fuel standards.

[1] Measurements were made on board the NOAA RV Ronald H. Brown during the second New England Air Quality Study (NEAQS 2004) to determine the source of the aerosol in the region and how sources and aging processes affect submicrometer aerosol chemical composition and optical properties. Using the Lagrangian particle dispersion model FLEXPART in combination with gas phase tracer compounds, local (urban), regional (NE U.S. urban corridor of Washington, D.C.; New York; and Boston), and distant (midwest industries and North American forest fires) sources were identified. Submicrometer aerosol measured near the source region (Boston Harbor) had a molar equivalence ratio near one with respect to NH 4 + , NO 3 À , and SO 4 = , had a large mass fraction of particulate organic matter (POM) relative to SO 4 = , and had relatively unoxidized POM. As distance from the source region increased, the submicrometer aerosol measured in the marine boundary layer became more acidic and had a lower POM mass fraction, and the POM became more oxidized. The relative humidity dependence of light extinction reflected the change in aerosol composition being lower for the near-source aerosol and higher for the more processed aerosol. A factor analysis performed on a combined data set of aerosol and gas phase parameters showed that the POM measured during the experiment was predominantly of secondary anthropogenic origin.Citation: Quinn, P. K., et al. (2006), Impacts of sources and aging on submicrometer aerosol properties in the marine boundary layer across the Gulf of Maine,

Measurements during recent field campaigns downwind of the Indian subcontinent, Asia, and the northeastern United States reveal a substantial decrease in the relative humidity dependence of light scattering, fσsp(RH), with increasing mass fraction of particulate organic matter (POM) for submicrometer aerosol. Using data from INDOEX (INDian Ocean EXperiment), ACE Asia (Aerosol Characterization Experiment – Asia), and ICARTT (International Consortium for Atmospheric Research on Transport and Transformation), we have identified, within measurement limitations, the impact of POM on the fσsp(RH) of accumulation mode sulfate‐POM mixtures. The result is a parameterization that quantifies the POM mass fraction ‐ fσsp(RH) relationship for use in radiative transfer and air quality models either as input or as validation. The parameterization is valid where the aerosol consists of an internally mixed sulfate‐carbonaceous accumulation mode and other externally mixed components (e.g. sea salt, dust) and is applicable on both global and regional scales.

[1] Atmospheric particles are a complex mixture of inorganic and organic compounds. This study uses laboratory generated particles to examine the connection between aerosol light extinction, chemical composition, and hygroscopicity for particles composed of internal mixtures of ammonium sulfate and water-soluble organic compounds. The extinction coefficient (s ep ) at 532 nm was measured for size-selected particles at <10% RH and 80% RH. The ratio of the extinction coefficients at 80% RH to <10% RH is reported as fRH ext (80% RH, dry). The fRH ext (80% RH, dry) values were similar for particles composed of various water-soluble organic compounds and different functional groups. In addition, fRH ext (80% RH, dry) values were relatively insensitive to the composition of the organic fraction for internal mixtures of ammonium sulfate with sugars, dicarboxylic acids and complex mixtures of water-soluble organic compounds. Finally, fRH ext (80% RH, dry) was found to vary linearly with the organic/inorganic content, allowing for simple incorporation of organic properties into atmospheric models. We derived a generalization of fRH ext (80% RH, dry) = 2.90 -0.015(wt% organic species) for a particle size distribution with a dry mean optical diameter of 0.35 mm. This parameterization for ammonium sulfate/water-soluble organic aerosol is applicable to the fine particle mode fraction of atmospheric aerosol. Information necessary to incorporate the variation in the size distribution is also included. This work suggests that neglecting the water uptake by the organic fraction of atmospheric particles could lead to significant underestimation of the cooling at the Earth's surface due to light scattering by aerosol.Citation: Garland, R. M., A. R. Ravishankara, E. R. Lovejoy, M. A. Tolbert, and T. Baynard (2007), Parameterization for the relative humidity dependence of light extinction: Organic-ammonium sulfate aerosol,

This paper describes the design and application of a pulsed cavity ring-down aerosol extinction spectrometer (CRD-AES) for insitu atmospheric measurement of the aerosol extinction coefficient and its relative humidity dependence. This CRD-AES measures the aerosol extinction coefficient (σ ep ) at 355 nm, 532 nm, 683 nm, and 1064 nm with a minimal size dependent bias for particles with diameter less than 10 μm. The σ ep at 532 nm is measured with an accuracy of 1% when extinction is ≥10 Mm −1 . The precision is limited by statistical fluctuations within the small optical volume and the time resolution of extinction at 2% uncertainty for various air mass types is evaluated. The CRD-AES is configured with two separate cavity ring-down cells for measurement of the extinction coefficient at 532 nm. This allows the determination of the RH dependence of extinction at 532 nm through independent RH control of the sample for each measurement. Gas phase absorption and minimization of potential interferences is also considered.