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A filter-based single-wavelength photometer (Particle Soot Absorption Photometer, PSAP) for measuring light absorption by aerosols was modified to measure at three wavelengths, 467 nm, 530 nm, and 660 nm. The modified and an unmodified photometer were calibrated during the Reno Aerosol Optics Study (RAOS) 2002 against two absorption standards: a photoacoustic instrument and the difference between the extinction and scattering coefficient. This filter-based absorption method has to be corrected for scattering aerosol and transmission changes. A simple function for this was derived from the calibration experiment as a function of transmission and single-scattering albedo. For an unmodified PSAP at typical atmospheric absorption coefficients the algorithm yields about 5-7% lower absorption coefficients than does the usually used method. The three-wavelength PSAP was used for atmospheric measurements both during RAOS and during the New England Air Quality Study (NEAQS).

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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] The reaction of dinitrogen pentoxide with chloridecontaining substrates over a concentration range relevant to the atmosphere was examined using cavity ring-down spectroscopy (CaRDS) and chemical ionization mass spectrometry (CIMS). The main product, nitryl chloride (ClNO 2 ), was formed in efficiencies in the range 0.2 to 0.8 for chloride concentrations of 0.02 to 0.5M. These values are somewhat lower than those from previous, less detailed, measurements carried out mainly at much larger chloride concentrations in NaCl-water mixtures. Substrates having pH<2 also evolved molecular chlorine (Cl 2 ), with ClNO 2 as an intermediate. The ClNO 2 yields are compared to recent field measurements of N 2 O 5 and ClNO 2 as a function of aerosol chloride concentration and shown to quantitatively explain the observations. Citation: Roberts, J.

A ternary nucleation model for the H2SO4-NH3-H20 system is presented in an effort to examine the effect of NH 3 on heteromolecular homogeneous nucleation in the marine boundary layer (MBL). The results from this nucleation model suggest that ammonia could, in fact, enhance the nucleation rate over that of the binary system, H2SO4-H20. The magnitude of this enhancement is introduced as an enhancement ratio, which, in principle, is applicable to any binary nucleation rate for H2SO4-H20. Also presented are preliminary results from a simple aerosol model using this enhancement ratio. These results suggest that under conditions typical of the marine environment it may be possible to produce enough particles to balance the various particle sinks characteristic of the MBL. Introduction It has long been maintained that in situ homogeneousnucleation is an important source of particles in the atmosphere [cf. Kiang et al., 1975]. In describing the aerosol population of the marine boundary layer (MBL), such nucleation has often been parameterized in terms of a binary nucleation process involving H2SO 4 and H20 [Lin et al., 1992; Hegg et al., 1992; Raes and Van Dingenen, 1991]. However, nucleation rates calculated utilizing binary nucleation theory for average MBL conditions have yielded negligible particle production. While atypical conditions have yielded quite significant nucleation, it has been both spatially and temporally variable. It is by no means clear that this production, when averaged over the MBL, is sufficient to offset the various particle sinks. Certainly, such episodic, intense nucleation has been rarely observed. Furthermore, an issue has arisen in that it is similarly unclear that the newly created particles, given the calculated nucleation rates, have a sufficiently long lifetime to grow to such a size that they can become cloud condensation nuclei (CCN). Indeed, a number of recent studies have dealt with possible ways of reconciling calculated nucleation rates with the CCN budget [Lin et al., 1992; Hegg, 1990; Raes and Van Dingenen, 1992; Hoppel et al., 1990]. Considering the possible linkage of the CCN number population to global climate [Charlson et al., 1987], the issue of the proper nucleation theory to use in modeling the MBL aerosol may be of considerable importance.One process which could possibly reconcile particle nucleation rates, growth rates, and particle lifetimes and possibly eliminate the need for intense, episodic nucleation is that of ternary as opposed to binary nucleation. For example, several studies have been conducted in recent years to predict the nucleation rates in the ternary system, H20-H2SO4-methane sulfonic acid [e.g., Kreidenweis and Seinfeld, 1988; Van Dingenen and Raes, 1993]. However, while these assessments have suggested an impact of the third component (i.e., methane sulfonic acid (MSA)) on particle growth, no significant impact on the nucleation rate has been established. Another atmospheric gas with great potential for impact on nucleation rates, especially for the H2...

and the MBL associated with cloud pumping and subsidence following cold frontal passages. There was no evidence of major new particle production in the MBL. Oceanic emissions of DMS appeared to contribute to the growth of Aitken and accumulation mode particles. Coarse mode particles were comprised primarily of sea salt. Although these particles result from turbulence at the air-sea interface, the instantaneous wind speed accounted for only one third of the variance in the coarse mode number concentration in this region.