Two Aerodyne Aerosol Mass Spectrometers (AMS) were deployed at three sites representing urban, semi-rural and rural areas during the Pacific 2001 experiment in the Lower Fraser Valley (LFV), British Columbia, Canada in August 2001. The AMS provides on-line quantitative measurements of the size and chemical composition of the non-refractory fraction of submicron aerosol particles. A significant accumulation mode with a peak around 400-500 nm was observed at all sites that was principally composed of sulphate, organics, ammonium and some nitrate. Another significant mode with a peak below 200 nm was also observed at the urban site and when urban plumes affected the other sites. This paper focuses on the variability of the organic particulate composition and size distribution as a function of location and photochemical activity with a particular emphasis on the urban and rural areas. The small organic mode at the urban site was well correlated with gas phase CO, 1,3-butadiene, benzene and toluene with Pearson's r values of 0.76, 0.71, 0.79 and 0.69, respectively, suggesting that combustion-related emissions are likely to be the main source of the small organic mode at this site. The mass spectra of the urban organic particulate are similar to those of internal combustion engine lubricating oil, and of diesel exhaust aerosol particles, implying that they were composed of a mixture of n-alkanes, branched alkanes, cycloalkanes, and aromatics. In contrast, organic particulate at the rural site was dominated by shorter chain oxidized organic compounds. Correlations between the two organic modes and gas phase compounds at the rural site indicated that a significant part of the small mode originated from combustion sources, while the large accumulation organic mode appeared to be the result of photochemical processing. Processing of organic particulate during a relatively high O 3 episode at the rural site appeared to increase the modal diameter of the accumulation mode from about 400 to 600 nm and almost doubled its mass loading. r

[1] Two Aerodyne aerosol mass spectrometers (AMSs) were deployed at Trinidad Head on the north Californian coast during the National Oceanographic and Atmospheric Administration Intercontinental Transport and Chemical Transformation 2002 (ITCT 2K2) experiment, to study the physiochemical properties of submicron aerosol particles within the Pacific marine boundary layer. One AMS was modified to allow the study of sea saltbased particles, while the other used a temperature cycling system on its inlet. The reported loadings increased by a factor of 2 when the temperature approached the dew point, which is due to the inlet performance and has implications for other AMS experiments and applications. The processed data were compared with those of a particle into liquid sampler-ion chromatograph and showed that the ammonium, sulfate and organic fractions of the particles were consistently found within a single, normally acidic, accumulation mode at around 300-400 nm. However, when influenced by land-based sources, vehicle emissions and increased ammonium loadings were seen. The concentrations of nitrate in the accumulation mode were low, but it was also found within sea salt particles in the coarse mode and can be linked to the displacement of chloride. The organic fraction showed a high degree of chemical ageing and evidence of nitrogenbearing organics was also observed. The particulate organic data were compared to the volatile organic carbon data derived from an in-situ gas chromatograph-mass spectrometer-flame ionization detector and relationships were found between the gas and particle phase chemicals in both the overall concentrations and the levels of oxidation.

No abstract

No abstract

Abstract. C2-Cs hydrocarbons were measured in situ at Alert, Nunavut, Canada from April 14 to May 10, 1998 at a minimum frequency of 12 samples per day. During the sampling period, an event occurred where the O3 mixing ratio fell from about 15 ppbv to the instrumental detection limit of less than I ppbv in a timespan of about 24 hours. Mixing ratios of alkanes and ethyne decreased concurrently with the O3 decrease. Ancillary data suggested that this was essentially due to chemical reactions only, most probably involving halogen atoms. The hydrocarbon concentrations from the onset of O3 decrease until its virtually complete depletion are used in a first order kinetics analysis to calculate the concentrations of CI and Br atoms that are required to explain these observations. The CI atom concentration is calculated to be 7.5 x 10 4 molec.cm '3. Such a concentration is near the upper limit of earlier estimates, but cannot explain the observed decay of ethyne. Assuming the deficit to be due to bromine atom chemistry, the estimated Br atom concentration is 1.4 x 107 molec.cm '3. The ethyne mixing ratio continued to decrease after virtual total O3 depletion suggesting that Br atoms persisted when O3 was depleted. Hence it is postulated that the depletion of total gaseous mercury (TGM) which terminates upon virtual complete O3 depletion is due to a reaction between gaseous mercury and the BrO molecule.