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We report nocturnal measurements of NO 2 and SO 2 by DOAS within marine vessel plumes that impact an island site close to Vancouver during the summer of 2005. The median NO 2 /SO 2 molar ratio from 17 ship plumes (2.86) is marginally higher than the molar NO x /SO x emissions ratio for both: marine vessel emissions (2.39–2.66) in a 2005 inventory for the region and, “underway” emissions of major ocean going vessels (2.04–2.12) in a related marine inventory. Due to the limited nature of our survey, we conclude that the difference between observations and inventories is not unreasonable. The generally low NO 2 /SO 2 ratios we observe are a direct result of the high sulfur content of marine fuels. Measurement of NO 2 /SO 2 ratios is one way to monitor future changes that will occur when new regulations come into force in the Emissions Control Area (ECA) for North American waters, with restrictions on the sulfur content of marine fuel by 2012.

NO 3 was measured at the Sumas Eagle Ridge Site during the Pacific 2001 Air Quality Study. The average maximum levels ( 30 min average) observed on four nights was 34 pptv . NO 3 at these levels can play a significant role in oxidation of volatile oxidation compounds (VOC), particularly biogenic monoterpenes. N 2 O 5 levels were calculated on two nights presuming that the equilibrium, NO 2 + NO 3 ⇄ N 2 O 5 , was maintained. Peak N 2 O 5 levels were 200– 300 pptv . NO 3 and N 2 O 5 were found to contribute 7–9% of the total gaseous NO y on these two nights. Homogeneous and heterogeneous hydrolysis rates of N 2 O 5 were calculated to estimate the nighttime production of gaseous and particulate nitric acid, respectively. Ignoring losses, the overnight total accumulated production of nitric acid was found to be 1.4– 2.1 μ g m - 3 . In a comparison, it was found that the calculated heterogeneous production of fine particle nitrate can account for most of that which was observed experimentally on the two nights, indicating that this process is significant. Particulate pinonaldehyde measured throughout the study showed a significant night/day enhancement, in contrast to other carbonyls, indicating that NO 3 also plays a role in formation of secondary organic aerosols at the site.

As part of the 1993 Lower Fraser Valley Oxidants Study, measurements of mobile source emission factors were performed in the Cassiar Tunnel on the Trans-Canada Highway to measure the on-road contribution to the ozone-forming precursors (NOx and speciated hydrocarbons) along with CO. Observed emission factors were compared to the Canadian versions of the U.S. Environmental Protection Agency's MOBILE models, MOBILE4.1C and MOBILE5C, to assess uncertainty in the predicted mobile source contributions to the Vancouver emissions inventory. A total of 16 1-h runs were made. The timing of the individual runs was designed to encompass different traffic volumes, driving conditions, and times of day. A total of 24,513 vehicles traversed the tunnel during the study, with approximately 91% light-duty vehicles, 4% heavy-duty spark ignition vehicles, and 5% heavy-duty diesel vehicles. MOBILE5C overpredicted the observed value of CO by ∼2%, NMHC by 24%, and NOx by 13%, while MOBILE4.1C underpredicted the observed values by 36, 29, and 23% for CO, NMHC, and NOx respectively.

The photochemical component of an advanced modelling system for use in pollution control studies is evaluated. Results of a case study for July 1985 in the Lower Fraser Valley region of British Columbia are used to test the performance of the modelling system during an ozone episode. Time series of surface trace pollutant concentrations are used to validate the model prediction. A quantitative analysis of the model errors shows that the modelling system adequately predicts the photochemistry without arbitrary adjustments to the emissions inventory. Improved performance of the ozone forecast would likely be obtained, however, if the non-methane organic compound emissions were increased in urban areas. The mechanistic parameters were shown to be very sensitive to the emissions profile, although the net impact of the parameter changes on ozone production was minor in this case.

The SAPRC90 chemical mechanism module implemented in CALGRID is updated for the specific emissions and applications of the Lower Fraser Valley (LFV) of British Columbia, Canada. The kinetic and mechanistic parameters of lumped VOC reactions recalculated using the LFV emissions profiles are noticeably different from those based on default emissions profiles, indicating the importance of tailoring the parameters to specific regions. The sensitivities of ozone concentrations to total and speciated VOC and NOx emissions as well as to the NO 2 NO x ratios are determined. Significant VOC model species are identified based on the impact of their emissions on ozone formation in the LFV. Of note is the importance of the emissions of a lumped class of aromatics, ARO2, which contains mostly isomers of xylene and trimethylbenzene and is derived chiefly from the use and distribution of gasoline fuels. The ARO2 emissions make the largest contribution of all model VOC species to the ozone levels in the urban plume. The results indicate that reduction of AR02 emissions alone could achieve significant reduction of ozone levels in the LFV. Base case emissions of NOx(NO or NO2) in the LFV contribute negatively to the ozone formation. Any overestimation of NOx or underestimation of VOC in the emissions inventory could cause underestimations of ozone levels by photochemical models.

Hydrocarbon distributions measured in the urban area of Toronto during the Southern Ontario Oxidants Study of 1992 are presented. Comparison is made to hydrocarbon distributions measured in other urban areas. Relative concentrations of olefins were found to be depleted aloft compared to the surface level measurements. Chemical mass balance modelling was used to apportion the measured hydrocarbon distributions at York University and other roadside sites to gasoline based sources. The most dominant contributing source was vehicle exhaust. The relative amount of unburned gasoline at York University was found to be significant in the summer, and higher than that observed there during the winter or at other roadside sites. The relative amount of evaporative emissions (gasoline vapour) apportioned by the CMB model at roadside sites was compared to evaporative emissions predicted by a mobile emission factor model, MOBILE5C. The percentage of gasoline based non-methane hydrocarbons (NMHC) apportioned to gasoline vapour by the CMB model was equivalent within error to the relative amount of evaporative NMHC predicted by the MOBILE5C model for summer temperatures. For winter temperatures, the MOBILE5C model predicted significantly less evaporative emissions than that apportioned by the CMB model. An anthropogenic source of isoprene in the urban area has been proposed and tested. The inclusion of an isoprene flux in the exhaust source profile, consistent with that measured in the Auto/Oil Air Quality Improvement Research Program, results in calculated isoprene concentrations that are in agreement with observed concentrations at roadside sites and at York University in the winter. During summer, the combustion related isoprene can only account for a small fraction of the observed isoprene at downtown sites and at York University, at most 20%.