Tuesday, 24 January 2012: 11:45 AM
A Sensitivity Study of Ozone Concentration Under Different NOx and VOCs Emissions in a Street Canyon Using a Chemistry Box Model
Room 339 (New Orleans Convention Center )
The sensitivity of ozone concentration to NOx and VOCs emissions in a street canyon is investigated using a chemistry box model. The chemistry box model includes the carbon bond IV mechanism with 36 gaseous species. The emission rates of NOx and VOCs at the bottom of the street canyon vary from 0.01 ppb s-1 to 0.5 ppb s-1 with intervals of 0.01 ppb s-1 (2500 simulation cases). Three different ventilation rates applied at the top of the street canyon and three different emission ratios of NO to NO2 are considered. It is shown that the ozone concentration decreases with increasing NOx emission rate but increases with increasing VOCs emission rate. By combining both emission effects, the ozone concentration has a positive relationship with the emission ratio of VOCs to NOx. The ozone concentration is more sensitive to the NOx emission rate than to the VOCs emission rate. The sensitivity to NOx emission rate is two to ten times larger than that to VOCs emission rate. An increase in NOx emission rate leads to a decrease in the sensitivity of ozone concentration, whereas an increase in VOCs emission rate leads to an increase in the sensitivity of ozone concentration. Changes in the emission ratio of NO to NO2 affect ozone concentration and its sensitivity. Increasing ventilation rate reduces the difference in ozone concentration between the street canyon and the background. This study shows that the sensitivity of ozone concentration in the street canyon depends not only on the NOx and VOCs emission rates, but also on the ventilation rate and the emission ratio of NO to NO2. This is distinguishable from what can be generalized in typical urban areas.