Dependence of Simulated Tropospheric Ozone Trends on Uncertainties in U.S. Mobile Fleet Emissions.

Abstract:

Long-term surface observations show a rapid increase in background concentrations of ozone since the 1960s. Global chemistry-climate models have difficulties in reproducing this trend, overestimating the mid-century observed concentrations. This suggests that the impacts of ozone on climate and air quality throughout the second half of the 20^th century may be misrepresented in current models.

We use the MACCity emissions inventory constrained by ambient observations to examine the dependence of simulated long-term ozone trends on U.S. land transportation (mobile fleet) emissions of nitrogen oxides (NO_X), carbon monoxide (CO) and volatile organic compounds (VOCs). Two sensitivity simulations are performed using the CAM-Chem chemical transport model, where the U.S. MACCity land transportation sector emissions of either NO or CO and co-emitted VOCs are constrained to the observed NO:CO ratio between 1960-2010. We present results from these sensitivity simulations to quantify the dependence of simulated background tropospheric ozone concentrations on these emissions.