Impacts of Central American Fires on Ozone Air Quality in Texas

Background ozone represents the portion of ozone level in one day that cannot be reduced by local emission controls. One of the important factors causing high background ozone events is wildfires. Satellite observations have documented frequent transport of wildfire smoke from Mexico and Central America to the southern US, particularly Texas, causing haze and exceedance of fine particle matters. However, the impact of those fires on background ozone in Texas is poorly understood. In this study, the effects of the Central America fire emissions in spring (Apr-May) from 2000 to 2013 on high background ozone events in Texas are investigated and quantified. We first examine through back trajectory analysis if any high background ozone days in cities of Texas such as Houston can be traced back to fire events in Central America. The GEOS-Chem global chemical transport model and its nested-grid version over North America are used to simulate the periods of the selected cases studies of Central American fires. Long-large transport of gaseous emissions (NOx, VOCs, and CO) from Central American fires are simulated and background ozone concentrations variations in Texas region due to those fire events are also quantified through the difference in model results with and without fire emissions in Central America. Finally, this study connects those fires and high background ozone events, and also quantifies the contribution of fire emissions from Central America on Texas ozone air quality.