According to the World Health Organization, 235 million people around the world currently suer from asthma, including approximately 25 million in the United States. There is substantial epidemiological evidence particulate matter concentrations and asthma. Based upon county level data from 2001-2014, a spatial panel framework with weights based upon prevailing wind patterns is used to investigate the direct and indirect impacts of PM2:5 concentration levels on asthma hospitalization rates in Pennsylvania. This model controls for population density, precipitation, per capita income, and smoking rate. Results show that PM2:5 concentrations have positive eects on asthma hospitalization rates (both direct and indirect). For example, a one =m3 increase in PM2:5 concentrations throughout all counties in Pennsylvania raises the number of annual asthma hospitalizations by over 400, with 53.8% of this increase occurring due to spillover eects. This study highlights the need for a more accurate impact analysis of ambient air pollution on asthma that re reflects the impacts of both local and neighboring regions' air quality. In the case of asthma hospitalization rates from PM2:5 pollutions, an appropriate wind direction algorithm also is important to identify spillover effects across counties.