Air Quality at Devils Postpile National Monument, Sierra Nevada Mountains, California, USA

Abstract

Ambient concentrations of O_3, PM_(2.5), NH_3, NO, NO_2, HNO_3, SO_2 and VOCs were measured at Devils Postpile National Monument (DEPO) during the summer seasons of 2013 and 2014. The measurements were impacted by the Aspen and Rim Fires in 2013, and the French and King Fires in 2014. While O_3 concentrations were not discernibly perturbed by the fire events, the 70 ppb threshold (8-hour average) corresponding to both the current California Ambient Air Quality Standard (CAAQS) and the new National Ambient Air Quality Standard (NAAQS) was exceeded on five days during 2013, and on 16 days during 2014. The older NAAQS of 75 ppb (8-hour average) was exceeded once in 2013, and six times in 2014. Exceedances of the CAAQS or NAAQS occurred when background sources of O_3 were augmented by regional-scale transport, at higher altitudes, of polluted air masses that had passed through the San Joaquin Valley before arriving at the DEPO site. The 2013 Aspen Fire elevated PM_(2.5) to a maximum hourly concentration of 214 μg m^(-3) and a maximum 24 h mean of 92.7 μg m^(-3), and resulted in 13 exceedances of the 35 μg m^(-3) (24 h average) NAAQS for PM_(2.5). The 2013 Rim Fire increased PM_(2.5) to a maximum hourly concentration of 132 μg m^(-3) and a maximum 24 h mean of 69.6 μg m^(-3), and resulted in two exceedances of the 24 h NAAQS. Concentrations of NH_3 increased during all fires, as did those of NO_2 during the Aspen and Rim Fires. Concentrations of benzene increased substantially during the French Fire.