Climatic conditions linked to high PM10 concentration in a bi-national airshed: Nogales (Arizona, USA, and Sonora, Mexico)

Abstract

Traditional particulate matter (PM) studies focus on atmospheric transport and source identification. Focusing on a problematic airshed in southwestern North America, we analyzed atmospheric characteristics and hydroclimatic conditions leading to high concentrations of PM most representative of dust (PM10). The bi-national airshed of Nogales (Arizona, USA and Sonora, Mexico), has been historically characterized by high PM10 concentrations, which tend to be much higher on the Sonora side. Concentrations in greater Nogales tend to be highest in fall and winter and lowest in summer, despite climatologically moister soil conditions in fall and winter. Within the fall, winter, and spring seasons, days of high and low PM10 concentration were primarily distinguished by the condi- tion of the atmosphere, with less emphasis on soil moisture. However, when PM10 concentrations were high, soil moisture was most important in discerning days of very high concentrations on the Arizona side of the border during the most problematic seasons of fall and winter. This was not the case on the Sonora side. Furthermore, drier soil conditions were linked to anomalies in PM10 on the Arizona side of Nogales that were higher than the corresponding anomaly on the Sonora side. The generation of PM on the Sonora side is less reliant on dry soil than it is on the Arizona side, indicating a higher level of anthropogenic dust production on the Sonora side.