Long-term monitoring of atmospheric deposition in central Arizona-Phoenix, ongoing since 1999

The aims of this study are to examine the magnitude and spatial variability in the concentration and flux of wet deposited NO 3 -N, NH 4 -N, DOC, PO 4 -P, Cl, SO 4 , H + , Ca, Mg, Na, K across the Central Arizona-Phoenix region, including the developed urban core and outlying desert. Also to examine patterns of coarse dry particulate deposition across the study area and provide some minimum estimates on levels of dry deposition of these ions. Particularly, this study was designed to answer the question: 'To what extent are concentrations and fluxes of these ions enhanced at sites within the urban core relative to undeveloped desert sites upwind and downwind of the city'. At the outset, the project included eight wet-dry collectors located to form a transect running approximately W-E across the study area from outlying desert to the west, upwind of the prevailing synoptic wind direction, through agriculture to urban core sites, to two downwind sites in the desert to the east and northeast. Collectors were co-located at sites of Maricopa County or Arizona Department of Environmental Quality monitoring stations wherever possible. Monitoring at most sampling locations ran from 1999 through the mid-2000s when sampling was discontinued at several sites. Sampling continued at the Lost Dutchman State Park, also a Desert Fertilization experiment site with a focus on atmospheric deposition, through 2016. Sampling continues at a site on the Arizona State University Tempe campus that was added to the program in 2009.