Atmospheric dry deposition in the vicinity of the Salton Sea, California—I: Air pollution and deposition in a desert environment

Air pollutant concentrations and atmospheric dry deposition were monitored seasonally at the Salton Sea, southern California. Measurements of ozone (O3), nitric acid vapor (HNO3), ammonia (NH3), nitric oxide (NO), nitrogen dioxide (NO2) and sulfur dioxide (SO2) were performed using passive samplers. Deposition rates of NO3−, NH4+, Cl−, SO42−, Na+, K+ and Ca2+ to creosote bush branches and nylon filters as surrogate surfaces were determined for one-week long exposure periods. Maximum O3 values were recorded in spring with 24-h average values of 108.8 μg m−3. Concentrations of NO and NO2 were low and within ranges of the non-urban areas in California (0.4–5.6 and 3.3–16.2 μg m−3 ranges, respectively). Concentrations of HNO3 (2.0–6.7 μg m−3) and NH3 (6.4–15.7 μg m−3) were elevated and above the levels typical for remote locations in California. Deposition rates of Cl−, SO42–, Na+, K+ and Ca2+ were related to the influence of sea spray or to suspended soil particles, and no strong enrichments caused by ions originated by human activities were detected. Dry deposition rates of NO3– and NH4+ were similar to values registered in areas where symptoms of nitrogen saturation and changes in species composition have been described. Deposition of nitrogenous compounds might be contributing to eutrophication processes at the Salton Sea.