NOx-derived dry deposition fluxes using the Community Multiscale Air Quality Model (CMAQ) (9-13 June 1998) in conjunction with the mesoscale meteorological model MM5. A new land cover classification and updated land cover data were introduced in the model to account for spatial extent and heterogeneity of urban land cover (derived from the land cover map by Stefanov et al. 2001). Adjustments were made in the deposition velocity calculations to consider the adaptation of local plants to the environmental conditions of Central Arizona. CMAQ simulations gave predicted hourly NOx and nitric acid deposition, allowing spatial patterns in NOx deposition to be evaluated for the modeling domain which included the entire Phoenix metropolitan area, along with the surrounding desert and agricultural land. Using a diagnostic model with input data from urban air quality monitoring sites, hourly NO and NO2 dry N deposition fluxes were simulated for the entire year 1998 to ~6 kg ha-1 yr-1. Dry deposition declined during the summer months, due to lower pollutant concentrations and temperature-induced closure of the plant stomata during afternoon hours. To obtain estimates of dry deposition for the whole study area, the results of the diagnostic model were complemented with the CMAQ simulations. Scaling the whole system predictions to account for seasonal variations, along with an addition of 3.5 kg N ha-1 yr-1 for deposited ammonium (as estimated by Baker et al. 2001) and 10% as particulates, the dry deposition flux (kg N ha-1 yr-1) was estimated to be 13.5 for the urban core, 15.0 for the downwind desert and 7.5 for the upwind desert. The dry deposition flux to the entire system was on average approximately 12 kg N ha-1 yr-1. Estimated N deposition to the most exposed agricultural and desert areas was 28-29 kg ha-1 yr-1.
### references
- Baker, L., Hope, D., Xu, Y. et al. Nitrogen Balance for the Central Arizona–Phoenix (CAP) Ecosystem. Ecosystems 4, 582–602 (2001). https://doi.org/10.1007/s10021-001-0031-2
