Robin L. Dennis

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[1] Significant uncertainty exists in the magnitude and variability of ammonia (NH3) emissions. NH3 emissions are needed as input for air quality modeling of aerosols and deposition of nitrogen compounds. Approximately 85% of NH3 emissions are estimated to come from agricultural nonpoint sources, which are suspected to have a strong seasonal pattern.(More)
Atmospheric deposition of nitrogen (AD-N) is a significant source of nitrogen enrichment to nitrogen (N)limited estuarine and coastal waters downwind of anthropogenic emissions. Along the eastern U.S. coast and eastern Gulf of Mexico, AD-N currently accounts for 10% to over 40% of new N loading to estuaries. Extension of the regional acid deposition model(More)
Human alteration of the nitrogen (N) cycle has produced benefits for health and well-being, but excess N has altered many ecosystems and degraded air and water quality. US regulations mandate protection of the environment in terms that directly connect to ecosystem services. Here, we review the science quantifying effects of N on key ecosystem services, and(More)
Three probes for diagnosing photochemical dynamics are presented and applied to specialized ambient surface-level observations and to a numerical photochemical model to better understand rates of production and other process information in the atmosphere and in the model. However, care must be taken to ensure that rate and process information is not(More)
This paper discusses the need for critically evaluating regional-scale (~200-2000 km) three-dimensional numerical photochemical air quality modeling systems to establish a model's credibility in simulating the spatio-temporal features embedded in the observations. Because of limitations of currently used approaches for evaluating regional air quality(More)
Unbiased symmetric metrics to quantify the relative bias and error between modeled and observed concentrations, based on the factor between measured and observed concentrations, are introduced and compared to conventionally employed metrics. Application to the evaluation of several data sets shows that the new metrics overcome concerns with the conventional(More)
Significant uncertainty exists in the seasonal distribution of NH3 emissions since the predominant sources are animal husbandry and fertilizer application. Previous studies that estimated bottom–up and top–down NH3 emissions have provided the most comprehensive information available about the seasonality of NH3 emissions. In this study, this bottom–up and(More)
Chemical transport models have frequently been used to evaluate the impacts of emission reductions on inorganic PM2.5. However, such models are limited in their accuracy by uncertain estimates of the spatial and temporal characterization of emissions and meteorology. Site-specific observations can more accurately characterize the distribution of pollutants,(More)
Seasonal and regional variations of primary (OC(pri)) and secondary (OC(sec)) organic carbon aerosols across the continental United States for the year 2001 were examined by a semi-empirical technique using observed OC and elemental carbon (EC) data from 142 routine monitoring sites in mostly rural locations across the country, coupled with the primary(More)
The University of California at Davis (UCD) aerosol module, an internally mixed, sectional aerosol model with dynamic mass transfer between the gas and particle phases, has been coupled to the Community Multiscale Air Quality (CMAQ) model. This paper describes the application of the CMAQ-UCD model to simulate air quality in Tampa, a large city with a(More)