Robin L. Dennis

NARSTO critical review of photochemical models and modeling

Abstract Photochemical air quality models play a central role in both schentific investigation of how pollutants evlove in the atmosphere as well as developing policies to manage air quality. In the past 30 years, these models have evolved from rather crude representations of the physics and chemistry impacting trace species to their current state: comprehensive, but not complete. The evolution has included advancements in not only the level of process descriptions, but also the computational implementation, including numerical methods. As part of the NARSTO Critical Reviews, this article discusses the current strengths and weaknesses of air quality models and the modeling process. Current Eulerian models are found to represent well the primary processes impacting the evolution of trace species in most cases though some exceptions may exist. For example, sub-grid-scale processes, such as concentrated power plant plumes, are treated only approximately. It is not apparent how much such approximations affect their results and the polices based upon those results. A significant weakness has been in how investigators have addressed, and communicated, such uncertainties. Studies find that major uncertainties are due to model inputs, e.g., emissions and meteorology, more so than the model itself. One of the primary weakness identified is in the modeling process, not the models. Evaluation has been limited both due to data constraints. Seldom is there ample observational data to conduct a detailed model intercomparison using consistent data (e.g., the same emissions and meteorology). Further model advancement, and development of greater confidence in the use of models, is hampered by the lack of thorough evaluation and intercomparisons. Model advances are seen in the use of new tools for extending the interpretation of model results, e.g., process and sensitivity analysis, modeling systems to facilitate their use, and extension of model capabilities, e.g., aerosol dynamics capabilities and sub-grid-scale representations. Another possible direction that is the development and widespread use of a community model acting as a platform for multiple groups and agencies to collaborate and progress more rapidly.

Influence of increased isoprene emissions on regional ozone modeling

The role of biogenic hydrocarbons on ozone modeling has been a controversial is- sue since the 1970s. In recent years, changes in biogenic emission algorithms have resulted in large increases in estimated isoprene emissions. This paper describes a recent algorithm, the second generation of the Biogenic Emissions Inventory System (BEIS2). A sensitivity analysis is performed with the Regional Acid Deposition Model (RADM) to examine how increased isoprene emissions generated with BEIS2 can influence the modeling of elevated ozone concentrations and the response of ozone to changes to volatile organic compound (VOC) and nitrogen oxide (NOx) emissions across much of eastern North America. In- creased isoprene emissions are found to produce a predicted shift in elevated ozone concen- trations from VOC sensitivity to NOx sensitivity over many areas of eastern North America. Isoprene concentrations measured near Scotia, Pennsylvania, during the summer of 1988 are compared with RADM estimates of isoprene and provide support for the veracity of the higher isoprene emissions in BEIS2, which are about a factor of 5 higher than BEIS 1 during warm, sunny conditions.

Effects of nitrogen deposition and empirical nitrogen critical loads for ecoregions of the United States

Human activity in the last century has led to a significant increase in nitrogen (N) emissions and atmospheric deposition. This N deposition has reached a level that has caused or is likely to cause alterations to the structure and function of many ecosystems across the United States. One approach for quantifying the deposition of pollution that would be harmful to ecosystems is the determination of critical loads. A critical load is defined as the input of a pollutant below which no detrimental ecological effects occur over the long-term according to present knowledge. The objectives of this project were to synthesize current research relating atmospheric N deposition to effects on terrestrial and freshwater ecosystems in the United States, and to estimate associated empirical N critical loads. The receptors considered included freshwater diatoms, mycorrhizal fungi, lichens, bryophytes, herbaceous plants, shrubs, and trees. Ecosystem impacts included: (1) biogeochemical responses and (2) individual species, population, and community responses. Biogeochemical responses included increased N mineralization and nitrification (and N availability for plant and microbial uptake), increased gaseous N losses (ammonia volatilization, nitric and nitrous oxide from nitrification and denitrification), and increased N leaching. Individual species, population, and community responses included increased tissue N, physiological and nutrient imbalances, increased growth, altered root : shoot ratios, increased susceptibility to secondary stresses, altered fire regime, shifts in competitive interactions and community composition, changes in species richness and other measures of biodiversity, and increases in invasive species.

Atmospheric Deposition of Nitrogen: Implications for Nutrient Over-enrichment of Coastal Waters

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 (RADM) to coastal shelf waters indicates that 11, 5.6, and 5.6 kg N ha−1 may be deposited on the continental shelf areas of the northeastern U.S. coast, southeast U.S. coast, and eastern Gulf of Mexico, respectively. AD-N approximates or exceeds riverine N inputs in many coastal regions. From a spatial perspective, AD-N is a unique source of N enrichment to estuarine and coastal waters because, for a receiving water body, the airshed may exceed the watershed by 10–20 fold. AD-N may originate far outside of the currently managed watersheds. AD-N may increase in importance as a new N source by affecting waters downstream of the oligohaline and mesohaline estuarine nutrient filters where large amounts of terrestrially-supplied N are assimilated and denitrified. Regionally and globally, N deposition associated with urbanization (NOx, peroxyacetyl nitrate, or PAN) and agricultural expansion (NH4+ and possibly organic N) has increased in coastal airsheds. Recent growth and intensification of animal (poultry, swine, cattle) operations in the midwest and mid-Atlantic regions have led to increasing amounts of NH4+ emission and deposition, according to a three decadal analysis of the National Acid Deposition Program network. In western Europe, where livestock operations have dominated agricultural production for the better part of this century, NH4+ is the most abundant form of AD-N. AD-N deposition in the U.S. is still dominated by oxides of N (NOx) emitted from fossil fuel combustion; annual NH4+ deposition is increasing, and in some regions is approaching total NO3− deposition. In receiving estuarine and coastal waters, phytoplankton community structural and functional changes, associated water quality, and trophic and biogeochemical alterations (i.e, algal blooms, hypoxia, food web, and fisheries habitat disruption) are frequent consequences of N-driven eutrophication. Increases in and changing proportions of various new N sources regulate phytoplankton competitive interactions, dominance, and successional patterns. These quantitative and qualitative aspects of AD-N and other atmospheric nutrient sources (e.g., iron) may promote biotic changes now apparent in estuarine and coastal waters, including the proliferation of harmful algal blooms, with cascading impacts on water quality and fisheries.

Ecosystem services altered by human changes in the nitrogen cycle: a new perspective for US decision making

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 compare the costs of N-related impacts or mitigation using the metric of cost per unit of N. Damage costs to the provision of clean air, reflected by impaired human respiratory health, are well characterized and fairly high (e.g. costs of ozone and particulate damages of

Seasonal NH3 emission estimates for the eastern United States based on ammonium wet concentrations and an inverse modeling method

28 per kg NO(x)-N). Damage to services associated with productivity, biodiversity, recreation and clean water are less certain and although generally lower, these costs are quite variable (<

The next generation of integrated air quality modeling: EPA's models-3

2.2-56 per kg N). In the current Chesapeake Bay restoration effort, for example, the collection of available damage costs clearly exceeds the projected abatement costs to reduce N loads to the Bay (

Ecological effects of nitrogen and sulfur air pollution in the US: what do we know?

8-15 per kg N). Explicit consideration and accounting of effects on multiple ecosystem services provides decision-makers an integrated view of N sources, damages and abatement costs to address the significant challenges associated with reducing N pollution.

Design artifacts in eulerian air quality models: Evaluation of the effects of layer thickness and vertical profile correction on surface ozone concentrations

A printing drum is connected to a shaft in such a manner as to withstand the severe stresses created in the connection therebetween when the drum is operated in a mode of intermittent rotary motion. A hardened external contacting surface on the shaft is plated with a layer of copper, and a hardened internal contacting surface on the drum is shrink-fitted on said external contacting surface to form said connection.

Analysis of radical propagation efficiency to assess ozone sensitivity to hydrocarbons and NO x : 2. Long-lived species as indicators of ozone concentration sensitivity

Abstract The U.S. Environmental Protection Agency is developing a third-generation modeling system, termed Models-3. This paper provides an overview of the concepts behind this effort. The modeling challenge is large and is addressed at two main user groups, regulatory analysts and scientists. New technology and tools from the federal High Performance Computing and Communications Program present an opportunity to effectively address computational constraints and the modeling challenge, simultaneously. Two goals of the Advanced Air Quality Modeling Project are (1) provide an effective decision support system and (2) provide a framework to support the evolvement of models and modeling systems. The information needed for a decision support system is described and its elements are defined. The need to be able to significantly evolve the air quality models is discussed next, followed by the presentation of a general software approach for avoiding modeling system obsolescence. In the final section, key modeling considerations and target capabilities are outlined to show the directions being undertaken to initiate Models-3.