Modeling ozone concentrations

[1] Detailed description of the distributions and seasonal trends of atmospheric nitrogen compounds is of considerable interest given their role in formation of acidic substances, tropospheric ozone and particulate matter and nutrient loading effects resulting from their deposition to sensitive ecosystems. While the oxidized nitrogen species have received considerable research and regulatory attention over the past several decades, little effort has been devoted toward quantifying the atmospheric budgets of reduced nitrogen compounds (NH x ) associated with emissions of ammonia. The Regional Acid Deposition Model is enhanced to include detailed treatments of the physical and chemical processes regulating the fate of ammonia emissions and to model the interaction and chemical and thermodynamic coupling between atmospheric NO x -SO x -NH x species. To account for uncertainties in magnitude and seasonal variation of ammonia emissions, regional seasonal correction factors for ammonia emissions in the eastern United States are developed through successive model applications and comparison with measurements from regional networks of ambient concentrations and deposition amounts of various species. The resulting ammonia emissions show a distinct seasonal cycle with a maximum in summer followed by spring, fall, and winter. Our calculations suggest that the range between NH 3 emissions during the cool and the warm season is a factor of 3-4. Correlations between model predicted ambient levels, gas/particle partitioning, and deposition amounts with measurements show good agreement on both an annual and seasonal basis with R 2 in the 0.4-0.7 range for most species examined. Both model calculations and measurements indicate that during winter, large portions of the eastern U.S. are characterized by aerosols that are fully neutralized. Our model calculations for emission scenarios representative of the late 1980s-early 1990s period also indicate that reduced nitrogen species contribute 47(±8)% of the total nitrogen wet deposition in the eastern U.S.; this is in good agreement with 43(±9)% inferred from deposition measurements. These comparisons suggest that the model can capture the spatial and seasonal variability in distributions of various model species, the chemical interactions between reduced and oxidized nitrogen compounds in the troposphere, and the compositional characteristics of inorganic aerosol mass in the region.INDEX TERMS: 0345 Atmospheric Composition and Structure: Pollution-urban and regional (0305); 0365 Atmospheric Composition and Structure: Troposphere-composition and chemistry; 0368 Atmospheric Composition and Structure: Troposphere-constituent transport and chemistry; KEYWORDS: ammonia, aerosols, wet deposition, atmospheric modeling, atmospheric nitrogen Citation: Mathur, R., and R. L. Dennis, Seasonal and annual modeling of reduced nitrogen compounds over the eastern United States: Emissions, ambient levels, and deposition amounts,

Section: Comparison Of Model Predictions With Measurementssupporting

confidence: 61%

Seasonal and annual modeling of reduced nitrogen compounds over the eastern United States: Emissions, ambient levels, and deposition amounts

Mathur

Dennis

2003

“…We therefore restrict our 10,823 comparison to afternoon conditions and compare 0 3 mixing ratios averaged from 1 to 5 p.m. EST for the last 3 days of model simulation. In using the AIRS ozone network data, caution must also be taken in making comparisons since the model predicts grid averaged quantities, and there is some concern about how representative a particular measurement is for a larger area [Schere, 1988]. Also, measurements taken in or near urban areas, which comprise a significant fraction of the total data, may be seriously influenced by local chemistry such as fitration effects by locally emitted NO.…”

Section: Results Of the Model Studymentioning

confidence: 99%

A regional model study of the ozone budget in the eastern United States

McKeen¹,

Hsie²,

Trainer³

et al. 1991

126

In order to better understand the photochemical and meteorological processes controlling regional scale air quality problems such as ozone formation, we have developed a three‐dimensional Eulerian model and applied this model to a high‐pressure period (July 4 to July 7, 1986) over the eastern United States. Meteorological and physical variables from a three‐dimensional primitive‐equation model are used to drive the transport parameters over a grid with 60×60 km2 horizontal resolution, and 15 unequally spaced vertical layers extending from the ground to roughly 15 km. The treatment and incorporation of the dynamic model, the transport model, surface deposition, emission of anthropogenic and natural O3 precursors, the chemical mechanism for 35 individual species, solar radiation and the numerical methods are discussed in detail. Model performance is tested by comparing model predicted O3 concentrations with observations from the U.S. Environmental Protection Agency ozone‐monitoring network. Although a significant correlation between model and observed O3 is found, systematic discrepancies also exist and are discussed in relation to the basic model formulation, and variability in the observed O3. Additionally, a comparison of time‐averaged NOx and anthropogenic nonmethane hydrocarbon (NMHC) concentrations to relatively long term observations provides a qualitative assessment of the model's ability to simulate certain aspects of these O3 precursors from the few available observations. The model is used as a diagnostic tool to analyze various aspects of regional scale O3 formation and the budgets of the primary O3 precursors. Ozone formation over much of the continental model domain is shown to be NOx. limited. On the other hand, for midday NOx levels greater than about 4 or 5 ppbv, O3 formation is generally suppressed because of the low NMHC to NOx ratios (1 to 7) that are characteristic of the emissions inventory. Regional‐scale budget analyses show that very Hide NOx or NMHC is transported to the free troposphere for the high‐pressure conditions of this study and in the absence of a significant subgrid‐scale vertical mixing process (i.e., efficient cumulus transport). We calculate a net turnover time of about 1.5 days for continental O3 below 1800 m with in situ photochemical formation being balanced by photochemical loss and transport off the American continent. The results of this work are intended to serve as a baseline for further model development.

“…The time for computation is reduced by a factor of 25 relative to a 40x40 km 2 model and by a factor of 100 relative to a 20x20 km 2 model. This allows use of a complete chemical mechanism in a large-scale simulation, an important step in developing an accurate regional oxidant model [cL Schere, 1988].…”

Section: We Have Made Comparisons Between Results Of the 8-hourmentioning

confidence: 99%

A regional scale model for ozone in the United States with subgrid representation of urban and power plant plumes

Sillman¹,

Logan²,

Wofsy³

1990

157

A new approach to modeling regional air chemistry is presented for application to industrialized regions such as the contintental United States. Rural chemistry and transport are simulated using a coarse grid, while chemistry and transport in urban and power plant plumes are represented by detailed subgrid models. Emissions from urban and power plant sources are processed in generalized plumes where chemistry and dilution proceed for 8–12 hours before mixing with air in a large resolution element. A realistic fraction of pollutants reacts under high‐NOx conditions, and NOx is removed significantly before dispersal. Results from this model are compared with results from grid models that do not distinguish plumes and with observational data defining regional ozone distributions. Grid models with coarse resolution are found to artificially disperse NOx over rural areas, therefore overestimating rural levels of both NOx and O3. Regional net ozone production is too high in coarse grid models, because production of O3 is more efficient per molecule of NOx in the low‐concentration regime of rural areas than in heavily polluted plumes from major emission sources. Ozone levels simulated by our model are shown to agree with observations in urban plumes and in rural regions. The model reproduces accurately average regional and peak ozone concentrations observed during a 4‐day ozone episode. Computational costs for the model are reduced 25‐ to 100‐fold as compared to fine‐mesh models.