Verification of a mathematical model for aerosol nitrate and nitric acid formation and its use for control measure evaluation

A mathematical model for the formation of atmospheric nitric acid and aerosol nitrate has been developed and employed to study the effect of emission controls. Based on a Lagrangian formulation of the atmospheric diffusion equation, the model computes nitric acid concentrations from a description of daytime photochemical reactions and night-time reactions involving NO_3 and N_2O_5. Ammonium nitrate formation is computed at a thermodynamic equilibrium between HNO_3 and NH_3, and heterogeneous reactions between HNO_3 and preexisting aerosol are considered. The accuracy of the air quality model's predictions is verified by comparison to O_3, NO_2, HNO_3, NH_3, aerosol nitrate and PAN measurements made for this purpose in California's South Coast Air Basin during the period of 30–31 August 1982. Examination of emission control alternatives shows that reduction in NO_x emissions yields a nearly proportional decrease in total inorganic nitrate levels (HNO_3 + aerosol nitrates). Reduction in NH_3 emissions suppresses aerosol nitrate formation, resulting in higher HNO_3 levels. Control of organic species emissions by the amounts expected in Los Angeles in future years causes a partial shift away from PAN formation toward greater production of HNO_3. Emission control strategies can be formulated that include a combination of controls on NO_x organic gases and NH_3 emissions that will achieve a greater reduction in HNO_3, aerosol nitrate and O_3 levels than a strategy predicated on control of only a single precursor species

Dry deposition of nitrogen containing species

Nitrogen oxides (NO_x) emissions and the oxidation products formed by photochemical interactions in the atmosphere are responsible for a significant fraction of both dry and wet acid deposition fluxes. In his paper a vertically-resolved, Lagrangian trajectory model is used to predict the diurnal variation of: NO, NO_2, NO_3, HONO, HONO_2, HO_2NO_2, RONO, RONO_2, RO_2NO_2, N_2O_5 and PAN over an urban airshed. Particular attention is given to the fate of nitric acid and its reaction with gaseous ammonia to form, aerosol phase, ammonium nitrate. A simple model for estimating the deposition fluxes of these species is also presented. A study of the fate of nitrogen oxides emissions, in the South Coast Air Basin of southern California, is used to illustrate the procedures

Ozone Formation Potential of Organic Compounds in the Eastern United States: A Comparison of Episodes, Inventories, and Domains

Direct sensitivity analysis is applied for 3-D assessment of ozone reactivity (or ozone formation potential) in the Eastern United States. A detailed chemical mechanism (SAPRC-99) is implemented in a multiscale air quality model to calculate the reactivity of 32 explicit and 9 lumped compounds. Simulations are carried out for two different episodes and two different emission scenarios. While absolute reactivities of VOCs show a great deal of spatial variability, relative reactivities (normalized to the reactivity of a base mixture) produce a significantly more homogeneous field. Three types of domain-wide relative reactivity metrics are formed for 1-h and 8-h averaging intervals. In general, ozone reactivity metrics (with the exception of those based on daily peak ozone) are fairly robust and consistent between different episodes or emission scenarios. The 3-D metrics also show fairly similar rankings for VOC reactivity when compared to the box model scales. However, the 3-D metrics have a noticeably narrower range for species reactivities, as they result in lower reactivity for some of the more reactive, radical-producing VOCs (especially aldehydes). As expected, episodes and emission scenarios with less radical availability have higher absolute reactivities for all species and higher relative reactivities for the more radical-producing species. Finally, comparing the results with those from a different domain (central California) shows that relative reactivity metrics are comparable over these two significantly different domains

The dynamics of nitric acid production and the fate of nitrogen oxides

A mathematical model is used to study the fate of nitrogen oxides (NO_x) emissions and the reactions responsible for the formation of nitric acid (HNO_3). Model results indicate that the majority of the NO_x inserted into an air parcel in the Los Angeles basin is removed by dry deposition at the ground during the first 24 h of travel, and that HNO_3 is the largest single contributor to this deposition flux. A significant amount of the nitric acid is produced at night by N_2O_5 hydrolysis. Perturbation of the N_2O_5 hydrolysis rate constant within the chemical mechanism results in redistribution of the pathway by which HNO_3 is formed, but does not greatly affect the total amount of HNO_3 produced. Inclusion of NO_3-aerosol and N_2O_5-aerosol reactions does not affect the system greatly at collision efficiencies, α, of 0.001, but at α = 0.1 or α = 1.0, a great deal of nitric acid could be produced by heterogeneous chemical processes. Ability to account for the observed nitrate radical (NO_3) concentrations in the atmosphere provides a key test of the air quality modeling procedure. Predicted NO_3 concentrations compare well with those measured by Platt et al. (Geophys. Res. Lett.7, 89–92, 1980). Analysis shows that transport, deposition and emissions, as well as chemistry, are important in explaining the behavior of NO_3 in the atmosphere

Review of BEIS3 formulation and consequences relative to air quality standards

Issued as final repor

Sensitivity of Air Pollution-Induced Premature Mortality to Precursor Emissions Under the Influence of Climate Change

The relative contributions of PM2.5 and ozone precursor emissions to air pollution-related premature mortality modulated by climate change are estimated for the U.S. using sensitivities of air pollutants to precursor emissions and health outcomes for 2001 and 2050. Result suggests that states with high emission rates and significant premature mortality increases induced by PM2.5 will substantially benefit in the future from SO2, anthropogenic NOX and NH3 emissions reductions while states with premature mortality increases induced by O3 will benefit mainly from anthropogenic NOX emissions reduction. Much of the increase in premature mortality expected from climate changeinduced pollutant increases can be offset by targeting a specific precursor emission in most states based on the modeling approach followed here