Plume Chemistry Research Articles

Modeling study of the potential importance of heterogeneous surface reactions for NO x transformations in plumes

A parametric model of gas-particle surface reactions is incorporated into a reactive plume model and used to assess the potential importance of heterogeneous surface reactions on gas phase plume chemistry. Heterogeneous loss of the following species is found to be potentially significant: H 2O 2, PAN, NO 3, N 2O 5, OH, HO 2 and in cold weather HO 2NO 2. This simple model is unable to account for equilibrium/capacity effects in the condensed phase and therefore cannot be used for SO 2 and HNO 3 reaction with aerosol surface.

Dispersion limitations of oxidation in power plant plumes during long-range transport

During the atmospheric transport of combustion-generated emissions of SO2 and NO from point sources, the kinetics of oxidation processes are of particular importance in determining the pattern of subsequent wet and dry deposition because oxidation products such as sulphate aerosol and nitric acid may have deposition characteristics totally different from those of primary emissions. Modelling studies1 have indicated the importance of the ambient air composition and of the dispersion rate on chemistry within plumes during the early stages of transport from point sources, and the important role of mixing in determining oxidant concentrations, particularly ozone, has been demonstrated in near field measurement programmes2–5. It has been generally assumed (see ref. 5) that the significant consequences of dispersion are confined to the early stages of long-range transport and observations to date (see refs 5, 6) indicate that the strong influence of dispersion on plume chemistry is exerted over distances <100 km from source. We report here results of measurements made by an instrumented aircraft of the chemistry within a labelled plume on a trajectory over the North Sea which indicate that oxidation of plume material may be limited by dispersion at distances of at least 650 km.

Photochemical ozone formation from petroleum refinery emissions

Atmospheric emissions from the Marathon oil refinery at Robinson, Illinois were investigated during June and July 1977. Surface and aerial measurements were used to provide an integrated, three dimensional monitoring network. Concentrations of ozone, oxides of nitrogen, sulfur dioxide, methane, carbon dioxide, individual non-methane hydrocarbons and halocarbons were recorded on a routine basis. In addition, meteorological parameters such as wind speed, wind direction, solar radiation and mixing height were also measured. The field monitoring study focused on three major areas: 1. (1) characterization of gaseous components within the refinery effluent, especially nonmethane hydrocarbons and nitrogen oxides; 2. (2) natural sunlight bag irradiation experiments to examine ozone forming potential of refinery emissions and 3. (3) aerial measurements of changes in plume chemistry during the first six to eight hours of transport. Results indicate levels of hydrocarbons and nitrogen oxides were elevated downwind of the refinery. Concentrations within the effluent exceeded background values by as much as 300- and 10-fold, respectively. Irradiations of captured refinery emissions suggest excess photochemical ozone can be produced in the first 6 h, with amounts varying according to NMHC/NO x , ratios and initial NMHC concentrations. Real-time measurements on board the aircraft documented instances of ozone buildup in the refinery plume as it drifted downwind.

On the treatment of point source emissions in urban air quality modeling

This paper presents the development and evaluation of an urban air quality model, the Plume-Airshed Reactive-Interacting System (PARIS), that is capable of providing a detailed treatment of large point source emissions. The PARIS model treats these large point sources by embedding one or more reactive plume models into the Systems Applications urban airshed model, which is a three-dimensional gridded model governed by the atmospheric diffusion equation. These embedded reactive plume models are used to decribe the chemistry and dynamics of large point source plumes and their interaction with the ambient urban environment. When the plume size becomes comparable to the airshed model grid cell size, a subgrid scale description is no longer necessary and the plume material is mixed into the airshed model grid cells. For purposes of evaluation and comparison, the Systems Applications urban airshed model and the PARIS model were applied to the St. Louis urban area for a one-day simulation and to the South Coast Air Basin (Los Angeles area) for a two-day simulation. Overall absolute errors between predictions and observations for the urban airshed and PARIS model simulations are on the order of 40–50% for O 3 and NO 2 concentrations. The overall differences in absolute errors between airshed and PARIS model predictions are between 1 and 5 %; the difference in overall model performance resulting from the PARIS model subgrid scale treatment of point sources is well within measurement uncertainties for both O 3 and NO 2 concentrations. These results indicate that for these two applications, detailed treatment of large point sources with the PARIS model has little effect on overall model performance. However, the model can provide information necessary for the study of the impact of individual point sources located in an urban environment.

A model of sulfate aerosol dynamics in atmospheric plumes

The evolution of atmospheric aerosols is currently a subject of concern because of its relationship to environmental issues. Recently, a rigorous approach for modeling the dynamics of a sectional aerosol distribution has been developed by Gelbard, Tambour and Seinfeld (1980) J. Colloid Interface Sci., 76, 541–556. This paper makes use of this approach and extends it through the presentation of a mathematical model that describes advective transport, turbulent diffusion, gas-phase chemistry and aerosol dynamics in atmospheric plumes. This mathematical model incorporates the Reactive Plume Model, which is a Lagrangian model used to describe plume dynamics consisting of six contiguous cells that expand as the plume is dispersed by atmospheric turbulence. It assumes a Gaussian distribution of the plume arid takes into account interactions with the ambient air. The mathematical model also incorporates the Carbon-Bond Mechanism to model the gas-phase chemistry, which involves 73 reactions among 36 chemical specks. The aerosol population distribution for this model is represented by means of seven sections that have a particle diameter range of 0.01–2.15 μm. Equations describing aerosol dynamics are derived from the classical General Dynamic Equation (CDE) for a sectional aerosol distribution. The dynamic processes described in the model include inter- and intra-sectional coagulation, condensation of acid sulfate or ammonium sulfate and heterogeneous oxidation of sulfur dioxide (SO 2) in each section, as well as new-particle formation in the lowest section. Condensation is diffusion-limited and new-particle formation is estimated from monomer balance theory. Heterogeneous oxidation of SO 2 in the aerosol phase is parameterized by means of a pseudo-first-order chemical reaction. The aerosol dynamics module is evaluated with smog chamber data obtained for an aerosol-H 2SO 4-H 2O system. Aerosol plume model predictions are compared with airborne measurements obtained from the plume of the Navajo power plant on four different days during the VISTTA program, at downwind distances ranging from 25 to 88km. Important characteristics of aerosol dynamics are well described by the model. Secondary aerosol formation is most apparent in the 0.01–0.1 μm size range. Maximum predicted SO 2 homogeneous oxidation rates are 0.5 and 0.6 % h −1 for the summer and winter cases, respectively. Sensitivity studies performed with the aerosol plume model showed that background hydrocarbon concentrations, relative humidity and photolysis rates affect secondary aerosol formation most, whereas atmospheric stability has little effect.

Application of the mixing-reaction in series model to NO x-O 3 plume chemistry

The mixing-reaction in series model developed by Ghodsizadem (1978) is successfully applied to the study of NO oxidation in the near-source portion of the Potomac Electric Company's Morgantown, Maryland power plant plume. The model employs a single parameter. With initial conditions consistent with the plume data measured by Davis et al. (1974) and utilizing the mixing parameter estimated from the study by Shu et al. (1978), the predicted temporal profiles of [NO 2]/[NO], [NO 2]/([NO] + [NO 2]), in-plume [NO] and [O 3], and fraction of NO remaining are consistent with field study data. In addition, the model predicts large deviations from the photostationary state in the near-source portion of the plume, also consistent with field study data. In the far field region of this plume ( t $ ̆ 20 min ), the mixing processes are essentially complete over much of the plume cross-section.

SMOG chamber studies of NO x chemistry in power plant plumes

Smog chamber simulations have been conducted in a 17m 3 irradiation chamber with the purpose of identifying the effects of five independent variables on the transformation rates and product distributions of nitrogen and sulfur species in dilute power plant plumes. The study was designed to simulate the conditions in a plume starting at the point where half the NO has been oxidized to NO 2, where the plume will have been extensively diluted with background air containing hydrocarbons and ozone. The variables studied include: (1) plume hydrocarbon/NO x ratio; (2) composition of organics in the diluting air; (3) NO x/SO 2 ratio; (4) relative humidity; (5) presence of pre-existing acid sulfate aerosol. The starting concentrations and ratios of plume constituents were based on actual plume data. The results of the study are presented in terms of the impact of the independent variables on the extent of NO x conversion to products, the rate of NO x and SO 2 transformation to products and the relative distribution of gaseous and aerosol nitrate products. Briefly, the NO x transformation rate is found to be dependent on hydrocarbon composition, hydrocarbon/NO x ratio and relative humidity. The rates are essentially independent of SO 2 concentration or the presence of pre-existing H 2SO 4 aerosol surface. The SO 2 transformation rate appears to be independent of all five independent variables. The distribution of the nitrate products, nitric acid, peroxyacetyl nitrate and paniculate nitrate is a function of HC composition, HC/NO x ratio and irradiation time. The effects of HC composition and HC/NO x ratio decrease at the longer irradiation times characteristic of transport conditions.

Sulfur chemistry in smelter and power plant plumes in the western U.S.

This paper summarizes the results from studies of SO 2(g) to particle conversion in the plume of a copper smelter and two coal fired power plants located in the Great Basin desert region and an oil fired power plant located on the California coast. Daytime formation of H 2SO 4 from SO 2(g) is dominated by a reaction which is first order in SO 2(g) and is temperature dependent, the rate of reaction increasing with increasing temperature. Neutralization of the H 2SO 4 is limited only by the rate of introduction of basic material from ambient air. NH 3 is not the principal base present except on the California coast. Metal oxides and carbonates (e.g., CaCO 3) are the predominant bases present in the inland desert areas. Two different classes of aerosol S(IV) compounds are formed from the interaction of SO 2(g) with participate matter, organic S(IV) species which can hydrolyze to give sulfite and inorganic S(IV) complexes. The inorganic species predominate in smelter plumes while formation of both the inorganic and the organic S(IV) compounds occurs in plumes from combustion of fossil fuels. Formation of the inorganic S(IV) complex is equilibrium controlled and is favored by high SO 2(g) and soluble aerosol Fe and Cu concentrations and by low aerosol acidity. Formation of the organic S(IV) compound follows first order in SO 2(g) reaction kinetics with the rate being inversely proportional to absolute humidity. The relative amounts of sulfate and the two classes of S(IV) compounds are dependent on the ambient temperature and humidity. Formation of the organic S(IV) compound predominates under cold dry conditions while formation of sulfate predominates when the air mass is warm and moist.

Generation of secondary pollutants in a power plant plume: A model study

A plume model is developed where chemistry and meteorology of the boundary layer interact with a power plant plume which is given a spatial resolution in the cross wind direction. Ozone bulges are formed after 2 1 2 –3 h or more, with excess ozone 10–20 % above ambient levels in fair weather during summer for a plume comparable to the St. Louis Labadie power plant plume. The chemical activity peaks first on the plume fringes, later close to the central axis. Hydroxyl exceeds 13 × 10 6 molecules cm −3 within the plume after a few hours and the corresponding SO 2 to sulphate conversion rate ranges between 1 and 5%h −1. Nitric acid formation exceeds sulphuric acid formation during developed stages of the plume. Ambient emissions of nitrogen oxides and hydrocarbons representative for heavily populated areas tend to reduce the relative size of the ozone bulge compared to cases with lower emissions, and medium size power plants give rise to more excess ozone than larger plants. The ozone bulge disappears when the solar radiation is substantially reduced. The fate of the HSO x radicals and its involvement in odd hydrogen regeneration is essential in the understanding of the plume chemistry.

Effects of a coal-fired power plant and other sources on southwestern visibility (interim summary of EPA'S project VISTTA)

VISTTA (Visibility impairment due to Sulfur Transport and Transformation in the Atmosphere) is a cooperative program involving numerous government agencies, private companies, and universities. † † Participants include Meteorology Research, Inc. (MRI), Systems Applications, Inc. (SAI), Washington University (WU), U of Minnesota (UM), U of Washington (UW), U of California at Los Angeles (UCLA), Washington State U (WSU), U of Vienna (UV), Harvey Mudd College (HMC), U of California at Davis (UCD), EPA Las Vegas (EMSL) (EPA-LV), and Salt River Project (SRP). This paper summarizes the measurements and the results to date of the summer and winter, 1979, VISTTA plume measurement programs conducted near the Navajo Generating Station (NGS), Page, Arizona. During the program, ground and airborne measurements of aerosol size distribution, chemistry and optical properties, as well as gaseous reactant concentrations were made in the plume and in background air. Extensive regional and plume telephotometer measurements, airborne measurements along telephotometer site paths, background meteorological measurements, and source aerosol and chemistry measurements were also made. Various types of visibility measurements were compared with one another and with calculations of light extinction made using aerosol and NO 2 data. The measured plume optical effects were compared to those predicted using the EPA-SAI plume visibility model (PLUVUE). The results of the study to date indicate that: • For the NGS plume, under most lighting and viewing conditions, NO 2 dominates the blue light extinction and brown coloration due to the plume. • For distances up to 100 km or more for power plants like NGS, secondary aerosol formation can be ignored in visibility models under the dry conditions studied. • Widespread areas of elevated aerosol concentrations were documented in the southwest due to long range transport from the southern California area, and to wild fires. Other causes of regional haze are known to exist but were not documented in this study. • Evaluation of the chemistry, aerosol growth, and optics components of the PLUVUE plume visibility model showed predictions to be in reasonable agreement with the measurements. More uncertainty was encountered with the diffusion component. A set of nine reactions among NO, NO 2, O 3, O 2, SO 2, OH, H 2O, and O('D) was found to adequately simulate the plume chemistry for the clean dry background conditions at NGS.

Comparison of the observed and predicted visual effects caused by power plant plumes

One of the objectives of the June–July and December 1979 E.P.A.-VISTTA field programs was to obtain the data necessary to evaluate the components of the EPA/SAI plume visibility model. The data were obtained through a coordinated set of measurements of specific power plant emissions, meteorological conditions, plume concentrations measured by an aircraft and through telephotometer measurements of the visual effects of the plume. This paper presents a comparison of measurements obtained between 4 and 32 km downwind from the plant with model predictions. The various components of the plume visibility model were evaluated independently and it was found that the greatest uncertainties in the model predictions are in the diffusion module, which has the limitations associated with all Gaussian diffusion models. The chemistry module describes plume chemistry well in a clean background atmosphere; however, the rate of NO-to-NO 2 conversion is slightly overpredicted in the model. Predicted secondary aerosol formation is negligible. The optics module of the visibility model was evaluated by predicting the optical effects of the plume on the basis of the airplane-measured plume concentrations. These calculations were compared with the ground-based telephotometer measurements. The optics module tends to slightly overestimate the plume visual effect; the average absolute relative errors in measurements of the plume/sky intensity ratio are 6.0, 6.4, 3.0 and 4.8% at 405, 450, 550 and 630 nm, respectively. For contrast values below − 0.06, the contrast predicted by the optics module is within a factor of 2 of the measured values. A major uncertainty in the data is found in the degree of alignment between the airplane and telephotometer measurements. The overall evaluation of the plume visibility model was carried out with 20 sets of measurements. It was found that the model tends to overestimate the visual effect of the plume. The average absolute relative errors in the plume/sky intensity ratio are 9.7, 10.8, 4.7 and 3.2% at 405, 450, 550 and 630nm, respectively. Sensitivity studies in which NO x and primary paniculate emissions were reduced show that visibility impairment is mainly a result of plume discoloration caused by NO 2 light absorption.

Plume chemistry studies at a northern Alberta power plant

Plume chemistry studies at a northern Alberta power plant

Ambient Air Measurements of Petroleum Refinery Emissions

An ambient air monitoring program to characterize airborne emissions from the Exxon petroleum refinery at Benicia, California was conducted during September 8–22, 1975. Ground level sampling facilities and an instrumented aircraft provided an integrated, three-dimensional monitoring network. Measurements made during the study included ozone, oxides of nitrogen, methane, carbon monoxide, individual C2-C6 hydrocarbons, halocarbons, condensation nuclei, visual distance and various meteorological parameters. The study focused on three major areas: (1) the characterization of gaseous components within the refinery effluent, especially non-methane hydrocarbons and ozone, (2) natural sunlight bag irradiation experiments to determine the ozone forming potential of refinery emissions, and (3) an investigation of changes in plume chemistry as refinery emissions were transported downwind.

Plume chemistry studies at a northern alberta power plant

The plume from the GCOS power plant chimney near Fort McMurray, Alberta was sampled by helicopter during a total of four weeks in February and June, 1977, with the primary aim of studying the rate of SO 2 oxidation to sulfate particulates under various meteorological conditions. A double-filter system was used for the rate studies, and continuous SO 2 and O 3 analysers were also on board for some of the flights. The atmospheric temperature and relative humidity at plume height varied between −13 and 23°C, and 40 and 95% respectively. The field study also covered relatively large changes in solar intensity. The SO 2 oxidation rate was found to be low during the February and early morning June flights — typically, less than 0.5% h −. Later in the day in June, appreciable oxidation was observed (approx. 1–3% h −). An ozone “bulge” was also noted downwind in the plume during several of these latter flights. The results suggest that photochemical processes play an important role in SO 2 oxidation for this power plant plume.

Reactions of ozone and nitrogen oxides in power plant plumes

Results are presented of airborne measurements taken in the plumes of two coal and two gas-fired power plants. Measurements were made of the concentrations of NO, NO 2, O 3 and SO 2, temperature, relative humidity, and ultra-violet radiation. Ozone concentrations exceeding those of the surrounding ambient air were never found in these plumes, which were observed out to distances of 90 km (4 hours travel time) from the stacks. Analysis of the plume chemistry suggests that, over distances and time scales within which plumes are differentiable from background (the “near-field”), the chemistry is commonly controlled by the rates at which the plumes mix with the ambient air, rather than by chemical kinetics. Consequently, on those scales, the rates of conversion of NO to NO 2 are slow and the NO 2/NO ratios are small (the highest ratio measured was 4.3). This analysis is consistent with the absence of observable ozone generation in the “near fields” of the power plant plumes studied.

Trace Gas Analysis of Power Plant Plumes Via Aircraft Measurement: O 3 , NO x , and SO 2 Chemistry

The gaseouis plume from an isolated 1000-megawatt power plant was systematically examined from a single engine aircraft to determine the extent to which NO(x) and SO(2), chemistry occurs as a function of distance. The concentrations of ambient ozone, water vapor, and hydroxyl free radicals are indicated to be of major importance in defining the chemistry of power plant plumes during summertime conditions.