A Quantitative Approach to the Traffic Air Quality Problem: The Traffic Air Quality Index

Abstract

The Traffic Air Quality (TAQ) model is a simple tool to estimate traffic fine particulate emissions on roadways (g/km) and can be used for both real-time analysis and for localized conformity analysis (“hot-spot” analysis for nonattainment areas) as defined by 40 CFR 93.123. This paper is a follow-up to a study published earlier regarding the development of the TAQ model. This paper shows how local air quality levels can be a factor in traffic management in nonattainment areas. Similar to the industrial source quotas measured in tons per year, it is proposed that road segments are to be assigned emission quotas (or TAQ indices) measured in pollutant mass emitted per road length (g/km) above which traffic-measures have to be taken to reduce the fine-particulates emissions on such road links. The TAQ model as well as traffic-rerouting measures along with the Intelligent Transportation System (ITS) protocols can be used to have a real-time control of the traffic conditions along expressways to maintain the fine-particulates emissions below the quota assigned per road link and consequently improving the over all local air quality in nonattainment areas.     

An Index of Air Pollution and its Relation to Health

Atmospheric pollution by sulfur oxides is discussed in terms of the sources of the pollutant and the possible methods of control. Possible approaches to control are classified in general categories, including fuel desulfurization, process modifications, and flue-gas desulfurization. Some of the more promising specific possibilities are discussed in relation to the organizations developing them.     

Transient and Frequency Response of Air Quality Monitors

Results of dynamic or transient tests and steady state calibration of carbon monoxide and sulfur dioxide continuous air quality monitors are reported. Standard gases and permeation tubes were used to establish low level concentrations bpth for the steady-state calibration and the dynamic testing. The steady-state calibration was in excellent agreement with results obtained from grab samples of the calibration gas stream taken with standard gas bubblers and analyzed by the West and Gaeke procedure. Such tests have been carried out by other investigators with similar results. The important contribution of this paper lies in the application of dynamic testing techniques developed by the senior author and co-workers to determine the transient and frequency response characteristics of these air quality monitors.     

An Approach to Air Quality Management Standards

The Clean Air Amendments of 1970 impose a stringent set of uniform air quality standards and a rigid timetable for achieving them. Such an approach is open to serious question, since it fails to take account of variations in relevant local conditions. This paper sketches a proposal for a more realistic approach to air quality. It suggests a program of management standards that would reflect the needs and circumstances of particular regions. An institutional framework is outlined that would consider the technical, economic, and social constraints that determine how quickly and how much any area can improve its air quality. The framework would provide the needed flexibility, and would employ a feedback approach that avoids the need to resolve all uncertainties before any progress can be made. At the same time, it would impose a timetable and planning process to assure that all feasible progress in air quality improvement is realized nationwide.     

Air Quality Model Evaluation and Uncertainty

The many advances made in air quality model evaluation procedures during the past ten years are discussed and some components of model uncertainty presented. Simplified statistical procedures for operational model evaluation are suggested. The fundamental model performance measures are the mean bias, the mean square error, and the correlation. The bootstrap resampling technique is used to estimate confidence limits on the performance measures, In order to determine if a model agrees satisfactorily with data or if one model is significantly different from another model. Applications to two tracer experiments are described.

It is emphasized that review and evaluation of the scientific components of models are often of greater Importance than the strictly statistical evaluation. A necessary condition for acceptance Of a model should be that it is scientifically correct. It Is shown that even in research-grade tracer experiments, data Input errors can cause errors In hourly-average model predictions of point concentrations almost as large as the predictions themselves. The turbulent or stochastic component of model uncertainty has a similar magnitude. These components of the uncertainty decrease as averaging time increases.     

A Microcomputer-based Forecasting Model: Potential Applications for Emergency Response Plans and Air Quality Studies

Most atmospheric transport and diffusion models within emergency response systems have very limited physics and are forced to rely on the assumption that wind and turbulence conditions at the time of the release will be representative over the period for which dispersion must be predicted. For releases where the principal concern is about the first few kilometers of travel, such an assumption is appropriate. However, for large accidental releases during stable conditions, the plume may travel for several hours before it is diluted to safe levels and the assumption of persistence may be inappropriate, particularly for transport in complex terrain. Under these circumstances, a model that can forecast changes in wind and turbulence conditions is required. We have installed such a model on microcomputers and tested it in complex terrain near Salt Lake City. One-hour tracer releases produced surface concentrations that remain high for much longer times than that expected based on one hour’ travel time with the mean wind at the source height. Furthermore, relatively large concentrations were found at distances of over 40 km from the source. The model was generally able to reproduce the principal features described by the measurements, although some effects of subgrid scale terrain were missed.     

An Air Quality Approach to Natural Gas Curtailment

A natural gas curtailment procedure designed to improve air quality is proposed and discussed. Computer simulations of this approach, in comparison with an approach which ignores environmental factors, shows that the air-quality approach will produce significant improvements in air quality over the non-environmental approach.     

Using Continuous PM2.5 Monitoring Data to Report an Air Quality Index

Abstract

As stated in 40 CFR 58, Appendix G (2000), statistical linear regression models can be applied to relate PM_2.5 continuous monitoring (CM) measurements with federal reference method (FRM) measurements, collocated or otherwise, for the purpose of reporting the air quality index (AQI). The CM measurements can then be transformed via the model to remove any bias relative to FRM measurements. The resulting FRM-like modeled measurements may be used to provide more timely reporting of a metropolitan statistical area’s (MSA’s) AQI.¹ Of considerable importance is the quality of the model used to relate the CM and FRM measurements. The use of a poor model could result in misleading AQI reporting in the form of incorrectly claiming either good or bad air quality.

This paper describes a measure of adequacy for deciding whether a statistical linear regression model that relates FRM and continuous PM_2.5 measurements is sufficient for use in AQI reporting. The approach is the U.S. Environmental Protection Agency’s (EPA’s) data quality objectives (DQO) process, a seven-step strategic planning approach to determine the most appropriate data type, quality, quantity, and synthesis for a given activity.² The chosen measure of model adequacy is r², the square of the correlation coefficient between FRM measurements and their modeled counterparts. The paper concludes by developing regression models that meet this desired level of adequacy for the MSAs of Greensboro/Winston-Salem/High Point, NC; and Davenport/Moline/Rock Island, IA/IL. In both cases, a log transformation of the data appeared most appropriate. For the data from the Greens-boro/Winston-Salem/High Point MSA, a simple linear regression model of the FRM and CM measurements had an r² of 0.96, based on 227 paired observations. For the data from the Davenport/Moline/Rock Island MSA, due to seasonal differences between CM and FRM measurements, the simple linear regression model had to be expanded to include a temperature dependency, resulting in an r² of 0.86, based on 214 paired observations.     

The Air Quality Health Index and all emergency department visits

Environmental Science and Pollution Research - Through a variety of media formats, the Air Quality Health Index (AQHI) has served as a valuable communication tool for the general Canadian...     

Air Quality Screening Model with Long-Term Averaging

A simple screening model is presented for estimating maximum ground level concentrations of air pollutants from single elevated buoyant sources of emissions. The model, which incorporates plausible error margins, is based on the Gaussian dispersion formula. Maximum longer-term (3, 8, 24 h) concentrations are estimated using a joint probability analysis of the persistence of meteorological worst case events.     

An Efficient Gaussian-Plume Multiple-Source Air Quality Algorithm

The information presented in this paper is directed to air pollution scientists with an interest in applying air quality simulation models. RAM is the three letter designation for this efficient Gaussian-plume multiple-source air quality algorithm. RAM is a method of estimating short-term dispersion using the Gaussian steady-state model. This algorithm can be used for estimating air quality concentrations of relatively stable pollutants for averaging times from an hour to a day in urban areas from point and area sources. The algorithm is applicable for locations with level or gently rolling terrain where a single wind vector for each hour is a good approximation to the flow over the source area considered. Calculations are performed for each hour. Hourly meteorological data required are wind direction, wind speed, stability class, and mixing height. Emission information required of point sources consists of source coordinates, emission rate, physical height, stack gas volume flow and stack gas temperature. Emission information required of area sources consists of south-west corner coordinates, source area, total area emission rate and effective area source height. Computation time is kept to a minimum by the manner in which concentrations from area sources are estimated using a narrow plume hypothesis and using the area source squares as given rather than breaking down all sources to an area of uniform elements. Options are available to the user to allow use of three different types of receptor locations: 1 ) those whose coordinates are input by the user, 2) those whose coordinates are determined by thé model and are downwind óf significant point and area sources where maxima are likely to occur, and 3) those whose coordinates are determined by the model to give good area coverage of a specific portion of the region. Computation time is also decreased by keeping the number of receptors to a minimum.     

A Cost Model for Air Quality Monitoring Systems

A model was developed for remote terminal use to compare the costs of alternate designs of air quality monitoring networks with varying sophistication, ranging from totally manual to completely automated systems. Of special interest is the isolation of manual sample analysis and manual data analysis for comparison with instrumental sensors and automated data processing.

The model allows for 10 levels of sophistication, and 6 were used in sample runs. As many as 50 samplingsite locations, with three different site types, may be specified, and each site type may have any configuration of chemical and/or meteorological sensors. Amortization, labor rates, instrument costs and lifetimes, telephone line charges, and other variables are readily changed by the user as desired.

It was concluded that for systems with fewer than 20–25 sensors, fully automated systems may not be justified on cost alone, at least for producing the same data (hourly) as the manual or semiautomatic systems. (Much more than hourly data is obtained with the automated system, of course.) For larger systems, labor costs put the nonautomated systems at a disadvantage after a few years of operation.     

An Air Pollution Index Based on Sulfur Dioxide and Smoke Shade

First-prize winner in the student paper competition conducted by the Mid-Atlantic States Section of the Air Pollution Control Association was Marvin H. Green, a graduate student at Drexel Institute of Technology and assistant chief of Philadelphia’s Air Pollution Control Section. A condensation of his paper follows.     

An Air Quality Data Analysis System for Interrelating Effects,Standards, and Needed Source Reductions: Part 11. A Lognormal Model Relating Human Lung Function Decrease to O3 Exposure

Forced expiratory volume in 1 second (FEV1) was measured in 21 men exercising while exposed to four O₃ concentrations (0.0,0.08,0.10, and 0.12 ppm). A lognormal multiple linear regression model was fitted to their mean FEV1 measurements to predict FEV1 percent decrease as a function of O₃ concentration and exposure duration. The exercise level used was probably comparable to heavy manual labor. The longest O₃, exposure studied was 6 h. Extrapolating cautiously to an 8-h workday of heavy manual labor, the model predicts that O3 concentrations of 0.08, 0.10, and 0.12 ppm would decrease FEV1 by 9,15, and 20 percent, respectively.     

Recording the Response of Plants to Various Air Pollutants

A discussion of the methods used to determine the most economic design of chimney for a new thermal power station or large industrial plant is presented, with the objective that ground level concentration of pollutants will be kept at a minimum. Attention is paid to the geography and climatology of the site, with special reference to the frequency and height of inversions and the prevailing wind direction and speed.

A method is illustrated in using a large thermal power station as an example. The maximum sulfur dioxide concentrations at ground level are computed for several chimney heights and gas exit velocities. The values of these sulfur dioxide concentrations, the capital cost of the chimney, the pumping costs, and the gas pressures within the chimney are considered in selecting a suitable chimney height and a gas exit velocity which will meet most economically the stated objective.

The paper deals primarily with chimneys for industrial or power boiler plant of maximum continuous rating greater than 450 million Btu/hr (about 450,000 lbs of steam/hr), or to chimneys serving furnaces burning fuel at a maximum rate greater than 50,000 lbs/hr of coal, or 80,000 lbs/hr of oil. For chimneys serving plant with smaller heat inputs, chimney selection by reference to Clean Air Act 1956, Memorandum on Chimney Heights is suggested.     

The Sensitivity of PM25 Source-Receptor Relationships to Atmospheric Chemistry and Transport in a Three-Dimensional Air Quality Model

ABSTRACT

Air quality model simulations constitute an effective approach to developing source-receptor relationships (so-called transfer coefficients in the risk analysis framework) because a significant fraction of particulate matter (particularly PM_2.5) is secondary (i.e., formed in the atmosphere) and, therefore, depends on the atmospheric chemistry of the airshed. In this study, we have used a comprehensive three-dimensional air quality model for PM_{2 5} (SAQM-AERO) to compare three approaches to generating episodic transfer coefficients for several source regions in the Los Angeles Basin. First, transfer coefficients were developed by conducting PM_2.5 SAQM-AERO simulations with reduced emissions of one of four precursors (i.e., primary PM, sulfur dioxide (SO₂), oxides of nitrogen (NO_x), and volatile organic compounds) from each source region. Next, we calculated transfer coefficients using two other methods: (1) a simplified chemistry for PM_2.5 formation, and (2) simplifying assumptions on transport using information limited to basin-wide emission reductions. Transfer coefficients obtained with the simplified chemistry were similar to those obtained with the comprehensive model for VOC emission changes but differed for NO and SO emission changes. The differences were due to the parameterization of the rates of secondary PM formation in the simplified chemistry. In 90% of the cases, transfer coefficients estimated using only basin-wide information were within a factor of two of those obtained with the explicit source-receptor simulations conducted with the comprehensive model. The best agreement was obtained for VOC emission changes; poor agreement was obtained for primary PM_2.5.