Toxicological Appraisal of Carbon Monoxide

The draft Technical Report on Air Quality Criteria for Carbon Monoxide shows thorough familiarity with the relevant toxicological studies. The authors selected materials for discussion very judiciously. They present the pertinent information in sufficient detail to permit an independent judgment of its significance, in most instances. The conclusions are firmly based on the information which is presented.     

Carbon Monoxide Levels in Athletes during Exercise in an Urban Environment

ABSTRACT

Gas phase concentrations of individual polycyclic aromatic hydrocarbons (PAHs) were measured in real time in combustion products from a co-flow diffusion flame using laser photoionization (LP) time-of-flight mass spectrometry (TOF/MS). In particular, a naphthalene detection sensitivity of 4 parts per billion (ppb) was demonstrated. The use of calibration mixtures with argon indicated the feasibility of naphthalene detection at about 45 parts per trillion (ppt) at a signal-to-noise (S/N) ratio of 20. This suggests the possibility of low-ppt level detection at a S/N of 1. The novelty of the system is the use of a heated sampling probe and a continuously purged, heated-pulse valve that was positioned close to the ionization zone, thereby allowing the generation of photoions in the high-density region of the sample jet, where concentrations of PAH are high. Because the system developed allows for the real time detection of select species, it represents a useful tool in continuous emissions monitoring (CEM) for environmental compliance as well as direct process control.     

Carbon Monoxide in the Atmosphere

A carbon monoxide analyzer has been developed which is capable of continuous measurement of the carbon monoxide concentration in the atmosphere. The operating principle of the instrument is the reaction of carbon monoxide with hot mercuric oxide followed by the photometric determination of the mercury vapor produced. Oxygenated hydrocarbons and olefins are quantitatively detected. Those normally present are in the ambient atmosphere in low concentrations relative to CO. Hydrogen and methane in the atmosphere do not interfere with the CO analysis. Measurements of atmospheric CO concentrations in California, Greenland, and Oregon seem to indicate that CO content is an air mass characteristic. North Pacific marine air mass concentrations may be as low as about 0.040 parts per million (ppm) CO, while the air mass over continental California seems to be characterized by CO levels of 0.5-1.0 ppm or greater.     

Exposure of Drivers to Carbon Monoxide

Eleven new cars were driven around a 35 km route comprising heavily trafficked roads in and around London, and the concentrations of carbon monoxide inside and immediately outside the vehicles were continuously monitored. Average levels of CO between 12 and 60 parts per million were found inside the cars, and these levels were between 30 and 80% of the external concentrations. The internal levels varied according to external changes but the changes were greatly damped by the buffering effect of the ventilation system. Differences in internal CO levels were more marked between vehicles than for different runs in the same vehicle and were probably due to differences in the ventilation systems.

Blood carboxy-hemoglobin concentrations which would arise from the CO exposures were calculated. Published data suggest that carboxy-hemoglobin concentrations within the range found (1.5-3.0%) would not be expected to produce an adverse effect on health; there are conflicting views as to whether driving performance would be impaired.     

Modeling of Carbon Monoxide Hot Spots

This paper describes the results of a measurement and modeling study of carbon monoxide (CO) concentrations In the proximity of intersections. Analysis for model performance of paired observed and predicted CO concentrations are presented. Two methodologies of pollutant prediction were used: the Intersection Midblock Model (IMM) and a statistical multiple linear regression. The results showed that both methods underpredicted frequently and dispensed results that were site specific. In addition, correlations of IMM predicted concentrations to observed concentrations were poor (typically r² values <0.25). Various explanations for this observation are proposed. The statistical approach exhibited an improved accuracy over that of IMM. However, some of the independent variables used might be difficult to obtain as a routine measurement, and use of a one or two independent parameter model yielded adjusted R² values comparable to the r² values observed with IMM. Based on these results, an Intersection model applicable under a wide range of conditions of traffic, meteorology, and geometry is not available. Research Is needed to develop one, since its use would often be called on in the development of air quality sections of Environmental Assessments or Environmental Impact Statements.     

Vehicle Occupant Exposure to Carbon Monoxide

Abstract

This paper focuses on the auto commuting micro-environment and presents typical carbon monoxide (CO) concentrations to which auto commuters in central Riyadh, Saudi Arabia were exposed. Two test vehicles traveling over four main arterial roadways were monitored for inside and outside CO levels during eighty peak and off-peak hours extending over an eight month period. The relative importance of several variables which explained the variability in CO concentrations inside autos was also assessed. It was found that during peak hours auto commuters were exposed to mean CO levels that ranged from 30 to 40 ppm over trips that typically took between 25 to 40 minutes. The mean ratio of inside to outside CO levels was 0.84. Results of variance component analyses indicated that the most important variables affecting CO concentrations inside autos were, in addition to the smoking of vehicle occupants, traffic volume, vehicle speed, period of day and wind velocity. An increase in traffic volume from 1,000 to 5,000 vehicles per hour (vph) increased mean CO level exposure by 71 percent. An increase in vehicle speed from 14 to 55 km/h reduced mean CO exposure by 36 percent. The number of traffic interruptions had a moderate effect on mean concentrations of CO inside vehicles.     

Carbon Monoxide and Lead-An Environmental Appraisal

Because of the common source, lead and CO values in the atmosphere tend to behave in a similar manner. Thus, diurnal variations in these two pollutants show a pattern related to motor vehicle traffic flow. Also, the exposure to both vary by orders of magnitude with the highest being on the road (in the car) thus setting up special dosage situations. Community sources seem to affect background level at least based on fall-off with distance. There may be a relatively wider exposure of the general population to lead and CO. While the lead levels may not be increasing in the downtown portion of the central city proper, typical central city levels of several years ago may be more diffuse and spread out, thus occurring over increasingly large portions of the community. Similarly, there may be a wider exposure of the population to CO as the levels become more nearly uniformly high over a larger area. In addition, there may be problems of a shorter term exposure to high levels of CO in commuter traffic. This may be of consequence to selected types of drivers or passengers. Finally, it should also be noted that during air pollution episodes, CO levels appear to rise with no data currently available on changes in concomitant ambient lead levels.     

Catalytic Cigarette Filter for Carbon Monoxide Reduction

A comparative study was performed in order to determine the relative accuracy of a gaussian dispersion model. The U.S. EPA’s RAM (Urban) model was chosen to estimate 24-hour average sulfur dioxide concentrations in the Cleveland, Ohio area. Point and area source emissions, along with a background concentration were included in the modeling effort. Projections from the model made at the ambient air stations were compared to measured sulfur dioxide concentrations. A total of 3020 comparisons were performed at 33 monitoring sites. An analysis of the results illustrates that, on a daily basis, the predictions of the model did not reflect actual air quality. The correlation coefficients of the 24-hour comparisons at the monitoring sites varied from a low of —0.121 to a high of 0.541. When the highest and second highest modeled concentrations were evaluated with respect to the highest and second highest measured concentrations, over a period of a year, a more favorable comparison was observed.     

An Urban Diffusion Simulation Model For Carbon Monoxide

A relatively simple Gaussian-type diffusion simulation model for calculating urban carbon monoxide (CO) concentrations as a function of local meteorology and the distribution of traffic is described. The model can be used in two ways: (1) in the synoptic mode, in which hourly concentrations at one or many receptor points are calculated from historical or forecast traffic and meteorological data; and (2) in the climatological mode, in which concentration frequency distributions are calculated on the basis of long-term sequences of input data. For model evaluation purposes, an extensive field study involving meteorological and air-quality measurements was conducted during November-December 1970 in San Jose, Calif., which has an automated network to provide traffic data throughout the central business district. Model refinements made on the basis of the data from this experimental program include the addition of a street-canyon submodel to compensate for the important aerodynamic effects of buildings on CO concentrations at streetside receptors. The magnitude of these effects was underscored by the concentrations measured on opposite sides of the street in San Jose, which frequently differed by a factor of two or more. Evaluation of the revised model has shown that calculated and observed concentration frequency distributions for street-canyon sites are in good agreement. Hour-average predictions are well correlated with observations (correlation coefficient of about 0.6 to 0.7), and about 80 percent of the calculated values are within 3 ppm of the observed hour-average concentrations, which ranged as high as 16 ppm.     

Carbon Monoxide Exposures to Los Angeles Area Commuters

Carbon monoxide exposures to commuters were simulated in a 5-day study in Los Angeles County. Exposures were determined by measuring CO in three vehicles as they traveled typical commuter routes. The data collected during this study include measurements of vehicle speed and CO measurements in the interior and exterior of the three vehicles during the morning and evening peak traffic periods. In addition, hourly averaged CO measurements were taken from eight south coastal Air Quality Management District fixed-site monitoring stations and six California Department of Transportation vans in the proximity of the commuter routes. These data were used to investigate the relationship of CO exposures to meteorological parameters, fixed-site monitors, and traffic conditions.

The average ratio of interior CO concentrations to exterior CO concentrations was 0.92. Concentrations inside and outside the vehicles remained about the same even when the vehicles were driven with vents closed and windows up. Smoking was not permitted in the vehicles during the study. The average ratio of the hour average CO concentrations in the vehicles to fixed-site measurements was 3.9. However, this ratio decreases with increasing ambient CO levels. Although CO levels in the vehicles frequently exceeded 40 ppm and sometimes exceeded 60 ppm, the hour average CO concentrations did not exceed 35 ppm. Slow moving congested traffic is associated with higher CO levels in the vehicles than a high volume of traffic moving at a steady speed.     

Ambient Carbon Monoxide And Its Fate in the Atmosphere

Carbon monoxide, the most abundant air pollutant found in the atmosphere generally exceeds that of all other pollutants combined (excluding C0₂). An estimated tonnage of >87 X 10⁶ of CO was emitted in the United States from major technological sources alone during 1966. More than 90% of the total CO emitted from fossil fuels is derived from gasoline powered motor vehicles. Other sources of CO include emissions from coal and fuel oil burning, aircraft and open burning. Some CO is also formed by certain vegetation and marine invertebrates (siphonophores). Chemical reactions of CO in the upper and lower atmosphere are discussed. Chemical oxidation of CO in the lower atmosphere by molecular oxygen is very slow. The exact duration of CO in the lower atmosphere is not known with certainty; however, the mean residence time has been variously estimated to be between 0.3 and 5.0 years. In the absence of scavenging processes the estimated world-wide CO emission would be sufficient to raise the’atmospheric level by 0.03 ppm per year, yet the background levels of CO in clean air do not appear to be increasing. Several potential sinks are discussed. Knowledge of the mechanism of process of removal of CO from the lower atmosphere is unsatisfactory; the process, at the present time, cannot be identified with certainty.     

The Need for Representative Ambient Air Carbon Monoxide Sampling

Recent investigations have indicated that ambient air CO measurements may not reflect population exposure to CO. The lack of correlation may be due to improper siting of CO instruments, improper interpretation of air quality data, or both. Studies of population carboxy-hemoglobin levels are evaluated and compared with ambient air data.,

No significant correlation was found between median population COHb levels and reductions in CO concentrations required to meet ambient air standards when calculations used to estimate reductions were based on the second highest 8 hour average. However, calculated reductions based on annual average concentrations and a trend analysis technique correlated significantly with COHb levels in five cities from which both CAMP and COHb data were available.

Studies to determine the nature of the relationship between ambient air CO concentrations and population COHb levels are needed. The differences between the Occupational Safety and Health Act Regulations and the National Ambient Air Standards for carbon monoxide should be scrutinized to determine if a redefinition of the standards or their applicability is warranted. A reevaluation of the controls necessary to make reductions in population COHb burden may be necessary.     

A Numerical Model of Diffusion of Carbon Monoxide near Highways

A numerical model, which can be used to study the dispersion of carbon monoxide emissions from automobiles traveling on a highway, is described. The model Is based upon the semi-empirical equation of turbulent diffusion. The performance of the model has been tested using carbon monoxide concentration data obtained near highway 401 in the city of Toronto, Canada.     

An Examination of the Intra-SMSA Distribution of Carbon Monoxide Exposure

Although fixed-site monitoring data have been used to estimate the spatial pattern of human exposure, the intra-urban distribution of actual exposure has not been documented. This paper used the data collected during the Environmental Protection Agency’s (EPA) field investigation of personal exposure to carbon monoxide (CO) to investigate the nature of the distribution of CO with respect to residential location In the Washington, D.C. SMSA. Dot-distribution maps and analysis of variance were used to document the spatial pattern of individual-level in-home CO concentrations. The results show sampled individuals living in the SMSA center are exposed to statistically significantly higher levels of CO than are those living in the suburbs. The most important Implications of this work are for exposure modeling. Further investigation is needed to determine whether incorporation of a geographic component will improve exposure prediction.     

活性炭吸附有机蒸气过程中的初始浓度测定

以PTA生产尾气为实验体系，讨论了在活性炭对有机气体动态吸附过程中，有机气体初始浓度的三种测定方法，即气相色谱法、吸附称量法和气体方程计算法。结果得出，吸附称量法误差最小，其次是气体方程计算法，误差最大的是气相色谱法。