Personal carbon monoxide exposures of preschool children in Helsinki, Finland—comparison to ambient air concentrations

The associations of personal carbon monoxide (CO) exposures with ambient air CO concentrations measured at fixed monitoring sites, were studied among 194 children aged 3–6 yr in four downtown and four suburban day-care centers in Helsinki, Finland. Each child carried a personal CO exposure monitor between 1 and 4 times for a time period of between 20 and 24 h. CO concentrations at two fixed monitoring sites were measured simultaneously. The CO concentrations measured at the fixed monitoring sites were usually lower (mean maximum 8-h concentration: 0.9 and 2.6 mg m⁻³) than the personal CO exposure concentrations (mean maximum 8-h concentration: 3.3 mg m⁻³). The fixed site CO concentrations were poor predictors of the personal CO exposure concentrations. However, the correlations between the personal CO exposure and the fixed monitoring site CO concentrations increased (−0.03–−0.12 to 0.13–0.16) with increasing averaging times from 1 to 8 h. Also, the fixed monitoring site CO concentrations explained the mean daily or weekly personal CO exposures of a group of simultaneously measured children better than individual exposure CO concentrations. This study suggests that the short-term CO personal exposure of children cannot be meaningfully assessed using fixed monitoring sites.     

The effect of EURO-0 vehicle substitution on polycyclic aromatic hydrocarbon and carbon monoxide concentrations in an urban area

From 1994 to 2003, daily air concentrations of particle-bound polycyclic aromatic hydrocarbons (PAHs) and carbon monoxide (CO) were regularly monitored at two traffic-oriented sampling sites (A and B) in urban Genoa, Italy. The data were used to estimate effects on air quality in real situations due to progressive substitution of EURO-0 vehicles, started in 1993, with less-polluting vehicles (EURO-1, EURO-2), mainly gasoline vehicles with a catalyst. PAH profile classification and diagnostic PAH ratios were used to identify 345 samples of predominantly traffic origin. At both sites, CO and PAH daily concentrations decreased exponentially with time and the apparent half-life values calculated were 6.3 and 5.5 for CO and 3.7 and 3.5 years for PAHs at sites A and B, respectively. At site A, monitored for traffic intensity, multiple regression analyses confirmed that daily PAH and CO concentrations were positively correlated with the number of non-catalytic vehicles estimated to cross this site during sampling and negatively correlated with seasonal variables (air temperature, ozone concentration, relative air humidity). The reduction in air pollution estimated for complete substitution of non-catalytic gasoline vehicles was 89% for BaP, 85% for total PAHs and 69% for CO.     

Climatology and forecast modeling of ambient carbon monoxide in Phoenix, Arizona

We perform a climatology of factors influencing ambient carbon monoxide (CO), in which we examine the relationships between meteorology, traffic patterns, and CO at seasonal, weekly, and diurnal time scales in Phoenix, Arizona. From this analysis we identify a range of potentially important variables for statistical CO modeling. Using stepwise multivariate regression, we create a suite of models for hourly and 8-h ambient CO designed for daily operational forecasting purposes. The resulting models include variables and interaction terms related to anticipated nocturnal atmospheric stability as well as antecedent and climatological CO behavior. The models are evaluated using a range of error statistics and skill measures. The most successful approach employs a two-stage modeling strategy in which an initial prediction is made that may, depending on the forecast value, be followed by a second prediction that improves upon the first. The best models provide accurate daily forecasts of CO, with explained variances approaching 0.9 and errors under 1 ppm.     

The effect of different ventilation modes on in-vehicle carbon monoxide exposure

In-vehicle carbon monoxide (CO) concentration profiles were monitored in a passenger vehicle driven along a heavily traveled route of a commercial/residential area of Beirut, Lebanon, under several ventilation modes. Trips were conducted during morning rush hours in spring and summer time. Concomitant monitoring of car-exterior CO level, ambient CO level and wind speed was also undertaken. The highest mean CO exposure was experienced for the “windows closed, vents closed” and “windows closed, AC on recirculation” ventilation settings, with mean CO levels of 37.4 and 30.8 ppm, respectively, exceeding the 1-h air quality guidelines. The exposure was less significant for other ventilation modes with respective mean values of $10.8–19\mathrm{ppm}$. Mean car-exterior CO levels were lower than the 1-h air quality guidelines, but exceeded the 8-h CO exposure guidelines. Ambient CO levels were low and non-representative of the personal exposure of individuals neither inside nor in the vicinity of road vehicles. In-vehicle CO levels revealed moderate to good correlations to out-vehicle CO levels for ventilation modes allowing for outdoor air intake, and no correlation to ambient CO levels and wind speed. Infiltration as a result of indoor–outdoor air exchange and intrusion from engine combustion/exhaust infiltration constituted the main sources of observed in-vehicle CO levels.     

Interpreting the eight-hour national ambient air quality standard for carbon monoxide

There are two principal approaches to the 8-hour carbon monoxide standard: (1) 8-hour moving averages that culminate with every clock hour, and (2) nonoverlapping averages for consecutive 8-hour intervals. Examination of 1972 data for three example sites (Newark, NJ, Camden, NJ, and Spokane, WA) shows that the maximum and the “second high” control values derived from moving averages can be at least 20% higher than corresponding values detected by the consecutive 8-hour intervals. The natural fluctuation in the time of day when the maximum occurs and the variability in episode length make it doubtful that any framework of consecutive 8-hour intervals can adequately portray the essential characteristics of CO exposure. Prudence recommends choice of the moving 8-hour average as more sensitive to actual maximum levels and to short episodes, more faithful to the body’s integrating response to CO exposure, and more equitable in presenting comparisons among stations with differing patterns of daily variation.     

Evaluation of combustion by-products of MTBE as a component of reformulated gasoline

Methyl tertiary-butyl ether (MTBE) is a gasoline oxygenate that is widely used throughout the US and Europe as an octane-booster and as a means of reducing automotive carbon monoxide (CO) emissions. The combustion by-products of pure MTBE have been evaluated in previous laboratory studies, but little attention has been paid to the combustion by-products of MTBE as a component of gasoline. MTBE is often used in reformulated gasoline (RFG), which has chemical and physical characteristics distinct from conventional gasoline. The formation of MTBE by-products in RFG is not well-understood, especially under "worst-case" vehicle emission scenarios such as fuel-rich operations, cold-starts or malfunctioning emission control systems, conditions which have not been studied extensively. Engine-out automotive dynamometer studies have compared RFG with MTBE to non-oxygenated RFG. Their findings suggest that adding MTBE to reformulated gasoline does not impact the high temperature flame chemistry in cylinder combustion processes. Comparison of tailpipe and exhaust emission studies indicate that reactions in the catalytic converter are quite effective in destroying most hydrocarbon MTBE by-product species. Since important reaction by-products are formed in the post-flame region, understanding changes in this region will contribute to the understanding of fuel-related changes in emissions.     

Weekday/Weekend differences in ambient air pollutant concentrations in atlanta and the southeastern United States

The authors quantified changes between mean weekday and weekend ambient concentrations of ozone (O3) precursors (volatile organic compounds [VOC], carbon monoxide [CO], nitric oxide, and oxides of nitrogen [NOx]) in Atlanta and surrounding areas to observe how weekend precursor emission levels influenced ambient O3 levels. The authors analyzed CO, nitric oxide (NO), and NO, measurements from 1998 to 2002 and speciated VOC from 1996 to 2003. They observed a strong weekend effect in the Atlanta region, with median daytime (6:00 a.m. to 3:00 p.m. Eastern Standard Time) decreases of 62%, 57%, and 31%, respectively, in the ambient levels of NO, NOx, and CO from Wednesdays to Sundays, during the ozone season (March to October). They also observed significant decreases in ambient VOC levels between Wednesdays and Sundays, with decreases of 28% for the sum of aromatic compounds and 19% for the sum of Photochemical Assessment Monitoring Stations target compounds. Despite large reductions in O3 precursor levels on weekends, day-of-week differences in O3 mixing ratios in and near Atlanta were much smaller. Averaging overall O3-season days, the 1-hr and 8-hr mean peak daily O3 maxima on Sundays were 4.5% and 2.3% lower, respectively, than their mean levels on Wednesdays (median of 14 site differences), with no sites showing statistically significant Wednesday-to-Sunday differences. When restricted to high-O3 days (highest 3 peak O3 days per day of week per site per year), the 1-hr and 8-hr Sunday O3 mixing ratios were 11% and 10% lower, respectively, than their mean peak levels on Wednesdays (median of 14 site differences), with 6 of 14 sites showing statistically significant Wednesday-to-Sunday differences. The analyses of weekday/weekend differences in O3 precursor concentrations show that different emission reductions than normally take place each weekend will be required to achieve major reductions in ambient ozone levels in the Atlanta area.     

A simple semi-empirical model for predicting missing carbon monoxide concentrations

Carbon monoxide monitoring using continuous samplers is carried out in most major urban centres in the world and generally forms the basis for air quality assessments. Such assessments become less reliable as the proportion of data missing due to equipment failure and periods of calibration increases. This paper presents a semi-empirical model for the prediction of atmospheric carbon monoxide concentrations near roads for the purpose of interpolating missing data without the need for any traffic or emissions information. The model produces reliable predictions while remaining computationally simple by being site-specifically optimized. The model was developed for, and evaluated at, both a suburban site and an inner city site in Hamilton, New Zealand. Model performance statistics were found to be significantly better than other simple methods of interpolation with little additional computational complexity.     

Combustion of gasolines in premixed laminar flames European certified and California phase 2 reformulated gasoline

Two gasoline qualities, European unleaded certified gasoline (EUCG) and California phase 2 reformulated gasoline (P2 RFG), were analysed. EUCG contained about twice the amount of alkyl benzenes compared to P2 RFG and a large amount of cyclohexane. As a balance, P2 RFG contained higher amounts of isooctane and MTBE. The gasolines were burned in a premixed laminar flame burner at 1 atm and at about stoichiometric fuel/air ratio. The species profiles were measured using on-line GC/MS. About 40 compounds were be detected in the gasoline flames. The EUCG resulted in formation of more reactive and toxic compounds. The combustion profiles of the fuel components showed a similar slope, which suggests that the fuel components burn quite independently of each other. Ethene and propene were the dominating species produced from the two gasolines. Commonly, substantial amounts of higher alkenes were found. Combustion of P2 RFG produced higher amounts of isobutene, propene, propyne, propadiene and methanol compared to combustion of EUCG. The high amount of isobutene is reasonably a result of high concentration of isooctane and MTBE in the fuel. The high amount of methanol formed is probably due to the MTBE present in the gasoline. EUCG produced significantly higher amounts of 1,3-butadiene, which quite likely is formed from the cyclohexane in the fuel. The benzene profiles from both gasolines shows an almost constant level up to 800 microm from the burner surface; this is probably due to formation of benzene from alkyl benzenes.     

Fine particulate matter and carbon monoxide exposure concentrations in urban street transport microenvironments

Personal exposure studies are crucial alongside microenvironment and ambient studies in order to get a better understanding of the health risks posed by fine particulate matter and carbon monoxide in the urban transport microenvironment and for making informed decisions to manage and reduce the health risks. Studies specifically assessing the PM_2.5, ultrafine particle count and carbon monoxide personal exposure concentrations of adults in an urban transport microenvironment have steadily increased in number over the last decade. However, no recent collective summary is available, particularly one which also considers ultrafine particles; therefore, we present a review of the personal exposure concentration studies for the above named pollutants on different modes of surface transportation (walking, cycling, bus, car and taxi) in the urban transport microenvironment. Comparisons between personal exposure measurements and concentrations recorded at fixed monitoring sites are considered in addition to the factors influencing personal exposure in the transport microenvironment.In general, the exposure studies examined revealed pedestrians and cyclists to experience lower fine particulate matter and CO exposure concentrations in comparison to those inside vehicles—the vehicle shell provided no protection to the passengers. Proximity to the pollutant sources had a significant impact on exposure concentration levels experienced, consequently individuals should be encouraged to use back street routes. Fixed monitoring stations were found to be relatively poor predictors of CO and PM_2.5 exposure concentration levels experienced by individuals in the urban transport microenvironment. Although the mode of transport, traffic and meteorology parameters were commonly identified as significant factors influencing exposure concentrations to the different pollutants under examination, a large amount of the exposure concentration variation in the exposure studies remained unexplained.     

Temporal trends of black carbon concentrations and regional climate forcing in the southeastern United States

The effect of black carbon (BC) on climate forcing is potentially important, but its estimates have large uncertainties due to a lack of sufficient observational data. The BC mass concentration in the southeastern US was measured at a regionally representative site, Mount Gibbes (35.78°N, 82.29°W, 2006 m MSL). The air mass origin was determined using 48-h back trajectories obtained from the hybrid single-particle Lagrangian integrated trajectory model. The highest average concentration is seen in polluted continental air masses and the lowest in marine air masses. During the winter, the overall average BC value was 74.1 ng m⁻³, whereas the overall summer mean BC value is higher by a factor of 3. The main reason for the seasonal difference may be enhanced thermal convection during summer, which increases transport of air pollutants from the planetary boundary layer of the surrounding urban area to this rural site. In the spring of 1998, abnormally high BC concentrations from the continental sector were measured. These concentrations were originating from a biomass burning plume in Mexico. This was confirmed by the observations of the Earth probe total ozone mapping spectrometer. The BC average concentrations of air masses transported from the polluted continental sector during summer are low on Sunday to Tuesday with a minimum value of 256 ng m⁻³ occurring on Monday, and high on Wednesday to Friday with a maximum value of 379 ng m⁻³ occurring on Friday. The net aerosol radiative forcing (scattering effects plus absorption effects) per unit vertical depth at 2006 m MSL is calculated to be −1.38×10⁻³ W m⁻³ for the southeastern US. The magnitude of direct radiative forcing by aerosol scattering is reduced by 15±7% due to the BC absorption.     

High carbon monoxide concentrations during the rainy season in Campo Grande, in central Brazil

This work describes an event of unusually large mixing ratios of carbon monoxide, CO, observed during a typical rainy season time period in central Brazil, when concentrations are expected to be at low levels. CO measurements were performed in Campo Grande (20.02 degrees S; 54.5 degrees W), from July 2001 to October 2002, covering entire periods of the dry and wet seasons. From January to June, average CO was 131 parts per billion by volume (ppbv). During November/December, average CO is about 180 ppbv. On November 13, 521.9 and 565.6 ppbv were observed. It is shown that for this special event, in which there was practically no fire activity at or near the site, air parcels reaching the site were enriched with fire products from regions much further north, near the equatorial region, where the fire activity is delayed in time, compared to central Brazil.     

A study of the relationship of street level carbon monoxide concentrations to traffic parameters

The concentration of carbon monoxide at different locations was measured concurrently with traffic flow and vehicle speeds for a period of 6 months from September 1976 to March 1977. This experiment was carried out in eight streets during different hours of the day. These streets had uniform building density and were all shallow canyons with a height-to-width ratio of about 0.5. Climatic conditions were also recorded.This study was conducted to establish relationships between the CO content of the atmosphere and street and traffic parameters. The measurements were taken at the height of 1.5m from the ground. The CO concentration at the pavement was found, in most cases, to be slightly lower than that at street centerline.The level of carbon monoxide concentration generally decreased as the average vehicle speed increased. In the case of moderate vehicle speeds and high traffic flow, the CO concentration reached values as high as 150 ppm. The variation of CO content of atmosphere with vehicle speed showed a peak indicating that for a certain range of traffic flow, the number of vehicles is more important than the vehicle speed in generating the vehicular pollution.     

fluoride concentrations in the ambient air

The body of the information presented in this paper is of general interest to those concerned with air quality. This paper reports data for ambient atmospheric concentrations of water-soluble fluorides determined in samples of suspended particulate matter collected on glass-fiber filters by the National Air Surveillance Network. Data for over 12,000 samples collected in calendar years 1966, 1967, and 1968 are examined. The purpose of the examination of the data is to give an estimation of current air quality with respect to fluoride content.

The samples are extracted with pure boiling water, and the fluoride concentration of the extracts measured using a fluoride-ion selective electrode. The data engendered are tabulated on an annual basis, and a table is presented summarizing the results. Comparative data will be presented showing the distribution of urban and non-urban stations that exhibit various specified fluoride levels. The results show that the fluoride content in the majority of the samples is below the minimum detectable amount of 0.05 µgF/m³. Conclusions that can be drawn include the observations that: few of the urban samples contain over 1.00 µg/m ³ of fluoride, very few of all samples exceeded 1.00 µ/m³ of fluoride, and no non-urban sample contained over 0.16 µg/m³ of fluoride. It was also concluded that only in rare instances would the fluoride concentrations at the sites sampled be in excess of published standards.