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.     

Relating meteorological variables and trends in motor vehicle emissions to monthly urban carbon monoxide concentrations

A model which quantifies the relationship between the monthly time series for CO emissions, the monthly time series in ambient CO concentration, and meteorologically driven dispersion was developed. Fifteen cities representing a wide range of geographical and climatic conditions were selected. An eight-year time series (1984–1991 inclusive) of monthly averaged data were examined in each city. A new method of handling missing ambient concentration values which is designed to calculate city-wide average concentrations that follow the trend seen at individual monitor sites is presented. This method is general and can be used in other applications involving missing data. The model uses emissions estimates along with two meteorological variables (wind speed and mixing height) to estimate monthly averages of ambient air pollution concentrations. The model is shown to have a wide range of applicability; it works equally well for a wide range of cities that have very different temporal CO distributions. The model is suited for assessing long-term trends in ambient air pollutants and can also be used for estimating seasonal variations in concentration, estimation of trends in emissions, and for filling in gaps in the ambient concentration record.     

Seasonal and long-term trends in atmospheric PAH concentrations: evidence and implications

Atmospheric monitoring data for selected polynuclear aromatic hydrocarbons (PAHs) were compiled from remote, rural and urban locations in the UK, Sweden, Finland and Arctic Canada. The objective was to examine the seasonal and temporal trends, to shed light on the factors which exert a dominant influence over ambient PAH levels. Urban centres in the UK have concentrations 1-2 orders of magnitude higher than in rural Europe and up to 3 orders of magnitude higher than Arctic Canada. Interpretation of the data suggests that proximity to primary sources 'drives' PAH air concentrations. Seasonality, with winter (W) > summer (S), was apparent for most compounds at most sites; high molecular weight compounds (e.g. benzo[a]pyrene) showed this most clearly and consistently. Some low molecular weight compounds (e.g. phenanthrene) sometimes displayed S>W seasonality at some rural locations. Strong W>S seasonality is linked to seasonally-dependent sources which are greater in winter. This implicates inefficient combustion processes, notably the diffusive domestic burning of wood and coal. However, sometimes seasonality can also be strongly influenced by broad changes in meteorology and air mass origin (e.g. in the Canadian Arctic). The datasets examined here suggest a downward trend for many PAHs at some sites, but this is not apparent for all sites and compounds. The inherent noise in ambient air monitoring data makes it difficult to derive unambiguous evidence of underlying declines, to confirm the effectiveness of international source reduction measures.     

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.     

A semi-empirical box modeling approach for predicting the carbon monoxide concentrations at an urban traffic intersection

Emissions generated roadside and at intersections are observed to be affected when there is a sudden change in the traffic flow pattern or increase in the vehicular population, particularly, during peak hours and during special events. The vehicles that queue up at traffic intersections spend a longer amount of time in idle driving mode generating more pollutant emissions per unit time. Other driving patterns (i.e., acceleration, deceleration and cruising) are also observed at intersections, affecting the emission pattern and therefore the resulting pollutant concentrations. The emission rate is not only affected by the increase in the vehicular population but also by the constantly changing traffic flow patterns and vehicles’ driving modes. The nature of the vehicle flows also affects the rate and nature of the dispersion of pollutants in the vicinity of the road, influencing the pollutant concentration. It is, therefore, too complex to simulate the effect of such dynamics on the resulting emission rates using conventional deterministic causal models.In view of this, a simple semi-empirical box model based on the ‘traffic flow rate’, is demonstrated in the present study for estimating the hourly average carbon monoxide (CO) concentrations on a 1-week data at one of the busiest traffic intersections in Delhi. The index of agreement for a whole week, was found to be 0.84, suggesting that the semi-empirical model is 84% error free. A value of 0.87 was found for weekdays and 0.75 for weekend days. The correlation coefficient for the whole week was found to be 0.75, with 0.78 for the weekdays and 0.62 for the weekend days. The RMSE and RRMSE were found to be 1.87% and 41% for a whole week, with 1.81% and 39.93% for the weekdays and 2.0% and 43.47% for the weekend days, respectively. Specific vehicle emission rates are optimized in this study for individual vehicle category, which may be useful in assessing their impacts on the air quality when there is a significant change in a specific vehicular population and the traffic pattern.     

Past and future trends in concentrations of sulphur and nitrogen compounds in the Arctic

Recent trends in nitrogen and sulphur compounds in air and precipitation from a range of Arctic monitoring stations are presented, with seasonal data from the late 70s to 2004 or 2005. Earlier findings of declining sulphur concentrations are confirmed for most stations, while the pattern is less clear for reduced and oxidized nitrogen. In fact there are positive trends for nitrogen compounds in air at several stations. Acidity is generally reduced at many stations while the precipitation amount is either increasing or stable. Variability of sulphate concentrations in air for the period 1991–2000 is reasonably well reproduced at most stations using an Eulerian, hemispherical model. Results for nitrogen compounds are weaker. Scenario studies show that even if large sulphur emission reductions take place in important source regions in South-East Asia in the coming decades, only small changes in Arctic deposition can be expected. This is because South-East Asian emissions have small influence north of the Arctic circle.     

Rural landscape, production and human consumption: past, present and future

Production and consumption of food and in a rural area over the last 400 years were reconstructed for a parish in south east Sweden. This was based on a number of different data sources, including historical maps and official demographic and agricultural statistics. Changes in population (and thus consumption) and the production from arable land and livestock were calculated and used to provide an estimate of the area's supply and demand over time, and of the historical sustainability of the area. Overall food productivity was remarkably constant over time, at approximately 0.04 kgC m(-2) y(-1), despite recent changes in population size and the area of cultivated land. The empirical results from the past and the present, together with the future land changes due to shoreline displacement were used to predict the situation in the future. These final estimates can be used in the assessment of risk for exposure to contaminated food for the future population in the area.     

China's natural wetlands: past problems, current status, and future challenges

Natural wetlands, occupying 3.8% of China's land and providing 54.9% of ecosystem services, are unevenly distributed among eight wetland regions. Natural wetlands in China suffered great loss and degradation (e.g., 23.0% freshwater swamps, 51.2% costal wetlands) because of the wetland reclamation during China's long history of civilization, and the population pressure and the misguided policies over the last 50 years. Recently, with an improved understanding that healthy wetland ecosystems play a vital role in her sustainable economic development, China started major efforts in wetland conservation, as signified by the policy to return reclaimed croplands to wetlands, the funding of billions of dollars to restore degraded wetlands, and the national plan to place 90% of natural wetlands under protection by 2030. This paper describes the current status of the natural wetlands in China, reviews past problems, and discusses current efforts and future challenges in protecting China's natural wetlands.     

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.     

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.     

Role of multidrug resistance-associated proteins in cancer therapeutics: past,present, and future perspectives

Environmental Science and Pollution Research - Cancer, a major public health problem, is one of the world’s top leading causes of death. Common treatments for cancer include cytotoxic...     

Increasing concentrations of CO and O3 rising deforestation rates and increasing troposheric carbon monoxide and ozone in Amazonia

Increasing carbon monoxide and ozone concentrations have been observed in the lower troposphere of the Brazilian Amazon region in recent years (1989–1995). Carbon monoxide and ozone have been measured in the region continuously; from observations at a single site and many sporadic field missions, there is a clear indication that the chemical activity in the troposphere is growing, with increasing concentrations especially during the dry season. On the other hand, the most recent deforestation assessment by the Brazilian Government, performed by the Instituto Nacional de Pesquisas Espaciais (INPE) using Landsat data, shows yearly rates rising from the 11,130 km² year^?1 minimum of the 1990/91 survey, to 13,786 km² year^?1 for the 1991/92 period, and 14,896 km² year^?1 for the period 1992/94. It is argued that the increase in deforestation/biomass burning activities in “Amazonia” have produced larger carbon monoxide and ozone concentrations in the lower atmosphere.     

Evaluation of an intensive sampling and analysis method for carbon monoxide

This paper describes a portable, low-cost whole air sampler capable of collecting 12 1-L samples in tedlar bags and using a single "D" cell for power. The results are presented from two tests of an intensive sampling and analysis method for measuring ambient carbon monoxide (CO) concentrations in urban areas using this sampler. The method is evaluated in comparison with an approved continuous CO analyzer, in intercomparisons of the results of re-analysis of the samples, and by examination of the results from co-located samplers. The precision of the analytical method was found to be +/-0.30 ppmv. The precision of the sampling method was found to be +/-0.73 ppmv and therefore is the limiting factor in the method's overall precision. These values are sufficient to verify attainment of National Ambient Air Quality Standards (NAAQS) levels in urban areas. Improvements in the sampler and analytical procedure are discussed.     

Atmospheric PCBs and organochlorine pesticides in Birmingham,UK: concentrations,sources, temporal and seasonal trends

Concentrations of individual PCBs and DDT, DDE, α- and γ-HCH were recorded in 62 air samples of 24 h duration taken every 1–2 weeks at an urban location in Birmingham, UK between April 1999 and July 2000. Concentrations of PCBs 31/28, 52, 49, 47, 105, 149, 153, 138/164, 174, and 180 were significantly lower (p<0.05) than those recorded at the same site in 1997–1998. While DDT concentrations and DDT:DDE ratios were much lower than those recorded in southern England in 1992–1993; no such decline was observed in concentrations of α- and γ-HCH, or the α:γ-HCH ratio. These data are consistent with declining European usage of DDT, but continuing UK use of γ-HCH, and overseas use and subsequent atmospheric transport of “technical” HCH. γ-HCH concentrations displayed two non-temperature dependent peaks in spring and late summer/early autumn, consistent with agricultural use patterns. Multiple linear regression analysis was used to elucidate the relative influence of temperature, wind direction and a variety of other meteorological variables on atmospheric concentrations of PCBs. When all samples were considered, concentrations of most PCB congeners were influenced by a combination of reciprocal temperature, wind direction, and wind speed. Plotting the ratio of the Beta weightings for the regression coefficients for reciprocal temperature and sine (or cosine) of wind direction against chlorine number, revealed a general increase in the relative influence of temperature compared to wind direction with increasing chlorine number. However, when the 31 samples for which the wind speed <4.4 m s⁻¹ were analysed; only temperature and atmospheric relative humidity were influential for most congeners. This absence of influence of wind direction under relatively calm atmospheric conditions, suggests that it is medium-to-long range transport rather than local sources that exerts the greatest influence on PCB concentrations at our site.     

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 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.     

Concentrations of volatile organic compounds,carbon monoxide,carbon dioxide and particulate matter in buses on highways in Taiwan

Although airborne pollutants in urban buses have been studied in many cities globally, long-distance buses running mainly on highways have not been addressed in this regard. This study investigates the levels of volatile organic compounds (VOCs), carbon monoxide (CO), carbon dioxide (CO₂) and particulate matter (PM) in the long-distance buses in Taiwan. Analytical results indicate that pollutants levels in long-distance buses are generally lower than those in urban buses. This finding is attributable to the driving speed and patterns of long-distance buses, as well as the meteorological and geographical features of the highway surroundings. The levels of benzene, toluene, ethylbenzene and xylene (BTEX) found in bus cabins exceed the proposed indoor VOC guidelines for aromatic compounds, and are likely attributable to the interior trim in the cabins. The overall average CO level is 2.3 ppm, with higher average level on local streets (2.9 ppm) than on highways (2.2 ppm). The average CO₂ level is 1493 ppm, which is higher than the guideline for non-industrial occupied settings. The average PM level in this study is lower than those in urban buses and IAQ guidelines set by Taiwan EPA. However, the average PM₁₀ and PM_2.5 is higher than the level set by WHO. Besides the probable causes mentioned above, fewer passenger movements and less particle re-suspension from bus floor might also cause the lower PM levels. Measurements of particle size distribution reveal that more than 75% of particles are in submicron and smaller sizes. These particles may come from the infiltration from the outdoor air. This study concludes that air exchange rates in long-distance buses should be increased in order to reduce CO₂ levels. Future research on long-distance buses should focus on the emission of VOCs from brand new buses, and the sources of submicron particles in bus cabins.     

Effects of biodiesel made from swine and chicken fat residues on carbon monoxide,carbon dioxide,and nitrogen oxide emissions

The effects of two alternative sources of animal fat-derived biodiesel feedstock on CO₂, CO, NO_x tailpipe emissions as well as fuel consumption were investigated. Biodiesel blends were produced from chicken and swine fat waste (FW-1) or floating fat (FW-2) collected from slaughterhouse wastewater treatment processes. Tests were conducted in an unmodified stationary diesel engine operating under idling conditions in attempt to simulate slow traffic in urban areas. Significant reductions in CO (up to 47% for B100; FW-2) and NO_x (up to 20% for B5; FW-2 or B100; FW-1) were attained when using biodiesel fuels at the expense of 5% increase in fuel consumption. Principal component analysis (PCA) was performed to elucidate possible associations among gas (CO₂, CO, and NO_x) emissions, cetane number and iodine index with different sources of feedstock typically employed in the biodiesel industry. NO_x, cetane number and iodine index were inversely proportional to CO₂ and biodiesel concentration. High NO_x emissions were reported from high iodine index biodiesel derived especially from forestry, fishery and some agriculture feedstocks, while the biodiesel derived from animal sources consistently presented lower iodine index mitigating NO_x emissions. The obtained results point out the applicability of biodiesel fuels derived from fat-rich residues originated from animal production on mitigation of greenhouse gas emissions. The information may encourage practitioners from biodiesel industry whilst contributing towards development of sustainable animal production.

Implications: Emissions from motor vehicles can contribute considerably to the levels of greenhouse gases in the atmosphere. The use of biodiesel to replace or augment diesel can not only decrease our dependency on fossil fuels but also help decrease air pollution. Thus, different sources of feedstocks are constantly being explored for affordable biodiesel production. However, the amount of carbon monoxide (CO), carbon dioxide (CO₂), and/or nitrogen oxide (NO_x) emissions can vary largely depending on type of feedstock used to produce biodiesel. In this work, the authors demonstrated animal fat feasibility in replacing petrodiesel with less impact regarding greenhouse gas emissions than other sources.     

Spatial inhomogeneity in pollutant concentrations, and their implications for air quality model evaluation

The Southern California Air Quality Study database provides a valuable resource with which to test urban-scale photochemical models and to achieve a better understanding of the atmospheric dynamics of pollutant formation. The CIT model was evaluated using the SCAQS database according to traditional model performance guidelines. A first application, reported previously, focused on model enhancement and application of the model to the 27–29 August 1987 episode. This study evaluates the CIT model using the 24–25 June SCAQS episode, providing further evaluation of the model. Results show that the CIT airshed model can follow the diurnal variations of reactive species and the transport for relatively unreactive species. The normalized gross error for ozone was 31 % in June compared to 38% in August. However, to fully judge model performance in proper perspective, a question arises: “How well do the measurements reflect the air quality surrounding the monitoring station, not just in that location?” This is an important but seldom quantitatively considered factor, not only in model evaluation but in the study of health effects as well. Analyses indicate that individual concentration measurements only approximately represent the true volume-averaged concentrations within a computational grid cell and that significant spatial variations exist. Thus any evaluation of models using these data sets should take these local variations into consideration. A series of tests found that the local inhomogeneities had a normalized gross error in the range of 25–45% depending on the pollutant. In this context, the performance of the CIT model is consistent with known modeling limitations such as emissions inventories and sub-grid scale variation of observations.