Daily Mortality in the Philadelphia Metropolitan Area and Size-Classified Particulate Matter

ABSTRACT

Time-series of daily mortality data from May 1992 to September 1995 for various portions of the seven-county Philadelphia, PA, metropolitan area were analyzed in relation to weather and a variety of ambient air quality parameters. The air quality data included measurements of size-classified PM, SO₄ ^2-, and H+ that had been collected by the Harvard School of Public Health, as well as routine air pollution monitoring data. Because the various pollutants of interest were measured at different locations within the metropolitan area, it was necessary to test for spatial sensitivity by comparing results for different combinations of locations. Estimates are presented for single pollutants and for multiple-pollutant models, including gaseous pollutants and mutually exclusive components of PM (PM_2.5 and coarse particles, SO₄ ^2- and non-SO₄ ^2- portions of total suspended particulate [TSP] and PM₁₀), measured on the day of death and the previous day.

We concluded that associations between air quality and mortality were not limited to data collected in the same part of the metropolitan area; that is, mortality for one part may be associated with air quality data from another, not necessarily neighboring, part. Significant associations were found for a wide variety of gaseous and particulate pollutants, especially for peak O₃. Using joint regressions on peak O₃ with various other pollutants, we found that the combined responses were insensitive to the specific other pollutant selected. We saw no systematic differences according to particle size or chemistry. In general, the associations between daily mortality and air pollution depended on the pollutant or the PM metric, the type of collection filter used, and the location of sampling. Although peak O₃ seemed to exhibit the most consistent mortality responses, this finding should be confirmed by analyzing separate seasons and other time periods.     

Effect of the Fine Fraction of Particulate Matter versus the Coarse Mass and Other Pollutants on Daily Mortality in Santiago,Chile

ABSTRACT

Daily counts of non-accidental deaths in Santiago, Chile, from 1988 to 1996 were regressed on six air pollutants— fine particles (PM_2.5), coarse particles (PM_10–2.5), CO, SO₂, NO₂, and O₃. Controlling for seasonal and meteorological conditions was done using three different models— a generalized linear model, a generalized additive model, and a generalized additive model on previously filtered data. Single- and two-pollutant models were tested for lags of 1-5 days and the average of the previous 2-5 days.

The increase in mortality associated with the mean levels of air pollution varied from 4 to 11%, depending on the pollutants and the way season of the year was considered. The results were not sensitive to the modeling approaches, but different effects for warmer and colder months were found. Fine particles were more important than coarse particles in the whole year and in winter, but not in summer. NO₂ and CO were also significantly associated with daily mortality, as was O₃ in the warmer months. No consistent effect was observed for SO₂. Given particle composition in Santiago, these results suggest that combustion-generated pollutants, especially from motor vehicles, may be associated with increased mortality. Temperature was closely associated with mortality. High temperatures led to deaths on the same day, while low temperatures lead to deaths from 1 to 4 days later.     

The Impact of a Building Implosion on Airborne Particulate Matter in an Urban Community

Abstract

In response to community concerns, the air quality impact of imploding a 22-story building in east Baltimore, MD, was studied. Time- and space-resolved concentrations of indoor and outdoor particulate matter (PM) (nominally 0.5–10 µm) were measured using a portable nephelometer at seven and four locations, respectively. PM₁₀ levels varied in time and space; there was no measurable effect observed upwind of the implosion. The downwind peak PM₁₀ levels varied with distance (54,000–589 µg/m³) exceeding pre-implosion levels for sites 100 and 1130 m 3000- and 20-fold, respectively. Estimated outdoor 24-hr integrated mass concentrations varied from 15 to 72 µg/m³. The implosion did not result in the U.S. Environmental Protection Agency (EPA) National Ambient Air Quality Standard (NAAQS) for PM₁₀ being exceeded. X-ray fluorescence analysis indicated that the elemental composition was dominated by crustal elements: calcium (57%), silicon (23%), aluminum (7.6%), and iron (6.1%). Lead was above background but at a low level (0.17 µg/m³). Peak PM₁₀ concentrations were short-lived; most sites returned to background within 15 min. No increase in indoor PM₁₀ was observed even at the most proximate 250 m location. These results demonstrate that a building implosion can have a severe but short-lived impact on community air quality. Effective protection is offered by being indoors or upwind.     

Atmospheric Particulate Matter and Polycyclic Aromatic Hydrocarbons for PM10 and Size-Segregated Samples in Bangkok

Abstract

Air samples of particulate matter (PM) with an aerodynamic diameter less than 10 µm (PM₁₀) were collected from six sites in Bangkok, Thailand, using high-volume air samplers. Daily samples were taken at intervals of 12 days from November 1999 to November 2000. Size-selected sampling using a multislit Andersen size-fractionated cascade impactor was undertaken at one site in central Bangkok to identify particulate size distribution. The annual average PM₁₀ concentration at all six sites exceeded the Thailand National Ambient Air Quality Standard (NAAQS) of 50 µg/m³. The daily PM₁₀ concentrations at heavy traffic roadside areas ranged between 30 and 160 µg/m³. The highest PM₁₀ level occurred during the winter period (November–February), which is the dry season. From our results, which are based on a 1-yr survey, it can be observed that the particulate concentrations are associated with traffic volumes and seasonal factors (temperature and rainfall). The relative importance of size fractions in contributing to PM load is presented and discussed. Twenty polycyclic aromatic hydro-carbons (PAHs) associated with PM have been identified and quantified. The summed PAHs based on the 20 species had an average concentration of 60 ng/m³. Benzo(e)pyrene, indeno(123cd)pyrene, and benzo(ghi)perylene were the major compounds with average concentrations of 8, 10, and 13 ng/m³, respectively. Results indicate that more than 97% of PAHs were found in the small particulate size range of <0.95 µm.     

Roadside Particulate Air Pollution in Bangkok

Abstract

Airborne fine particles of PM_2.5-10 and PM_2.5 in Bangkok, Nonthaburi, and Ayutthaya were measured from December 22, 1998, to March 26, 1999, and from November 30, 1999, to December 2, 1999. Almost all the PM₁₀ values in the high-polluted (H) area exceeded the Thailand National Ambient Air Quality Standards (NAAQS) of 120 μg/m³. The low-polluted (L) area showed low PM₁₀ (34–74 μg/m³ in the daytime and 54–89 μg/m³ at night). PM_2.5 in the H area varied between 82 and 143 μg/m³ in the daytime and between 45 and 146 μg/m³ at night. In the L area, PM_2.5 was quite low both day and night and varied between 24 and 54 μg/m³, lower than the U.S. Environmental Protection Agency (EPA) standard (65 μg/m³). The personal exposure results showed a significantly higher proportion of PM_2.5 to PM₁₀ in the H area than in the L area (H = 0.80 ± 0.08 and L = 0.65 ± 0.04).

Roadside PM₁₀ was measured simultaneously with the Thailand Pollution Control Department (PCD) monitoring station at the same site and at the intersections where police work. The result from dual simultaneous measurements of PM₁₀ showed a good correlation (correlation coefficient: r = 0.93); however, PM levels near the roadside at the intersections were higher than the concentrations at the monitoring station. The relationship between ambient PM level and actual personal exposures was examined. Correlation coefficients between the general ambient outdoors and personal exposure levels were 0.92 for both PM_2.5 and PM₁₀.

Bangkok air quality data for 1997–2000, including 24-hr average PM₁₀, NO₂, SO₂, and O₃ from eight PCD monitoring stations, were analyzed and validated. The annual arithmetic mean PM₁₀ of the PCD data at the roadside monitoring stations for the last 3 years decreased from 130 to 73 μg/m³, whereas the corresponding levels at the general monitoring stations decreased from 90 to 49 μg/m³. The proportion of days when the level of the 24-hr average PM₁₀ exceeded the NAAQS was between 13 and 26% at roadside stations. PCD data showed PM₁₀ was well correlated with NO₂ but not with SO₂, suggesting that automobile exhaust is the main source of the particulate air pollution. The results obtained from the simultaneous measurement of PM_2.5 and PM₁₀ indicate the potential environmental health hazard of fine particles. In conclusion, Bangkok traffic police were exposed to high levels of automobile-derived particulate air pollution.     

In-vehicle carbon dioxide concentration in commuting cars in Bangkok,Thailand

It is known that in-vehicle carbon dioxide (CO₂) concentration tends to increase due to occupant exhalation when the HVAC (heating, ventilation, and air conditioning) air is in recirculation mode. Field experiments were conducted to measure CO₂ concentration during typical commute in Bangkok, Thailand. The measured concentrations agreed with the concentration predicted using first-order mass balance equation, in both recirculating and outside air modes. The long-term transient decay of the concentration when the vehicle was parked and the HVAC system was turned off was also studied. This decay was found to follow Fickian diffusion process. The paper also provides useful operational details of the automotive HVAC system and fresh air ventilation exchange between cabin interior and exterior.

Implications: Drivers in tropical Asian countries typically use HVAC recirculation mode in their automobiles. This behavior leads to excessive buildup of cabin CO₂ concentration levels. The paper describes the CO₂ buildup in a typical commute in Bangkok, Thailand. Auto manufacturers can potentially take measures to alleviate such high concentration levels. The paper also discusses the diffusion of CO₂ through the vehicle envelope, an area that has never been investigated before.     

Characterization of Particulate Matter in California

ABSTRACT

The size, composition, and concentration of particulate matter (PM) vary with location and time. Several monitoring/sampling programs are operated in California to characterize PM less than 2.5 and 10 µm in aerodynamic diameter (PM_2.5 and PM₁₀). This paper presents a broad summary of the spatial and temporal variations observed in ambient PM_2.5 and PM₁₀ concentrations in California. Many areas that have high PM₁₀ concentrations also have relatively high PM_2.5 concentrations, and data indicate that a significant portion of the PM₁₀ air quality problem is caused by PM_2.5. To develop effective plans for attaining the ambient PM standards, improved understanding of these unique problems is needed. Since 1989, pollution control efforts—whether specifically targeted for particulate matter or indirectly via controls on gaseous emissions—have caused annual average PM_2.5 and PM₁₀ concentrations to decline at most sites in California.     

Organochlorine pesticide and polychlorinated biphenyl residues in foodstuffs from Bangkok, Thailand

Raw foodstuffs collected from Bangkok, Thailand, were analysed for the presence of PCBs, DDTs, HCHs (BHCs). HCB, aldrin, dieldrin, heptachlor and heptachlor epoxide. Residues of PCBs and organochlorine pesticides were detected in all the samples analysed. Concentrations of PCBs did not reach the tolerance limit set forth by the US Food and Drug Administration (FDA). The concentrations of SigmaHCH were higher than those of SigmaDDT in all the farm products while the levels of SigmaDDT were greater in fishes including fish flakes and fishmeal. Meat samples recorded higher concentrations of SigmaDDT and dieldrin than SigmaHCH. Comparing the levels of organochlorines in foodstuffs from Bangkok, considerable levels of aldrin and dieldrin indicate the need for concern from the food safety point of view because of their much higher toxicity than DDT and other organochlorines. However, the levels did not exceed the Maximum Residue Limit (MRL) recommended by FAO/WHO. Food contamination by HCB, heptachlor and heptachlor epoxide is comparatively lower.     

Effects of 10% biofuel substitution on ground level ozone formation in Bangkok,Thailand

The Thai Government's search for alternatives to imported petroleum led to the consideration of mandating 10% biofuel blends (biodiesel and gasohol) by 2012. Concerns over the effects of biofuel combustion on ground level ozone formation in relation to their conventional counterparts need addressing. Ozone formation in Bangkok is explored using a trajectory box model. The model is compared against O₃, NO, and NO₂ time concentration data from air monitoring stations operated by the Thai Pollution Control Department. Four high ozone days in 2006 were selected for modeling. Both the traditional trajectory approach and a citywide average approach were used. The model performs well with both approaches but slightly better with the citywide average. Highly uncertain and missing data are derived within realistic bounds using a genetic algorithm optimization. It was found that 10% biofuel substitution will lead to as much as a 16 ppb peak O₃ increase on these four days compared to a 48 ppb increase due to the predicted vehicle fleet size increase between 2006 and 2012. The approach also suggests that when detailed meteorological data is not available to run three dimensional airshed models, and if the air is stagnant or predominately remains over an urban area during the day, that a simple low cost trajectory analysis of O₃ formation may be applicable.     

Sources of Atmospheric Carbonaceous Particulate Matter in Pittsburgh,Pennsylvania

Abstract

The organic carbon (OC)/elemental carbon (EC) tracer method is applied to the Pittsburgh, PA, area to estimate the contribution of secondary organic aerosol (SOA) to the monthly average concentration of organic particu-late matter (PM) during 1995. An emissions inventory is constructed for the primary emissions of OC and EC in the area of interest. The ratio of primary emissions of OC to those of EC ranges between 2.4 in the winter months and 1.0 in the summer months. A mass balance model and ambient measurements were used to assess the accuracy of the emissions inventory. It is estimated to be accurate to within 50%. The results from this analysis show a strong monthly dependence on SOA contribution to the total organic PM concentration, varying from near zero during winter months to 50% or more of the total OC concentration in the summer.     

A Pilot Indoor-Outdoor Study of Organic Particulate Matter and Particulate Mutagenicity

Abstract

Many large metropolitan areas experience elevated concentrations of ground-level ozone pollution during the summertime “smog season”. Local environmental or health agencies often need to make daily air pollution forecasts for public advisories and for input into decisions regarding abatement measures and air quality management. Such forecasts are usually based on statistical relationships between weather conditions and ambient air pollution concentrations. Multivariate linear regression models have been widely used for this purpose, and well-specified regressions can provide reasonable results. However, pollution-weather relationships are typically complex and nonlinear—especially for ozone—properties that might be better captured by neural networks. This study investigates the potential for using neural networks to forecast ozone pollution, as compared to traditional regression models. Multiple regression models and neural networks are examined for a range of cities under different climate and ozone regimes, enabling a comparative study of the two approaches. Model comparison statistics indicate that neural network techniques are somewhat (but not dramatically) better than regression models for daily ozone prediction, and that all types of models are sensitive to different weather-ozone regimes and the role of persistence in aiding predictions.     

Determination of Levoglucosan in Atmospheric Fine Particulate Matter

Abstract

A microanalytical method suitable for the quantitative determination of the sugar anhydride levoglucosan in low-volume samples of atmospheric fine particulate matter (PM) has been developed and validated. The method incorporates two sugar anhydrides as quality control standards. The recovery standard sedoheptulosan (2,7-anhydro-β-D-altro-heptulopyranose) in 20 μL solvent is added onto samples of the atmospheric fine PM and aged for 1 hr before ultrasonic extraction with ethylacetate/ triethylamine. The extract is reduced in volume, an internal standard is added (1,5-anhydro-D-mannitol), and a portion of the extract is derivatized with 10% by volume N-trimethylsilylimidazole. The derivatized extract is analyzed by gas chromatography/mass spectrometry (GC/MS). The recovery of levoglucosan using this procedure was 69 ± 6% from five filters amended with 2 μg levoglu-cosan, and the reproducibility of the assay is 9%. The limit of detection is ～0.1 μg/mL, which is equivalent to ～3.5 ng/m³ for a 10 L/min sampler or ～8.7 ng/m³ for a 4 L/min personal sampler (assuming 24-hr integrated samples). We demonstrated that levoglucosan concentrations in collocated samples (expressed as ng/m³) were identical irrespective of whether samples were collected by PM with aerodynamic diameter ≤2.5 μm or PM with aerodynamic diameter ≤10 μm impactors. It was also demonstrated that X-ray fluorescence analysis of samples of atmospheric PM, before levoglucosan determinations, did not alter the levels of levoglucosan.     

The Association between Ambient Carbon Monoxide Levels and Daily Mortality in Toronto,Canada

ABSTRACT

The role of ambient levels of carbon monoxide (CO) in the exacerbation of heart problems in individuals with both cardiac and other diseases was examined by comparing daily variations in CO levels and daily fluctuations in nonaccidental mortality in metropolitan Toronto for the 15-year period 1980–1994. After adjusting the mortality time series for day-of-the-week effects, nonparametic smoothed functions of day of study and weather variables, statistically significant positive associations were observed between daily fluctuations in mortality and ambient levels of carbon monoxide, nitrogen dioxide, sulfur dioxide, coefficient of haze, total suspended particulate matter, sulfates, and estimated PM_2.5 and PM₁₀. However, the effects of this complex mixture of air pollutants could be almost completely explained by the levels of CO and total suspended particulates (TSP). Of the 40 daily nonaccidental deaths in metropolitan Toronto, 4.7% (95% confidence interval of 3.4%–6.1%) could be attributable to CO while TSP contributed an additional 1.0% (95% confidence interval of 0.2–1.9%), based on changes in CO and TSP equivalent to their average concentrations. Statistically significant positive associations were observed between CO and mortality in all seasons, age, and disease groupings examined. Carbon monoxide should be considered as a potential public health risk to urban populations at current ambient exposure levels.     

Impact of Toll Removal on Air Particulate Concentration in Jacksonville,Florida

The concentration of total suspended particulate (TSP) matter was determined at commercial, residential, rural and industrial sites in metropolitan Jacksonville during the summers of 1989 and 1990. These data were compared to samples taken at the Mathews Bridge Toll Plaza in 1989 and at a similar location one year later, after removal of the toll facility. All samples were analyzed by reflectance analysis and the approximate elemental carbon content used to estimate the contribution of vehicular traffic at the roadway. The results indicate a significant improvement in air quality at the location of the previous toll facility, but did not show that a widespread improvement resulted from the removal of tolls in Jacksonville, Florida.     

Toxicologic Appraisal of Particulate Matter,Oxides of Sulfur,and Sulfuric Acid

An examination of the available toxicological literature indicates that sulfur dioxide itself would be properly classified as a mild respiratory irritant, the main portion of which is absorbed in the upper respiratory tract. The reported industrial experience of symptoms of mild chronic respiratory irritation from exposures at or above 5 ppm is compatible with what would have been predicted on the basis of available toxicological data. The basic physiological response to inhalation of pure SO₂ appears to be a mild degree of bronchoconstriction reflected in a measurable increase in flow resistance. Although the response is highly variable, most individuals tested have responded to 5 ppm and levels of 5 to 10 ppm have upon occasion produced severe bronchospasm in sensitive individuals. This serves to point up the fact that experience with the industrial Threshold Limit Value (5 ppm) is not applicable as a guide for the general population. Although the majority of individuals tested have shown no detectable response to levels of 1 ppm, there are again sensitive individuals who have responded. It is not known whether these individuals would have responded to concentrations lower than this. The response of these more sensitive individuals to 1 ppm would be classified as detectable response, not as severe bronchospasm. An examination of the available toxicological literature also indicates that sulfuric acid and irritant sulfates, to the extent that the latter have been examined, are more potent irritants than sulfur dioxide. This has been demonstrated in studies using morality and lung pathology as criteria as well as in studies using alterations in pulmonary function in experimental animals and human subjects. The irritant potency of these substances is affected by particle size and by relative humidity, which factors are probably interrelated. It is unfortunate that these substances have not been as yet studied in as great detail as has the less irritant sulfur dioxide. There is evidence which cannot be ignored, even though it is based entirely on animal experiments of one investigator, indicating that the presence of particulate material capable of oxidizing sulfur dioxide to sulfuric acid caused a three to fourfold potentiation of the irritant response. The aerosols causing this potentiation were soluble salts of ferrous iron, manganese and vanadium all of which would become droplets upon inhalation. Insoluble aerosols such as carbon, iron oxide fume, triphenylphosphate or fly ash did not cause a potentiation of the irritant action of SO₂ even when used at higher concentrations. The concentrations of SO₂ used in these various experiments were in some cases as low as 0.16 ppm. The catalytic aerosols were used at concentrations of 0.7 to 1 mg/m³ which is above any reported levels of these metals in urban air. If the SO₂ present as an air pollutant remained unaltered until removed by dilution, there would be no evidence in the toxicological literature suggesting that it would be likely to have any effects on man at prevailing levels. Studies of atmospheric chemistry have shown that SO₂ does not remain unaltered in the atmosphere, especially under onditions of high humidity and in the presence of particulate material, but is converted to H₂SO₄. Such a conversion increases its irritant potency. On this basis the toxicological literature combined with the literature of atmospheric chemistry suggest that sulfur dioxide levels be controlled in terms of the potential formation of irritant particles. This means that control measures as far as feasible should be aimed at both SO₂ and particulate material and not against either alone.     

Performance of Wet Scrubbers on Liquid and Solid Particulate Matter

A general discussion of packed scrubbers for particle collection is presented. Data on liquid entrainment separation, ammonium chloride fume collection, and clay particle collection are given.     

Characterization of Particulate Matter for Three Sites in Kuwait

Abstract

Many studies have shown strong associations between particulate matter (PM) levels and a variety of health outcomes, leading to changes in air quality standards in many regions, especially the United States and Europe. Kuwait, a desert country located on the Persian Gulf, has a large petroleum industry with associated industrial and urban land uses. It was marked by environmental destruction from the 1990 Iraqi invasion and subsequent oil fires. A detailed particle characterization study was conducted over 12 months in 2004–2005 at three sites simultaneously with an additional 6 months at one of the sites. Two sites were in urban areas (central and southern) and one in a remote desert location (northern). This paper reports the concentrations of particles less than 10 µm in diameter (PM₁₀) and fine PM (PM_2.5), as well as fine particle nitrate, sulfate, elemental carbon (EC), organic carbon (OC), and elements measured at the three sites. Mean annual concentrations for PM₁₀ ranged from 66 to 93 µg/m³ across the three sites, exceeding the World Health Organization (WHO) air quality guidelines for PM₁₀ of 20 µg/m³. The arithmetic mean PM_2.5 concentrations varied from 38 and 37 µg/m³ at the central and southern sites, respectively, to 31 µg/m³ at the northern site. All sites had mean PM_2.5 concentrations more than double the U.S. National Ambient Air Quality Standard (NAAQS) for PM_2.5. Coarse particles comprised 50–60% of PM₁₀. The high levels of PM₁₀ and large fraction of coarse particles comprising PM₁₀ are partially explained by the resuspension of dust and soil from the desert crust. However, EC, OC, and most of the elements were significantly higher at the urbanized sites, compared with the more remote northern site, indicating significant pollutant contributions from local mobile and stationary sources. The particulate levels in this study are high enough to generate substantial health impacts and present opportunities for improving public health by reducing airborne PM.     

Oxalic Acid in PM2.5 Particulate Matter in California

ABSTRACT

Ambient air monitoring for organic acids in PM₂₅ was conducted at several locations in California. During the study, it was found that oxalic acid (ethanedioc acid) was the most abundant organic acid found in the PM_{2 5} fraction. Samples from Azuza (in southern California), San Jose (in the San Francisco Bay area), and Fresno (in central California), a PM_2.5 Super Site, were collected in 1999 and analyzed. The results for oxalic acid concentrations during this monitoring effort are presented.     

Considering the effects of ambient particulate matter on the lung function of motorcycle taxi drivers in Bangkok,Thailand

The motorcycle taxi drivers of Bangkok have been heavily exposed to high concentrations of PM₁₀ (particulate matter with an aerodynamic diameter ≤10 μm), and the impact of this on their lungs has been neither documented nor studied. This study examines the association between exposure to PM₁₀ and lung function decline among motorcycle taxi drivers. A cross-sectional study was conducted in Bangkok between two groups: a subject group of motorcycle taxi drivers and control group of enclosed vehicle taxi drivers. The findings of the Thailand Pollution Control Department were used to estimate the annual ambient PM₁₀ concentration levels in the metropolis. Pulmonary functions of motorcycle taxi drivers and enclosed vehicle taxi drivers were measured and compared using the Mann-Whitney test. Multiple linear regression analysis was applied to estimate the effects of PM₁₀ exposure on the lung function of motorcycle taxi drivers. A total of 1283 motorcycle taxi drivers and 600 taxi drivers were investigated. The mean forced expiratory volume in 1 sec/forced vital capacity (FEV₁/FVC) of the motorcycle taxi drivers was significantly lower than that of the taxi drivers (P < 0.001). The mean FEV₁/FVC of motorcycle taxi drivers exposed to ≥50 µg/m³ PM₁₀ was statistically lower (?2.82%; 95% confidence interval [CI]: ?4.54% to ?1.09%) and the mean % vital capacity (%VC) of those exposed to 40–49.9 µg/m³ PM₁₀ was statistically lower than that of motorcycle taxi drivers exposed to <30 µg/m³ PM₁₀ (?3.33%; 95% CI: ?5.79% to ?0.87%). Motorcycle taxi drivers were directly exposed to air pollution in their working environment. As a result, their lung function might decrease more than that of enclosed vehicle taxi drivers. With the possible exposure to ≥50 µg/m³ PM₁₀, the vehicular emission standards should be vigorously enforced. Further investigation is warranted to clarify the effect of lung dysfunction on the work and lifestyle of motorcycle taxi drivers.

Implications: Motorcycle taxi drivers are directly exposed to air pollution in their work environment; therefore, their lung function might decrease more than that of enclosed vehicle taxi drivers, especially when exposed to ≥50 µg/m³ PM₁₀. World Health Organization (WHO) vehicular emission standards should be recognized and eventually enforced.