Threshold Dependence of Mortality Effects for Fine and Coarse Particles in Phoenix,Arizona

ABSTRACT

Daily data for fine (<2.5 um) and coarse (2.5-10 um) particles are available for 1995-1997 from the U.S. Environmental Protection Agency (EPA) research monitor in Phoenix, AZ. Mortality effects on the 65 and over population were studied for both the city of Phoenix and for a region of about 50 mi around Phoenix. Coarse particles in Phoenix are believed to be natural in origin and spatially homogeneous, whereas fine particles are primarily vehicular in origin and concentrated in the city itself. For this reason, it is natural to focus on city mortality data when considering fine particles, and on region mortality data when considering coarse particles, and most of the results reported here correspond to those assignments.

After allowing for seasonality and long-term trend through a nonlinear (B-spline) trend curve, and also for meteorological effects based on temperature and specific humidity, a regression of mortality was performed on PM using several different measures for PM. Based on a linear PM effect, we found a statistically significant coefficient for coarse particles, but not for fine particles, contrary to what is widely believed about the effects of coarse and fine particles. An analysis of nonlinear pollution-mortality relationships, however, suggests that the true picture is more complicated than that. For coarse particles, the evidence for any nonlinear or threshold-based effect is slight. For fine particles, we found evidence of a threshold, most likely with values in the range of 20-25 ug/m³. We also found some evidence of interactions of the PM effects with season and year.

The main effect here is an apparent seasonal interaction in the coarse PM effect. An attempt was made to explain this in terms of seasonal variation in the chemical composition of PM, but this led to another counterintuitive result: the PM effect is highest in spring and summer, when the anthropogenic concentration of coarse PM is lowest as determined by a principal components analysis. There was no evidence of confounding between the fine and coarse PM effects. Although these results are based on one city and should be considered tentative until replicated in other studies, they suggest that the prevailing focus on fine rather than coarse particles may be an oversimplification. The study also shows that consideration of nonlinear effects can lead to real changes of interpretation and raises the possibility of seasonal effects associated with the chemical composition of PM.     

Effect of the fine fraction of particulate matter versus the coarse mass and other pollutants on daily mortality in Santiago, Chile

Daily counts of non-accidental deaths in Santiago, Chile, from 1988 to 1996 were regressed on six air pollutants--fine particles (PM2.5), coarse particles (PM10-2.5), 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.     

A study of the association between daily mortality and ambient air pollutant concentrations in Pittsburgh, Pennsylvania

We have studied the possible association of daily mortality with ambient pollutant concentrations (PM10, CO, O3, SO2, NO2, and fine [PM2.5] and coarse PM) and weather variables (temperature and dew point) in the Pittsburgh, PA, area for two age groups--less than 75, and 75 and over--for the 3-year period of 1989-1991. Correlation functions among pollutant concentrations show important seasonal dependence, and this fact necessitates the use of seasonal models to better identify the link between ambient pollutant concentrations and daily mortality. An analysis of the seasonal model results for the younger-age group reveals significant multicollinearity problems among the highly correlated concentrations of PM10, CO, and NO2 (and O3 in spring and summer), and calls into question the rather consistent results of the single- and multi-pollutant non-seasonal models that show a significant positive association between PM10 and daily mortality. For the older-age group, dew point consistently shows a significant association with daily mortality in all models. Collinearity problems appear in the multi-pollutant seasonal and non-seasonal models such that a significant, positive PM10 coefficient is accompanied by a significant, negative coefficient of another ambient pollutant, and the identity of this other pollutant changes with season. The PM2.5 data set is half that of PM10. Identical-model runs for both data sets reveal instability in the pollutant coefficients, especially for the younger age group. The concern for the instability of the pollutant coefficients due to a small signal-to-noise ratio makes it impossible to ascertain credibly the relative associations of the fine- and coarse-particle modes with daily mortality. In this connection, we call for caution in the interpretation of model results for causal inference when the models use fully or partially estimated PM values to fill large data gaps.     

Differential pulmonary inflammation and in vitro cytotoxicity of size-fractionated fly ash particles from pulverized coal combustion

Exposure to airborne particulate matter (PM) has been associated with adverse health effects in humans. Pulmonary inflammatory responses were examined in CD1 mice after intratracheal instillation of 25 or 100 microg of ultrafine (< 0.2 microm), fine (< 2.5 microm), and coarse (> 2.5 microm) coal fly ash from a combusted Montana subbituminous coal, and of fine and coarse fractions from a combusted western Kentucky bituminous coal. After 18 hr, the lungs were lavaged and the bronchoalveolar fluid was assessed for cellular influx, biochemical markers, and pro-inflammatory cytokines. The responses were compared with saline and endotoxin as negative and positive controls, respectively. On an equal-mass basis, the ultrafine particles from combusted Montana coal induced a higher degree of neutrophil inflammation and cytokine levels than did the fine or coarse PM. The western Kentucky fine PM caused a moderate degree of inflammation and protein levels in bronchoalveolar fluid that were higher than the Montana fine PM. Coarse PM did not produce any significant effects. In vitro experiments with rat alveolar macrophages showed that of the particles tested, only the Montana ultrafine displayed significant cytotoxicity. It is concluded that fly ash toxicity is inversely related with particle size and is associated with increased sulfur and trace element content.     

Identification of sources of Phoenix aerosol by positive matrix factorization

Chemical composition data for fine and coarse particles collected in Phoenix, AZ, were analyzed using positive matrix factorization (PMF). The objective was to identify the possible aerosol sources at the sampling site. PMF uses estimates of the error in the data to provide optimum data point scaling and permits a better treatment of missing and below-detection-limit values. It also applies nonnegativity constraints to the factors. Two sets of fine particle samples were collected by different samplers. Each of the resulting fine particle data sets was analyzed separately. For each fine particle data set, eight factors were obtained, identified as (1) biomass burning characterized by high concentrations of organic carbon (OC), elemental carbon (EC), and K; (2) wood burning with high concentrations of Na, K, OC, and EC; (3) motor vehicles with high concentrations of OC and EC; (4) nonferrous smelting process characterized by Cu, Zn, As, and Pb; (5) heavy-duty diesel characterized by high EC, OC, and Mn; (6) sea-salt factor dominated by Na and Cl; (7) soil with high values for Al, Si, Ca, Ti, and Fe; and (8) secondary aerosol with SO4(-2) and OC that may represent coal-fired power plant emissions. For the coarse particle samples, a five-factor model gave source profiles that are attributed to be (1) sea salt, (2) soil, (3) Fe source/motor vehicle, (4) construction (high Ca), and (5) coal-fired power plant. Regression of the PM mass against the factor scores was performed to estimate the mass contributions of the resolved sources. The major sources for the fine particles were motor vehicles, vegetation burning factors (biomass and wood burning), and coal-fired power plants. These sources contributed most of the fine aerosol mass by emitting carbonaceous particles, and they have higher contributions in winter. For the coarse particles, the major source contributions were soil and construction (high Ca). These sources also peaked in winter.     

Temporal analysis of airborne particulate matter reveals a dose-rate effect on mortality in El Paso: indications of differential toxicity for different particle mixtures

One of two topics explored is the limitations of the daily average in summarizing pollutant hourly profiles. The daily average of hourly measurements of air pollutant constituents provides continuity with previous studies using monitoring technology that only provided the daily average. However, other summary statistics are needed that make better use of all available information in 24-hr profiles. The daily average reflects the total daily dose, obscuring hourly resolution of the dose rate. Air pollutant exposures with comparable total daily doses may have very different effects when occurring at high levels over a few hours as opposed to low levels over a longer time. Alternative data-based choices for summary statistics are provided using principal component analysis to capture the exposure dose rate, while preserving ease of interpretation. This is demonstrated using the earliest hourly particle concentration data available for El Paso from archived records of particulate matter (PM)10. In this way, a significant association between evening PM10 exposures and nonaccidental daily mortality is found in El Paso from 1992 to 1995, otherwise missed using the daily average. Secondly, the nature and, hence, effects of particles in the ambient aerosol during El Paso sandstorms is believed different from that of particles present during still-air conditions resulting from atmospheric temperature inversions. To investigate this, wind speed (ws) is used as a surrogate variable to label PM10 exposures as Low-ws (primarily fine particles), High-ws (primarily coarse particles), or Mid-ws (a mixture of fine and coarse particles). A High-ws evening is significantly associated with a 10% lower risk of mortality on the succeeding third day, as compared with comparable exposures at Low- or Mid-ws. Although this analysis cannot be used to form firm conclusions because it uses a very small data set, it demonstrates the limitations of the daily average and suggests differential toxicity for different particle compositions.     

Synopsis of the temporal variation of particulate matter composition and size

A synopsis of the detailed temporal variation of the size and number distribution of particulate matter (PM) and its chemical composition on the basis of measurements performed by several regional research consortia funded by the U.S. Environmental Protection Agency (EPA) PM Supersite Program is presented. This program deployed and evaluated a variety of research and emerging commercial measurement technologies to investigate the physical and chemical properties of atmospheric aerosols at a level of detail never before achieved. Most notably these studies demonstrated that systematic size-segregated measurements of mass, number, and associated chemical composition of the fine (PM2.5) and ultrafine (PM0.1) fraction of ambient aerosol with a time resolution down to minutes and less is achievable. A wealth of new information on the temporal variation of aerosol has been added to the existing knowledge pool that can be mined to resolve outstanding research and policy-related questions. This paper explores the nature of temporal variations (on time scales from several minutes to hours) in the chemical and physical properties of PM and its implications in the identification of PM formation processes, and source attribution (primary versus secondary), the contribution of local versus transported PM and the development of effective PM control strategies. The PM Supersite results summarized indicate that location, time of day, and season significantly influence not only the mass and chemical composition but also the size-resolved chemical/elemental composition of PM. Ambient measurements also show that ultrafine particles have different compositions and make up only a small portion of the PM mass concentration compared with inhalable coarse and fine particles, but their number concentration is significantly larger than their coarse or fine counterparts. PM size classes show differences in the relative amounts of nitrates, sulfates, crustal materials, and most especially carbon as well as variations in seasonal and diurnal patterns.     

Particulate composition characteristics under different ambient air quality conditions

Particulate compositions including elemental carbon (EC), organic carbon (OC), water-soluble ionic species, and elemental compositions were investigated during the period from 2004 to 2006 in southern Taiwan. The correlation between the pollutant standard index (PSI) of ambient air quality and the various particle compositions was also addressed in this study. PSI revealed a correlation with fine (r = 0.74) and coarse (r = 0.80) particulate matter (PM). PSI manifested a significant correlation with the amount of analyzed ionic species (r approximately 0.80) in coarse and fine particles and a moderate correlation with carbon content (r = 0.63) in fine particles; however, it showed no correlation with elemental content. Although the ambient air quality ranged from good to moderate, the ionic species including chloride (Cl-), nitrate (NO3-), sulfate (SO4(2-)), sodium (Na+), ammonium (NH4+), magnesium (Mg2+), and calcium (Ca2+) increased significantly (1.5-3.7 times for Daliao and 1.8-6.9 times for Tzouying) in coarse PM. For fine particles, NO3-, SO4(2-), NH4+, and potassium (K+) also increased significantly (1.3-2.4 times for Daliao and 2.8-9.6 times for Tzouying) when the air quality went from good to moderate. For meteorological parameters, temperature evidenced a slightly negative correlation with PM concentration and PSI value, which implied a high PM concentration in the low-temperature condition. This reflects the high frequency of PM episodes in winter and spring in southern Taiwan. In addition, the mixing height increase from 980 to 1450 m corresponds to the air quality condition changing from unhealthy to good.     

Air Pollution and Mortality: The Implications of Uncertainties in Regression Modeling and Exposure Measurement

In a previous paper,¹ we showed that the mean effects on daily mortality associated with air pollution are essentially the same for gases and particulate matter (PM) and are invariant with respect to particle size and composition, based on 27 statistical studies that had been published at that time. Since then, a new analysis² reported stronger mortality associations for the fine fractions of PM obtained from dichotomous samplers, relative to the coarse fractions. In this paper, we show that differential measurement errors known to be present in dichotomous sampler data preclude reliable determination of such statistical relationships by particle size. Further, it is necessary to consider gaseous pollutants simultaneously with particles to provide robust estimates of the responsibilities for the implied daily mortality gradients. Finally, certain regression model specifications may be sensitive to differences in frequency distribution characteristics according to particle size.     

Comparison of particle size distributions and elemental partitioning from the combustion of pulverized coal and residual fuel oil

U.S. Environmental Protection Agency (EPA) research examining the characteristics of primary PM generated by the combustion of fossil fuels is being conducted in efforts to help determine mechanisms controlling associated adverse health effects. Transition metals are of particular interest, due to the results of studies that have shown cardiopulmonary damage associated with exposure to these elements and their presence in coal and residual fuel oils. Further, elemental speciation may influence this toxicity, as some species are significantly more water-soluble, and potentially more bio-available, than others. This paper presents results of experimental efforts in which three coals and a residual fuel oil were combusted in three different systems simulating process and utility boilers. Particle size distributions (PSDs) were determined using atmospheric and low-pressure impaction as well as electrical mobility, time-of-flight, and light-scattering techniques. Size-classified PM samples from this study are also being utilized by colleagues for animal instillation experiments. Experimental results on the mass and compositions of particles between 0.03 and > 20 microns in aerodynamic diameter show that PM from the combustion of these fuels produces distinctive bimodal and trimodal PSDs, with a fine mode dominated by vaporization, nucleation, and growth processes. Depending on the fuel and combustion equipment, the coarse mode is composed primarily of unburned carbon char and associated inherent trace elements (fuel oil) and fragments of inorganic (largely calcium-alumino-silicate) fly ash including trace elements (coal). The three coals also produced a central mode between 0.8- and 2.0-micron aerodynamic diameter. However, the origins of these particles are less clear because vapor-to-particle growth processes are unlikely to produce particles this large. Possible mechanisms include the liberation of micron-scale mineral inclusions during char fragmentation and burnout and indicates that refractory transition metals can contribute to PM < 2.5 microns without passing through a vapor phase. When burned most efficiently, the residual fuel oil produces a PSD composed almost exclusively of an ultrafine mode (approximately 0.1 micron). The transition metals associated with these emissions are composed of water-soluble metal sulfates. In contrast, the transition metals associated with coal combustion are not significantly enriched in PM < 2.5 microns and are significantly less soluble, likely because of their association with the mineral constituents. These results may have implications regarding health effects associated with exposure to these particles.     

A study on variations of concentrations of particulate matter with different sizes in Lanzhou,China

Lanzhou is one of the most air-polluted cities in China and in the world, and its primary air pollutant is particulate matter (PM). Different size particulate matter (TSP, PM₁₀, PM_2.5 and PM_1.0) have different sources and affect the environment and human health differently, so it is very important to study the pollutant characteristics of different particles in order to deeply understand the pollution situation of Lanzhou city and establish reasonable preventive countermeasures. TSP, PM₁₀, PM_2.5 and PM_1.0 concentrations were simultaneously measured in Lanzhou to detect the annual and diurnal variations of concentrations of PM with different sizes and possible causes. The main results are as follows: (1) The annual distribution of monthly average concentrations for coarse particles (TSP and PM₁₀) is bimodal with the highest peak in April, which is different from the situation in other cities not affected by sand-dust events. However, the annual distribution for fine particles (PM_2.5 and PM_1.0) is unimodal with the peak in December. This difference between coarse and fine particles indicates that sand-dust events in spring carry much more coarse than fine particles to Lanzhou. This result is supported by the correlation between springtime wind speed and concentrations of PM with different sizes. (2) Under normal conditions (without dust intrusions), the diurnal distribution of coarse particle concentration in Lanzhou is bimodal. However, the distribution is trimodal during dust intrusions in April, with an extra peak in the afternoon. (3) In general, the highest concentration peaks of the diurnal variations for TSP, PM₁₀, PM_2.5 and PM_1.0 occur at about the same time. However, there are obvious differences in the occurrence time of the minimum concentrations among different kinds of PM. The differences in the occurrence time of minima between coarse and fine particles are due to their different diffusion behaviors in the atmospheric boundary layer.     

Identification of Sources of Phoenix Aerosol by Positive Matrix Factorization

ABSTRACT

Chemical composition data for fine and coarse particles collected in Phoenix, AZ, were analyzed using positive matrix factorization (PMF). The objective was to identify the possible aerosol sources at the sampling site. PMF uses estimates of the error in the data to provide optimum data point scaling and permits a better treatment of missing and below-detection-limit values. It also applies nonnegativity constraints to the factors. Two sets of fine particle samples were collected by different samplers. Each of the resulting fine particle data sets was analyzed separately. For each fine particle data set, eight factors were obtained, identified as (1) biomass burning characterized by high concentrations of organic carbon (OC), elemental carbon (EC), and K; (2) wood burning with high concentrations of Na, K, OC, and EC; (3) motor vehicles with high concentrations of OC and EC; (4) nonferrous smelting process characterized by Cu, Zn, As, and Pb; (5) heavy-duty diesel characterized by high EC, OC, and Mn; (6) sea-salt factor dominated by Na and Cl; (7) soil with high values for Al, Si, Ca, Ti, and Fe; and (8) secondary aerosol with SO₄ ^-2 and OC that may represent coal-fired power plant emissions.

For the coarse particle samples, a five-factor model gave source profiles that are attributed to be (1) sea salt, (2) soil, (3) Fe source/motor vehicle, (4) construction (high Ca), and (5) coal-fired power plant. Regression of the PM mass against the factor scores was performed to estimate the mass contributions of the resolved sources. The major sources for the fine particles were motor vehicles, vegetation burning factors (biomass and wood burning), and coal-fired power plants. These sources contributed most of the fine aerosol mass by emitting carbonaceous particles, and they have higher contributions in winter. For the coarse particles, the major source contributions were soil and construction (high Ca). These sources also peaked in winter.     

Characterization of atmospheric particulates, particle-bound transition metals and polycyclic aromatic hydrocarbons of urban air in the centre of Athens (Greece)

The concentrations of trace metals and polycyclic aromatic hydrocarbons (PAHs) adsorbed to total suspended particulate (TSP) and finer fractions of airborne particulate matter (PM) were determined from a site in the centre of Athens (Greece), which is characterized by heavy local traffic and is densely populated, during the winter and summer periods in 2003-2004. Also, we collected and analyzed samples of diesel and gasoline exhaust particles from local vehicles (buses, taxis and private cars) and from chimney exhaust of residential central heating appliances. A seasonal effect was observed for the size distribution of aerosol mass, with a shift to larger fine fractions in winter. The most commonly detected trace metals in the TSP and PM fractions were Fe, Pb, Zn, Cu, Cr, V, Ni and Cd and their concentrations were similar to levels observed in heavily polluted urban areas from local traffic and other anthropogenic emissions. Analysis of 16 PAHs bound to PM showed that they are mostly traffic related. In general, the fine particulate PAHs concentrations were higher than coarse particles. The most common PAHs in PM(10.2) and PM(2.1) were pyrene, phenanthrene, acenapthylene and fluoranthene, which are associated with diesel and gasoline exhaust particles. The results of this study underlined the importance of local emission sources, especially vehicular traffic, central heating and other local anthropogenic emissions. Compared with other big cities, Athens has much higher levels of airborne particles, especially of the finer fractions PM(10) and PM(2.5), correlated with traffic-related air pollution.     

Chemical characterization and source identification/apportionment of fine and coarse air particles in Thessaloniki,Greece

The distribution of air particulate mass and selected particle components (trace elements and polycyclic aromatic hydrocarbons (PAHs)) in the fine and the coarse size fractions was investigated at a traffic-impacted urban site in Thessaloniki, Greece. 76±6% on average of the total ambient aerosol mass was distributed in the fine size fraction. Fine-sized trace elemental fractions ranged between 51% for Fe and 95% for Zn, while those of PAHs were between 95% and 99%. A significant seasonal effect was observed for the size distribution of aerosol mass, with a shift to larger fine fractions in winter. Similar seasonal trend was exhibited by PAHs, whereas larger fine fractions in summer were shown by trace elements. The compositional signatures of fine and coarse particle fractions were compared to that of local paved-road dust. A strong correlation was found between coarse particles and road dust suggesting strong contribution of resuspended road dust to the coarse particles. A multivariate receptor model (multiple regression on absolute principal component scores) was applied on separate fine and coarse aerosol data for source identification and apportionment. Results demonstrated that the largest contribution to fine-sized aerosol is traffic (38%) followed by road dust (28%), while road dust clearly dominated the coarse size fraction (57%).     

Windblown dust contributes to high PM2.5 concentrations

The revised National Ambient Air Quality Standards for PM include fine particulate standards based upon mass measurements of PM2.5. It is possible in arid and semi-arid regions to observe significant coarse mode intrusion in the PM2.5 measurement. In this work, continuous PM10, PM2.5, and PM1.0 were measured during several windblown dust events in Spokane, WA. PM2.5 constituted approximately 30% of the PM10 during the dust event days, compared with approximately 48% on the non-dusty days preceding the dust events. Both PM10 and PM2.5 were enhanced during the dust events. However, PM1.0 was not enhanced during dust storms that originated within the state of Washington. During a dust storm that originated in Asia and impacted Spokane, PM1.0 was also enhanced, although the Asian dust reached Washington during a period of stagnation and poor dispersion, so that local sources were also contributing to high particulate levels. The "intermodal" region of PM, defined as particles ranging in aerodynamic size from 1.0 to 2.5 microns, was found to represent a significant fraction of PM2.5 (approximately 51%) during windblown dust events, compared with 28% during the non-dusty days before the dust events.     

Effect of meteorological parameters on fine and coarse particulate matter mass concentration in a coal-mining area in Zonguldak, Turkey

In this work, the effect of meteorological parameters and local topography on mass concentrations of fine (PM2.5) and coarse (PM2.5-10) particles and their seasonal behavior was investigated. A total of 236 pairs of samplers were collected using an Anderson Dichotomous sampler between December 2004 and October 2005. The average mass concentrations of PM2.5, PM2.5-10, and particulate matter less than 10 microm in aerodynamic diameter (PM10) were found to be 29.38, 23.85, and 53.23 microg/m3, respectively. The concentrations of PM2.5 and PM10 were found to be higher in heating seasons (December to May) than in summer. The increase of relative humidity, cloudiness, and lower temperature was found to be highly related to the increase of particulate matter (PM) episodic events. During non-rainy days, the episodic events for PM2.5 and PM10 were increased by 30 and 10.7%, respectively. This is a result of the extensive use of fuel during winter for heating purposes and also because of stagnant air masses formed because of low temperature and low wind speed over the study area.     

Proinflammatory effect of fine and ultrafine particulate matter using size-resolved urban aerosols from Paris

Epidemiological and experimental studies have underlined that exposure to particulate matter (PM) leads mainly to airway inflammation, but the roles of particle size and chemical composition associated to such adverse health outcomes need to be better investigated. This study was performed to validate novel strategies of particle sampling, recovery and cell exposure in order to evaluate the pro-inflammatory potential of fine and ultrafine particles from a fractionated aerosol. Samplings of Paris background aerosols using 13-stage low pressure impactors (0.03-10 microm) gave bimodal mass distributions with an accumulation mode centered on a median diameter of 0.42 microm and a coarse one on 3.25 microm. PM 1 accounted for 70% and PM 0.1 for 12% of PM 10. The latter mainly comprised carbon-chained aggregates. The development of an efficient and reproducible method to recover fine (PM 1-0.1) and ultrafine (PM 0.1-0.03) particulate matter has permitted experimental comparison of the impact of such particles on human bronchial epithelial cells (HBECs). In this study we have compared the relative effects of fine and ultrafine particles at non-cytotoxic concentrations over 24h on the production of the pro-inflammatory cytokine GM-CSF by HBECs. Combining two cell exposure strategies to the size-fraction particles according to either their proportion (isovolume exposure) or their quantity in the aerosol (isomass exposure), we showed that both ultrafine and fine particles induced a concentration-dependent GM-CSF release by HBECs which is significant from 1 microg cm(-2). In conclusion, short duration samplings using 13-stage impactors enable to obtain size-resolved PM in sufficient quantities to carry out toxicological investigations. These findings are promising in view to conduct a more intensive study joining chemical and toxicological assays.     

Inorganic and carbonaceous components in indoor/outdoor particulate matter in two residential houses in Oslo, Norway

A detailed analysis of indoor/outdoor physicochemical aerosol properties has been performed. Aerosol measurements were taken at two dwellings, one in the city center and the other in the suburbs of the Oslo metropolitan area, during summer/fall and winter/spring periods of 2002-2003. In this paper, emphasis is placed on the chemical characteristics (water-soluble ions and carbonaceous components) of fine (PM2.5) and coarse (PM2.5-10) particles and their indoor/outdoor relationship. Results demonstrate that the carbonaceous species were dominant in all fractions of the PM10 particles (cut off size: 0.09-11.31 microm) during all measurement periods, except winter 2003, when increased concentrations of water-soluble inorganic ions were predominant because of sea salt transport. The concentration of organic carbon was higher in the fine and coarse PM10 fractions indoors, whereas elemental carbon was higher indoors only in the coarse fraction. In regards to the carbonaceous species, local traffic and secondary organic aerosol formation were, probably, the main sources outdoors, whereas indoors combustion activities such as preparation of food, burning of candles, and cigarette smoking were the main sources. In contrast, the concentrations of water-soluble inorganic ions were higher outdoors than indoors. The variability of water-soluble inorganic ion concentrations outdoors was related to changes in emissions from local anthropogenic sources, long-range transport of particles, sea salt emissions, and resuspension of roadside and soil dusts. In the indoor environment the infiltration of the outdoor air indoors was the major source of inorganic ions.     

Impact of banning of two-stroke engines on airborne particulate matter concentrations in Dhaka, Bangladesh

Vehicular air pollution is common in growing metropolitan areas throughout the world. Vehicular emissions of fine particles are particularly harmful because they occur near ground level, close to where people live and work. Two-stroke engines represented an important contribution to the motor vehicle emissions where they constitute approximately half of the total vehicle fleet in Dhaka city. Two-stroke engines have lower fuel efficiency than four-stroke engines, and they emit as much of an order of magnitude and more particulate matter (PM) than four-stroke engines of similar size. To eliminate their impact on air quality, the government of Bangladesh promulgated an order banning all two-stroke engines from the roads in Dhaka starting on December 31, 2002. The effect of the banning of two-stroke engines on airborne PM was studied at the Farm Gate air quality-monitoring station in Dhaka (capital of Bangladesh), a hot spot with very high-pollutant concentrations because of its proximity to major roadways. The samples were collected using a "Gent" stacked filter unit in two fractions of 0-2.2 microm and 2.2-10 microm sizes. Samples of fine and coarse fractions of airborne PM collected from 2000 to 2004 were studied. It has been found that the fine PM and black carbon concentrations decreased from the previous years because of the banning of two-stroke engine baby taxies.