An improved method for measuring aerosol strong acidity: Results from a nine-month study in St Louis, Missouri and Kingston, Tennessee

Review of health effects driven by aerosol acidity: Occurrence and implications for air pollution control

Acidity, generally expressed as pH, plays a crucial role in atmospheric processes and ecosystem evolution. Atmospheric acidic aerosol, triggering severe air pollution in the industrialization process (e.g., London Great Smoke in 1952), has detrimental effects on human health. Despite global endeavors to mitigate air pollution, the variation of aerosol acidity remains unclear and further restricts the knowledge of the acidity-driven toxicity of fine particles (PM2.5) in the atmosphere. Here, we summarize the toxicological effects and mechanisms of inhalable acidic aerosol and its response to air pollution control. The acidity could adjust toxic components (e.g., metals, quinones, and organic peroxides) bonded in aerosol and synergize with oxidant gaseous pollutants (e.g., O3 and NO2) in epithelial lining fluid to induce oxidative stress and inflammation. The inhaled aerosol from the ambient air with higher acidity might elevate airway responsiveness and cause worse pulmonary dysfunction. Furthermore, historical observation data and model simulation indicate that PM2.5 can retain its acidic property despite considerable reductions in acidifying gaseous pollutants (e.g., SO2 and NOx) from anthropogenic emissions, suggesting its continuing adverse impacts on human health. The study highlights that aerosol acidity could partially offset the health benefits of emission reduction, indicating that acidity-related health effects should be considered for future air pollution control policies.

Indoor acids and bases

Numerous acids and bases influence indoor air quality. The most abundant of these species are CO₂ (acidic) and NH₃ (basic), both emitted by building occupants. Other prominent inorganic acids are HNO₃ , HONO, SO₂ , H₂ SO₄ , HCl, and HOCl. Prominent organic acids include formic, acetic, and lactic; nicotine is a noteworthy organic base. Sources of N-, S-, and Cl-containing acids can include ventilation from outdoors, indoor combustion, consumer product use, and chemical reactions. Organic acids are commonly more abundant indoors than outdoors, with indoor sources including occupants, wood, and cooking. Beyond NH₃ and nicotine, other noteworthy bases include inorganic and organic amines. Acids and bases partition indoors among the gas-phase, airborne particles, bulk water, and surfaces; relevant thermodynamic parameters governing the partitioning are the acid-dissociation constant (K_a ), Henry's law constant (K_H ), and the octanol-air partition coefficient (K_oa ). Condensed-phase water strongly influences the fate of indoor acids and bases and is also a medium for chemical interactions. Indoor surfaces can be large reservoirs of acids and bases. This extensive review of the state of knowledge establishes a foundation for future inquiry to better understand how acids and bases influence the suitability of indoor environments for occupants, cultural artifacts, and sensitive equipment.

The Acidity of Atmospheric Particles and Clouds

Acidity, defined as pH, is a central component of aqueous chemistry. In the atmosphere, the acidity of condensed phases (aerosol particles, cloud water, and fog droplets) governs the phase partitioning of semi-volatile gases such as HNO3, NH3, HCl, and organic acids and bases as well as chemical reaction rates. It has implications for the atmospheric lifetime of pollutants, deposition, and human health. Despite its fundamental role in atmospheric processes, only recently has this field seen a growth in the number of studies on particle acidity. Even with this growth, many fine particle pH estimates must be based on thermodynamic model calculations since no operational techniques exist for direct measurements. Current information indicates acidic fine particles are ubiquitous, but observationally-constrained pH estimates are limited in spatial and temporal coverage. Clouds and fogs are also generally acidic, but to a lesser degree than particles, and have a range of pH that is quite sensitive to anthropogenic emissions of sulfur and nitrogen oxides, as well as ambient ammonia. Historical measurements indicate that cloud and fog droplet pH has changed in recent decades in response to controls on anthropogenic emissions, while the limited trend data for aerosol particles indicates acidity may be relatively constant due to the semi-volatile nature of the key acids and bases and buffering in particles. This paper reviews and synthesizes the current state of knowledge on the acidity of atmospheric condensed phases, specifically particles and cloud droplets. It includes recommendations for estimating acidity and pH, standard nomenclature, a synthesis of current pH estimates based on observations, and new model calculations on the local and global scale.

Highly Acidic Ambient Particles, Soluble Metals, and Oxidative Potential: A Link between Sulfate and Aerosol Toxicity

Soluble transition metals in particulate matter (PM) can generate reactive oxygen species in vivo by redox cycling, leading to oxidative stress and adverse health effects. Most metals, such as those from roadway traffic, are emitted in an insoluble form, but must be soluble for redox cycling. Here we present the mechanism of metals dissolution by highly acidic sulfate aerosol and the effect on particle oxidative potential (OP) through analysis of size distributions. Size-segregated ambient PM were collected from a road-side and representative urban site in Atlanta, GA. Elemental and organic carbon, ions, total and water-soluble metals, and water-soluble OP were measured. Particle pH was determined with a thermodynamic model using measured ionic species. Sulfate was spatially uniform and found mainly in the fine mode, whereas total metals and mineral dust cations were highest at the road-side site and in the coarse mode, resulting in a fine mode pH < 2 and near neutral coarse mode. Soluble metals and OP peaked at the intersection of these modes demonstrating that sulfate plays a key role in producing highly acidic fine aerosols capable of dissolving primary transition metals that contribute to aerosol OP. Sulfate-driven metals dissolution may account for sulfate-health associations reported in past studies.

Volcanic air pollution over the Island of Hawai'i: Emissions, dispersal, and composition. Association with respiratory symptoms and lung function in Hawai'i Island school children

BACKGROUND

Kilauea Volcano on the Island of Hawai'i has erupted continuously since 1983, releasing approximately 300-12000metrictons per day of sulfur dioxide (SO2). SO2 interacts with water vapor to produce an acidic haze known locally as "vog". The combination of wind speed and direction, inversion layer height, and local terrain lead to heterogeneous and variable distribution of vog over the island, allowing study of respiratory effects associated with chronic vog exposure.

OBJECTIVES

We characterized the distribution and composition of vog over the Island of Hawai'i, and tested the hypotheses that chronic vog exposure (SO2 and acid) is associated with increased asthma prevalence, respiratory symptoms, and reduced pulmonary function in Hawai'i Island schoolchildren.

METHODS

We compiled data of volcanic emissions, wind speed, and wind direction over Hawai'i Island since 1992. Community-based researchers then measured 2- to 4-week integrated concentrations of SO2 and fine particulate mass and acidity in 4 exposure zones, from 2002 to 2005, when volcanic SO2 emissions averaged 1600metrictons per day. Concurrently, community researchers recruited schoolchildren in the 4th and 5th grades of 25 schools in the 4 vog exposure zones, to assess determinants of lung health, respiratory symptoms, and asthma prevalence.

RESULTS

Environmental data suggested 4 different vog exposure zones with SO2, PM2.5, and particulate acid concentrations (mean±s.d.) as follows: 1) Low (0.3±0.2ppb, 2.5±1.2μg/m(3), 0.6±1.1nmolH+/m(3)), 2) Intermittent (1.6±1.8ppb, 2.8±1.5μg/m(3), 4.0±6.6nmolH+/m(3)), 3) Frequent (10.1±5.2ppb, 4.8±1.9μg/m(3), 4.3±6.7nmolH+/m(3)), and 4) Acid (1.2±0.4ppb, 7.2±2.3μg/m(3), 25.3±17.9nmolH+/m(3)). Participants (1957) in the 4 zones differed in race, prematurity, maternal smoking during pregnancy, environmental tobacco smoke exposure, presence of mold in the home, and physician-diagnosed asthma. Multivariable analysis showed an association between Acid vog exposure and cough and strongly suggested an association with FEV1/FVC <0.8, but not with diagnosis of asthma, or chronic persistent wheeze or bronchitis in the last 12months.

CONCLUSIONS

Hawai'i Island's volcanic air pollution can be very acidic, but contains few co-contaminants originating from anthropogenic sources of air pollution. Chronic exposure to acid vog is associated with increased cough and possibly with reduced FEV1/FVC, but not with asthma or bronchitis. Further study is needed to better understand how volcanic air pollution interacts with host and environmental factors to affect respiratory symptoms, lung function, and lung growth, and to determine acute effects of episodes of increased emissions.

Direct Measurement of pH in Individual Particles via Raman Microspectroscopy and Variation in Acidity with Relative Humidity

Atmospheric aerosol acidity is an important characteristic of aqueous particles, which has been linked to the formation of secondary organic aerosol by catalyzing reactions of oxidized organic compounds that have partitioned to the particle phase. However, aerosol acidity is difficult to measure and traditionally estimated using indirect methods or assumptions based on composition. Ongoing disagreements between experiments and thermodynamic models of particle acidity necessitate improved fundamental understanding of pH and ion behavior in high ionic strength atmospheric particles. Herein, Raman microspectroscopy was used to determine the pH of individual particles (H2SO4+MgSO4) based on sulfate and bisulfate concentrations determined from νs(SO4(2-)) and νs(HSO4(-)), the acid dissociation constant, and activity coefficients from extended Debye-Hückel calculations. Shifts in pH and peak positions of νs(SO4(2-)) and νs(HSO4(-)) were observed as a function of relative humidity. These results indicate the potential for direct spectroscopic determination of pH in individual particles and the need to improve fundamental understanding of ion behavior in atmospheric particles.

Chemical characteristics of aerosols and trace gas distribution over North and Central India

A field campaign on aerosol chemical properties and trace gases measurements was carried out along the Delhi-Hyderabad-Delhi road corridor (spanning about 3,200 km) in India, during February 1-29, 2004. Aerosol particles were collected on quartz and cellulose filters using high volume (PM(10)) sampler at various locations along the route (i.e., urban, semi-urban, rural, and forest areas) and have been characterized for major cations (Na(+), Ca(2+), Mg(2+), K(+), and NH (4) (+)), anions (Cl(-), NO (3)(-), and SO (4)(2-)), and heavy metals (Cu, Cd, Fe, Zn, Mn, and Pb). Simultaneously, we measured NO(2) and SO(2) gases. These species show large spatial and temporal variations. The ambient PM(10) concentration has been observed to be the highest (55 ± 4 μg m(-3)) near semi-urban areas followed by forest areas (48 ± 2 μg m(-3)) and in rural areas (44 ± 22 μg m(-3)). The concentrations of NO( x ) (NO(2)+NO) and SO(2) ranged from 16 to 69 μg m(-3) and 4 to 11 μg m(-3), respectively. Among anions, NO(3)(-) and SO(4) (2-) are the major constituents of PM(10). The urban and semi-urban sites showed enhanced concentrations of Fe, Zn, Mn, Cd, and Pb. This study provide information about atmospheric concentrations of various species in the northern to central India, which may be important for policy makers to better understand the air quality of the region.

Aged particles derived from emissions of coal-fired power plants: the TERESA field results

The Toxicological Evaluation of Realistic Emissions Source Aerosols (TERESA) study was carried out at three US coal-fired power plants to investigate the potential toxicological effects of primary and photochemically aged (secondary) particles using in situ stack emissions. The exposure system designed successfully simulated chemical reactions that power plant emissions undergo in a plume during transport from the stack to receptor areas (e.g., urban areas). Test atmospheres developed for toxicological experiments included scenarios to simulate a sequence of atmospheric reactions that can occur in a plume: (1) primary emissions only; (2) H(2)SO(4) aerosol from oxidation of SO(2); (3) H(2)SO(4) aerosol neutralized by gas-phase NH(3); (4) neutralized H(2)SO(4) with secondary organic aerosol (SOA) formed by the reaction of α-pinene with O(3); and (5) three control scenarios excluding primary particles. The aged particle mass concentrations varied significantly from 43.8 to 257.1 µg/m(3) with respect to scenario and power plant. The highest was found when oxidized aerosols were neutralized by gas-phase NH(3) with added SOA. The mass concentration depended primarily on the ratio of SO(2) to NO(x) (particularly NO) emissions, which was determined mainly by coal composition and emissions controls. Particulate sulfate (H(2)SO(4) + neutralized sulfate) and organic carbon (OC) were major components of the aged particles with added SOA, whereas trace elements were present at very low concentrations. Physical and chemical properties of aged particles appear to be influenced by coal type, emissions controls and the particular atmospheric scenarios employed.

Source apportionment of ambient fine particle size distribution using positive matrix factorization in Erfurt, Germany

Particle size distribution data collected between September 1997 and August 2001 in Erfurt, Germany were used to investigate the sources of ambient particulate matter by positive matrix factorization (PMF). A total of 29,313 hourly averaged particle size distribution measurements covering the size range of 0.01 to 3.0 microm were included in the analysis. The particle number concentrations (cm(-3)) for the 9 channels in the ultrafine range, and mass concentrations (ng m(-3)) for the 41 size bins in the accumulation mode and particle up to 3 microm in aerodynamic diameter were used in the PMF. The analysis was performed separately for each season. Additional analyses were performed including calculations of the correlations of factor contributions with gaseous pollutants (O(3), NO, NO(2), CO and SO(2)) and particle composition data (sulfate, organic carbon and elemental carbon), estimating the contributions of each factor to the total number and mass concentration, identifying the directional locations of the sources using the conditional probability function, and examining the diurnal patterns of factor scores. These results were used to assist in the interpretation of the factors. Five factors representing particles from airborne soil, ultrafine particles from local traffic, secondary aerosols from local fuel combustion, particles from remote traffic sources, and secondary aerosols from multiple sources were identified in all seasons.

Effect of acidity on secondary organic aerosol formation from isoprene

The effect of particle-phase acidity on secondary organic aerosol (SOA) formation from isoprene is investigated in a laboratory chamber study, in which the acidity of the inorganic seed aerosol was controlled systematically. The observed enhancement in SOA mass concentration is closely correlated to increasing aerosol acidity (R2 = 0.979). Direct chemical evidence for acid-catalyzed particle-phase reactions was obtained from the SOA chemical analyses. Aerosol mass concentrations for the 2-methyltetrols, as well as the newly identified sulfate esters, both of which serve as tracers for isoprene SOA in ambient aerosols, increased significantly with enhanced aerosol acidity. Aerosol acidities, as measured in nmol of H+ m(-3), employed in the present study are in the same range as those observed in tropospheric aerosol collected from the eastern U.S.

Semicontinuous measurements of organic carbon and acidity during the Pittsburgh Air Quality Study: implications for acid-catalyzed organic aerosol formation

Laboratory evidence suggests that inorganic acid seed particles may increase secondary organic aerosol yields secondary organic aerosol (SOA) through heterogeneous chemistry. Additional laboratory studies, however, report that organic acidity generated in the same photochemical process by which SOA is formed may be sufficient to catalyze these heterogeneous reactions. Understanding the interaction between inorganic acidity and SOA mass is important when evaluating emission controls to meet PM2.5 regulations. We examine semicontinuous measurements of organic carbon (OC), elemental carbon (EC), and inorganic species from the Pittsburgh Air Quality Study to determine if we can detect coupling in the variations of inorganic acidity and OC. We were not able to detect significant enhancements of SOA production due to inorganic acidity in Western Pennsylvania most of the time, but its signal might have been lost in the noise. If we assume a causal relationship between inorganic acidity and OC, reductions in OC for Western Pennsylvania that might result from drastic reductions in inorganic acidity were estimated to be 2 +/- 4% by a regression technique, and an upper bound for this geographic area was estimated to be 5 +/- 8% based on calculations from laboratory measurements.

Aerosol ion characteristics during the Big Bend Regional Aerosol and Visibility Observational study

The ionic compositions of particulate matter with aerodynamic diameter < or = 2.5 microm (PM2.5) and size-resolved aerosol particles were measured in Big Bend National Park, Texas, during the 1999 Big Bend Regional Aerosol and Visibility Observational study. The ionic composition of PM2.5 aerosol was dominated by sulfate (SO4(2-)) and ammonium (NH4+). Daily average SO4(2-) and NH4+ concentrations were strongly correlated (R2 = 0.94). The molar ratio of NH4+ to SO4(2-) averaged 1.54, consistent with concurrent measurements of aerosol acidity. The aerosol was observed to be comprised of a submicron fine mode consisting primarily of ammoniated SO4(2-) and a coarse particle mode containing nitrate (NO3-). The NO3- appears to be primarily associated with sea salt particles where chloride has been replaced by NO3-, although formation of calcium nitrate (Ca(NO3)2) is important, too, on several days. Size-resolved aerosol composition results reveal that a size cut in particulate matter with aerodynamic diameter < or = 1 microm would have provided a much better separation of fine and coarse aerosol modes than the standard PM2.5 size cut utilized for the study. Although considerable nitric acid exists in the gas phase at Big Bend, the aerosol is sufficiently acidic and temperatures sufficiently high that even significant future reductions in PM2.5 SO4(2-) are unlikely to be offset by formation of particulate ammonium nitrate in summer or fall.

Characterization of lead, cadmium, arsenic and nickel in PM(2.5) particles in the Athens atmosphere, Greece

Concentrations of Pb, Cd, As and Ni in PM(2.5) particles were measured in samples collected, using low volume PM(2.5) samplers (Harvard Impactor system, HI) at two sites in Athens basin; Patission Street in Athens city center and Rentis, a semi-urban and industrial area, during March 1995-March 1996. Sample analysis for Pb, Cd, Ni and As was accomplished by electrothermal atomic absorption spectrometry after total digestion. Annual geometric mean values in 183 PM(2.5) particles samples were found to be: Pb: 143 nanogram(-3); Cd: 0.34 nanogram(-3); Ni: 4.55 nanogram(-3); As: 0.79 nanogram(-3). The geographical and temporal distribution patterns were investigated. Pb exhibited higher values during the winter period. For the other elements no significant seasonal variation was observed. Wind direction, air temperature and relative humidity affected element concentrations. Principal component analysis was applied on the data to enable source apportionment of toxic elements in PM(2.5) particles. It was found that Pb, As and Ni have common sources, which could be vehicles emissions/oil combustion and resuspended road dust. Cd and a portion of As originate from industrial activities.

Atmospheric conversion of sulfur dioxide to particulate sulfate and nitrogen dioxide to particulate nitrate and gaseous nitric acid in an urban area

Sulfur dioxide, nitrogen dioxide, particulate sulfate and nitrate, gaseous nitric acid, ozone and meteorological parameters (temperature and relative humidity) were measured during the winter season (1999-2000) and summer season (2000) in an urban area (Dokki, Giza, Egypt). The average particulate nitrate concentrations were 6.20 and 9.80 microg m(-3), while the average gaseous nitric acid concentrations were 1.14 and 6.70 microg m(-3) in the winter and summer seasons, respectively. The average sulfate concentrations were 15.32 microg m(-3) during the winter and 25.10 microg m(-3) during the summer season. The highest average concentration ratio of gaseous nitric acid to total nitrate was found during the summer season. Particulate sulfate and nitrate and gaseous nitric acid concentrations were relatively higher in the daytime than those in the nighttime. Sulfur conversion ratio (Fs) and nitrogen conversion ratio (Fn) defined in the text were calculated from the field measurement data. Sulfur conversion ratio (Fs) and nitrogen conversion ratio (Fn) in the summer were about 2.22 and 2.97 times higher than those in the winter season, respectively. Moreover, sulfur conversion ratio (Fs) and nitrogen conversion ratio (Fn) were higher in the daytime than those in the nighttime during the both seasons. The sulfur conversion ratio (Fs) increases with increasing ozone concentration and relative humidity. This indicates that the droplet phase reactions and gas phase reactions are important for the oxidation of SO2 to sulfate. Moreover, the nitrogen conversion ratio (Fn) increases with increasing ozone concentration, and the gas phase reactions are important and predominant for the oxidation of NO2 to nitrate.

Lung inflammation induced by concentrated ambient air particles is related to particle composition

The objectives of this study were (1) to determine whether short-term exposures to concentrated air particles (CAPs) cause pulmonary inflammation in normal rats and rats with chronic bronchitis (CB); (2) to identify the site within the lung parenchyma where CAPs-induced inflammation occurs; and (3) to characterize the component(s) of CAPs that is significantly associated with the development of the inflammatory reaction. Four groups of animals were studied: (1) air treated, filtered air exposed (air-sham); (2) sulfur dioxide treated (CB), filtered air exposed (CB-sham); (3) air treated, CAPs exposed (air-CAPs); and (4) sulfur dioxide treated, CAPs exposed (CB-CAPs). CB and normal rats were exposed by inhalation either to filtered air or CAPs during 3 consecutive days (5 hours/day). Pulmonary inflammation was assessed by bronchoalveolar lavage (BAL) and by measuring the numerical density of neutrophils (Nn) in the alveolar walls at the bronchoalveolar junction and in more peripheral alveoli. CAPs (as a binary exposure term) and CAPs mass (in regression correlations) induced a significant increase in BAL neutrophils and in normal and CB animals. Nn in the lung tissue significantly increased with CAPs in normal animals only. Greater Nn was observed in the central compared with peripheral regions of the lung. A significant dose-dependent association was found between many CAPs components and BAL neutrophils or lymphocytes, but only vanadium and bromine concentrations had significant associations with both BAL neutrophils and Nn in CAPs-exposed groups analyzed together. Results demonstrate that short-term exposures to CAPs from Boston induce a significant inflammatory reaction in rat lungs, with this reaction influenced by particle composition.

Effects of environmental aerosols on airway hyperresponsiveness in a murine model of asthma

Increased morbidity in persons suffering from inflammatory lung diseases, such as asthma and bronchitis, has been associated with air pollution particles. One hypothesis is that particles can cause an amplification of the pulmonary inflammation associated with these diseases, thus worsening affected individuals' symptoms. This hypothesis was tested in a murine model of asthma by inhalation exposure to (1) concentrated air particles (CAPs), (2) the leachate of residual oil fly ash (ROFA-S), and (3) lipopolysaccharide (LPS). Allergen-sensitized mice (ip ovalbumin, OVA) were 21 days old when challenged with an aerosol of 3% OVA in phosphate-buffered saline (PBS) for 10 min (controls were challenged with PBS only) for 3 days. On the same days, mice were further exposed to 1 of 3 additional agents: CAPs (or filtered air) for 6 h/day; LPS (5 microg/ml, or PBS) for 10 min/day; or ROFA-S (leachate of 50 mg/ml, or PBS) for 30 min on day 2 only. At 24 h later, mice challenged with OVA aerosol showed airway inflammation and airway hyperresponsiveness (AHR) to methacholine (Mch), features absent in mice challenged with PBS alone. Both OVA- and PBS-challenged mice subsequently exposed to ROFA-S showed increased AHR to Mch when compared to their respective controls (OVA only or PBS only). In contrast, when OVA-challenged mice were further exposed to CAPs or LPS, no changes in AHR were seen in comparison to mice challenged with OVA only. Bronchoalveolar lavage (BAL) analysis and histopathology 48 h postexposure showed OVA-induced allergic inflammation. No significant additional effects were caused by CAPs or ROFA-S. LPS, in contrast, caused significant increases in total cell, macrophage, and polymorphonuclear cell numbers. The data highlight discordance between airway inflammation and hyperresponsiveness.

Response of a grassland ecosystem to air pollutants. IV. The chemical climate: concentrations of relevant non-criteria pollutants (trace gases and aerosols)

The concentrations of sulphur dioxide, nitric acid, nitrous acid, hydrogen chloride, ammonia and sulphate, nitrate, chloride and ammonium in aerosols were measured continuously for two years at the rural site of Rotenkamp near Braunschweig in south-east Lower Saxony. The level of air pollution registered is typical for rural areas near industrial areas in Central Europe. Long-range transport of polluted air masses from Saxony-Anhalt and Saxony affects air quality when high-pressure areas over Eastern Europe result in easterly winds and reduced vertical exchange due to low inversion layers.

An association between air pollution and mortality in six U.S. cities

BACKGROUND

Recent studies have reported associations between particulate air pollution and daily mortality rates. Population-based, cross-sectional studies of metropolitan areas in the United States have also found associations between particulate air pollution and annual mortality rates, but these studies have been criticized, in part because they did not directly control for cigarette smoking and other health risks.

METHODS

In this prospective cohort study, we estimated the effects of air pollution on mortality, while controlling for individual risk factors. Survival analysis, including Cox proportional-hazards regression modeling, was conducted with data from a 14-to-16-year mortality follow-up of 8111 adults in six U.S. cities.

RESULTS

Mortality rates were most strongly associated with cigarette smoking. After adjusting for smoking and other risk factors, we observed statistically significant and robust associations between air pollution and mortality. The adjusted mortality-rate ratio for the most polluted of the cities as compared with the least polluted was 1.26 (95 percent confidence interval, 1.08 to 1.47). Air pollution was positively associated with death from lung cancer and cardiopulmonary disease but not with death from other causes considered together. Mortality was most strongly associated with air pollution with fine particulates, including sulfates.

CONCLUSIONS

Although the effects of other, unmeasured risk factors cannot be excluded with certainty, these results suggest that fine-particulate air pollution, or a more complex pollution mixture associated with fine particulate matter, contributes to excess mortality in certain U.S. cities.

Air pollution and daily mortality: associations with particulates and acid aerosols

The association between total daily mortality and air pollution was investigated for a 1-year period (September 1985 through August 1986) in St. Louis and in the counties in eastern Tennessee surrounding Kingston/Harriman. The purpose of this study was to evaluate the relative importance of various measures of particulate and gaseous air pollution as predictors of daily mortality. Concentrations of inhalable particles (PM10), fine particles (PM2.5), the elemental composition of these particles, and aerosols acidity were measured daily during the period of study. The effect of each air pollutant on daily mortality was estimated after controlling for meteorologic and seasonal influences. Total mortality in St. Louis was found to increase 16% (95% CI-1 to 33%) for each 100 micrograms/m3 increase in PM10, and by 17% (95% CI-12 to 57%) in eastern Tennessee. Positive but progressively weaker associations were found with PM2.5, sulfate, and aerosol acidity concentrations in both communities. Associations with gaseous pollutants--sulfur dioxide, nitrogen dioxide, and ozone--were all far from statistical significance. Because of the short monitoring period for daily particulate air pollution, the power of this study to detect associations was limited. Nevertheless, statistically significant associations with PM10 were found in St. Louis, and, more importantly, the estimated effects were consistent between the two communities studied and with other reported analyses of the effects of particles on daily mortality. These data suggest that the acidity of particles is not as important in associations with daily mortality as the mass concentrations of particles.

Long-term intermittent exposure to sulfuric acid aerosol, ozone, and their combination: alterations in tracheobronchial mucociliary clearance and epithelial secretory cells

Understanding the effects from long-term exposure to individual ambient air pollutants and mixtures of pollutants is necessary for adequate assessment of health risk. This study examined quantitative and temporal alterations in tracheobronchial mucociliary clearance function and bronchial epithelial secretory cells in rabbits exposed to sulfuric acid (125 micrograms/m3), ozone (0.1 ppm), and their combination for 2 h/d, 5 d/wk for up to 1 yr; some animals were allowed a 6-month post-exposure period. Clearance times were altered during exposure to sulfuric acid or to the mixture, and became progressively slower following the end of exposures to each of the pollutant atmospheres. There was no indication of any interaction in terms of clearance response between the acid and ozone in the group exposed to the mixture. Histological examination of intrapulmonary conducting airways was performed after 4, 8, or 12 months of exposure, and after the post-exposure period. Sulfuric acid resulted in an increase in the number of secretory cells in small airways by 12 months of exposure. Ozone and the mixture resulted in an increase in secretory cell number by 4 months, but the response became attenuated with continued exposure. There was evidence for synergistic interaction between ozone and acid at 4 months, and antagonistic interaction at subsequent times. No inflammation or other biologically significant histological effects were found in any of the animals.

Daily mortality and PM10 pollution in Utah Valley

The association between daily mortality and respirable particulate pollution (PM10) in Utah County was assessed from April 1985 through December 1989. Poisson regression analysis was used to regress daily death counts on PM10 pollution levels, controlling for variability in the weather. A significant positive association between nonaccidental mortality and PM10 pollution was observed. The strongest association was with 5-d moving average PM10 levels, including the concurrent day and the preceding 4 d. An increase in 5-d moving average PM10 levels, equal to 100 micrograms/m3, was associated with an estimated increase in deaths per day equal to 16%. The association with mortality and PM10 was largest for respiratory disease deaths, next largest for cardiovascular deaths, and smallest for all other deaths. Mean PM10 concentrations during the study period equaled 47 micrograms/m3. The maximum 24-h and 5-d moving average PM10 levels equaled 365 and 297 micrograms/m3, respectively. Relatively low levels of sulfur dioxide, aerosol acidity, and ozone suggested an independent association between mortality and PM10. The relative risk of death increased monotonically with PM10, and the relationship was observed at PM10 levels that were well below the current National Ambient Air Quality Standard of 150 micrograms/m3.

Asthmatic responses to airborne acid aerosols

BACKGROUND

Controlled exposure studies suggest that asthmatics may be more sensitive to the respiratory effects of acidic aerosols than individuals without asthma. This study investigates whether acidic aerosols and other air pollutants are associated with respiratory symptoms in free-living asthmatics.

METHODS

Daily concentrations of hydrogen ion (H+), nitric acid, fine particulates, sulfates and nitrates were obtained during an intensive air monitoring effort in Denver, Colorado, in the winter of 1987-88. A panel of 207 asthmatics recorded respiratory symptoms, frequency of medication use, and related information in daily diaries. We used a multiple regression time-series model to analyze which air pollutants, if any, were associated with health outcomes reported by study participants.

RESULTS

Airborne H+ was found to be significantly associated with several indicators of asthma status, including moderate or severe cough and shortness of breath. Cough was also associated with fine particulates, and shortness of breath with sulfates. Incorporating the participants' time spent outside and exercise intensity into the daily measure of exposure strengthened the association between these pollutants and asthmatic symptoms. Nitric acid and nitrates were not significantly associated with any respiratory symptom analyzed.

CONCLUSIONS

In this population of asthmatics, several outdoor air pollutants, particularly airborne acidity, were associated with daily respiratory symptoms.