Ambient particulate air pollution and cardiac arrhythmia in a panel of older adults in Steubenville, Ohio.

OBJECTIVES: Ambient particulate air pollution has been associated with increased risk of cardiovascular morbidity and mortality. Pathways by which particles may act involve autonomic nervous system dysfunction or inflammation, which can affect cardiac rate and rhythm. The importance of these pathways may vary by particle component or source. In an eastern US location with significant regional pollution, the authors examined the association of air pollution and odds of cardiac arrhythmia in older adults. METHODS: Thirty two non-smoking older adults were evaluated on a weekly basis for 24 weeks during the summer and autumn of 2000 with a standardised 30 minute protocol that included continuous electrocardiogram measurements. A central ambient monitoring station provided daily concentrations of fine particles (PM(2.5), sulfate, elemental carbon) and gases. Sulfate was used as a marker of regional pollution. The authors used logistic mixed effects regression to examine the odds of having any supraventricular ectopy (SVE) or ventricular ectopy (VE) in association with increases in air pollution for moving average pollutant concentrations up to 10 days before the health assessment. RESULTS: Participant specific mean counts of arrhythmia over the protocol varied between 0.1-363 for SVE and 0-350 for VE. The authors observed odds ratios for having SVE over the length of the protocol of 1.42 (95% CI 0.99 to 2.04), 1.70 (95% CI 1.12 to 2.57), and 1.78 (95% CI 0.95 to 3.35) for 10.0 microg/m3, 4.2 microg/m3, and 14.9 ppb increases in five day moving average PM2.5, sulfate, and ozone concentrations respectively. The other pollutants, including elemental carbon, showed no effect on arrhythmia. Participants reporting cardiovascular conditions (for example, previous myocardial infarction or hypertension) were the most susceptible to pollution induced SVE. The authors found no association of pollution with VE. CONCLUSION: Increased levels of ambient sulfate and ozone may increase the risk of supraventricular arrhythmia in the elderly.

Laboratory and field evaluation of measurement methods for one-hour exposures to O3, PM2.5, and CO.

While researchers have linked acute (less than 12-hr) ambient O3, PM2.5, and CO concentrations to a variety of adverse health effects, few studies have characterized short-term exposures to these air pollutants, in part due to the lack of sensitive, accurate, and precise sampling technologies. In this paper, we present results from the laboratory and field evaluation of several new (or modified) samplers used in the "roll-around" system (RAS), which was developed to measure 1-hr O3, PM2.5, and CO exposures simultaneously. All the field evaluation data were collected during two sampling seasons: the summer of 1998 and the winter of 1999. To measure 1-hr O3 exposures, a new active O3 sampler was developed that uses two nitrite-coated filters to measure O3 concentrations. Laboratory chamber tests found that the active O3 sampler performed extremely well, with a collection efficiency of 0.96 that did not vary with temperature or relative humidity (RH). In field collocation comparisons with a reference UV photometric monitor, the active O3 sampler had an effective collection efficiency ranging between 0.92 and 0.96 and a precision for 1-hr measurements ranging between 4 and 6 parts per billion (ppb). The limits of detection (LOD) of this method were 9 ppb-hr for the chamber tests and approximtely 16 ppb-hr for the field comparison tests. PM2.5 and CO concentrations were measured using modified continuous monitors--the DustTrak and the Langan, respectively. A size-selective inlet and a Nafion dryer were placed upstream of the DustTrak inlet to remove particles with aerodynamic diameters greater than 2.5 microm and to dry particles prior to the measurements, respectively. During the field validation tests, the DustTrak consistently reported higher PM2.5 concentrations than those obtained by the collocated 12-hr PM2.5 PEM samples, by approximately a factor of 2. After the DustTrak response was corrected (correction factor of 2.07 in the summer and 2.02 in the winter), measurements obtained using these methods agreed well with R2 values of 0.87 in the summer and 0.81 in the winter. The results showed that the DustTrak can be used along with integrated measurements to measure the temporal and spatial variation in PM2.5 exposures. Finally, during the field validation tests, CO concentrations measured using the Langan were strongly correlated with those obtained using the reference method when the CO levels were above the LOD of the instrument [approximately 1 part per million (ppm)].

A pilot investigation of the relative toxicity of indoor and outdoor fine particles: in vitro effects of endotoxin and other particulate properties.

In this study we assessed the in vitro toxicity of 14 paired indoor and outdoor PM(2.5) samples (particulate matter < or =2.5 microm in aerodynamic diameter) collected in 9 Boston-area homes. Samples were collected as part of a large indoor particle characterization study that included the simultaneous measurement of indoor and outdoor PM(2.5), particle size distributions, and compositional data (e.g., elemental/organic carbon, endotoxin, etc.). Bioassays were conducted using rat alveolar macrophages (AMs), and tumor necrosis factor (TNF) was measured to assess particle-induced proinflammatory responses. Additional experiments were also conducted in which AMs were primed with lipopolysaccharides (LPS) to simulate preexisting pulmonary inflammation such as that which might exist in sick and elderly individuals. Significant TNF production above that of negative controls was observed for AMs exposed to either indoor or outdoor PM(2.5). TNF releases were further amplified for primed AMs, suggesting that preexisting inflammation can potentially exacerbate the toxicity of not only outdoor PM(2.5) (as shown by previous studies) but also indoor PM(2.5). In addition, indoor particle TNF production was found to be significantly higher than outdoor particle TNF production in unprimed AMs, both before and after normalization for endotoxin concentrations. Our results suggest that indoor-generated particles may be more bioactive than ambient particles. Endotoxin was demonstrated to mediate proinflammatory responses for both indoor and outdoor PM(2.5), but study findings suggest the presence of other proinflammatory components of fine particles, particularly for indoor-generated particles. Given these study findings and the fact that people spend 85-90% of their time indoors, future studies are needed to address the toxicity of indoor particles.

Gaseous pollutants in particulate matter epidemiology: confounders or surrogates?

Air pollution epidemiologic studies use ambient pollutant concentrations as surrogates of personal exposure. Strong correlations among numerous ambient pollutant concentrations, however, have made it difficult to determine the relative contribution of each pollutant to a given health outcome and have led to criticism that health effect estimates for particulate matter may be biased due to confounding. In the current study we used data collected from a multipollutant exposure study conducted in Baltimore, Maryland, during both the summer and winter to address the potential for confounding further. Twenty-four-hour personal exposures and corresponding ambient concentrations to fine particulate matter (PM(2.5)), ozone, nitrogen dioxide, sulfur dioxide, and carbon monoxide were measured for 56 subjects. Results from correlation and regression analyses showed that personal PM(2.5) and gaseous air pollutant exposures were generally not correlated, as only 9 of the 178 individual-specific pairwise correlations were significant. Similarly, ambient concentrations were not associated with their corresponding personal exposures for any of the pollutants, except for PM(2.5), which had significant associations during both seasons (p < 0.0001). Ambient gaseous concentrations were, however, strongly associated with personal PM(2.5) exposures. The strongest associations were shown between ambient O(3) and personal PM(2.5) (p < 0.0001 during both seasons). These results indicate that ambient PM(2.5) concentrations are suitable surrogates for personal PM(2.5) exposures and that ambient gaseous concentrations are surrogates, as opposed to confounders, of PM(2.5). These findings suggest that the use of multiple pollutant models in epidemiologic studies of PM(2.5) may not be suitable and that health effects attributed to the ambient gases may actually be a result of exposures to PM(2.5).

Using time- and size-resolved particulate data to quantify indoor penetration and deposition behavior.

Because people spend approximately 85-90% of their time indoors, it is widely recognized that a significant portion of total personal exposures to ambient particles occurs in indoor environments. Although penetration efficiencies and deposition rates regulate indoor exposures to ambient particles, few data exist on the levels or variability of these infiltration parameters, in particular for time- and size-resolved data. To investigate ambient particle infiltration, a comprehensive particle characterization study was conducted in nine nonsmoking homes in the metropolitan Boston area. Continuous indoor and outdoor PM2.5 and size distribution measurements were made in each of the study homes over weeklong periods. Data for nighttime, nonsource periods were used to quantify infiltration factors for PM2.5 as well as for 17 discrete particle size intervals between 0.02 and 10 microns. Infiltration factors for PM2.5 exhibited large intra- and interhome variability, which was attributed to seasonal effects and home dynamics. As expected, minimum infiltration factors were observed for ultrafine and coarse particles. A physical-statistical model was used to estimate size-specific penetration efficiencies and deposition rates for these study homes. Our data show that the penetration efficiency depends on particle size as well as home characteristics. These results provide new insight on the protective role of the building shell in reducing indoor exposures to ambient particles, especially for tighter (e.g., winterized) homes and for particles with diameters greater than 1 micron.

Criteria air pollutants and toxic air pollutants.

This review presents a brief overview of the health effects and exposures of two criteria pollutants--ozone and particulate matter--and two toxic air pollutants--benzene and formaldehyde. These pollutants were selected from the six criteria pollutants and from the 189 toxic air pollutants on the basis of their prevalence in the United States, their physicochemical behavior, and the magnitude of their potential health threat. The health effects data included in this review primarily include results from epidemiologic studies; however, some findings from animal studies are also discussed when no other information is available. Health effects findings for each pollutant are related in this review to corresponding information about outdoor, indoor, and personal exposures and pollutant sources.

Assessing the relationship between personal particulate and gaseous exposures of senior citizens living in Baltimore, MD.

We conducted a multi-pollutant exposure study in Baltimore, MD, in which 15 non-smoking older adult subjects (> 64 years old) wore a multi-pollutant sampler for 12 days during the summer of 1998 and the winter of 1999. The sampler measured simultaneous 24-hr integrated personal exposures to PM2.5, PM10, SO4(2-), O3, NO2, SO2, and exhaust-related VOCs. Results of this study showed that longitudinal associations between ambient PM2.5 concentrations and corresponding personal exposures tended to be high in the summer (median Spearman's r = 0.74) and low in the winter (median Spearman's r = 0.25). Indoor ventilation was an important determinant of personal PM2.5 exposures and resulting personal-ambient associations. Associations between personal PM2.5 exposures and corresponding ambient concentrations were strongest for well-ventilated indoor environments and decreased with ventilation. This decrease was attributed to the increasing influence of indoor PM2.5 sources. Evidence for this was provided by SO4(2-) measurements, which can be thought of as a tracer for ambient PM2.5. For SO4(2-), personal-ambient associations were strong even in poorly ventilated indoor environments, suggesting that personal exposures to PM2.5 of ambient origin are strongly associated with corresponding ambient concentrations. The results also indicated that the contribution of indoor PM2.5 sources to personal PM2.5 exposures was lowest when individuals spent the majority of their time in well-ventilated indoor environments. Results also indicate that the potential for confounding by PM2.5 co-pollutants is limited, despite significant correlations among ambient pollutant concentrations. In contrast to ambient concentrations, PM2.5 exposures were not significantly correlated with personal exposures to PM2.5-10, PM2.5 of non-ambient origin, O3, NO2, and SO2. Since a confounder must be associated with the exposure of interest, these results provide evidence that the effects observed in the PM2.5 epidemiologic studies are unlikely to be due to confounding by the PM2.5 co-pollutants measured in this study.

Hourly personal exposures to fine particles and gaseous pollutants--results from Baltimore, Maryland.

A study to characterize 1-hr multi-pollutant exposures was performed in Baltimore, MD, during the summer of 1998 and the winter of 1999, and was conducted over a 15-day period in each of the two seasons. Personal exposures were measured by a trained field technician, who wore a newly developed Roll-Around System (RAS) to measure 1-hr PM2.5 and gaseous (CO, O3, NO2, SO2, volatile organic compounds [VOCs]) exposures. One-hour O3, NO2, and SO2 personal exposures were measured using samplers developed in our laboratory, while short-term PM2.5, CO, and VOCs exposures were measured using currently available monitors. All 1-hr multi-pollutant exposures were measured while the technician performed pre-determined activities, beginning at 7:00 a.m. and ending at 7:00 p.m. of the same day. Activities were scripted to simulate activities performed by older adults (65+ years of age). Corresponding 1-hr ambient pollutant concentrations were obtained from federal or state monitoring networks. In this paper, we discuss the results from our study and present our descriptive analysis of the 1-hr personal particulate and gaseous exposure data. Personal PM2.5, O3, CO, and VOCs exposures showed substantial variability over the 12-hr sampling periods. Multiple pairwise comparison tests showed that 1-hr personal O3 exposures were significantly lower in indoor microenvironments as compared with outdoor microenvironments. One-hour personal CO exposures measured in vehicles were significantly higher than those measured in other microenvironments. The associations between 1-hr personal exposures and corresponding ambient concentrations differed by pollutant and by microenvironment. For example, the correlation between personal PM2.5 exposures and ambient concentrations was lowest (rs = 0.36, p < 0.05) in the winter for indoor non-residential microenvironments, and was highest (rs = 0.90, p < 0.05) in the winter for in-vehicle microenvironments. For O3, the correlation between personal exposures and ambient levels was weakest in the winter for residential microenvironments (rs = 0.05, p > 0.05), and was strongest in the summer for outdoor near-roadway microenvironments (rs = 0.91, p < 0.05).

Characterization of indoor particle sources using continuous mass and size monitors.

A comprehensive indoor particle characterization study was conducted in nine Boston-area homes in 1998 in order to characterize sources of PM in indoor environments. State-of-the-art sampling methodologies were used to obtain continuous PM2.5 concentration and size distribution particulate data for both indoor and outdoor air. Study homes, five of which were sampled during two seasons, were monitored over week-long periods. Among other data collected during the extensive monitoring efforts were 24-hr elemental/organic carbon (EC/OC) particulate data as well as semi-continuous air exchange rates and time-activity information. This rich data set shows that indoor particle events tend to be brief, intermittent, and highly variable, thus requiring the use of continuous instrumentation for their characterization. In addition to dramatically increasing indoor PM2.5 concentrations, these data demonstrate that indoor particle events can significantly alter the size distribution and composition of indoor particles. Source event data demonstrate that the impacts of indoor activities are especially pronounced in the ultrafine (da < or = 0.1 micron) and coarse (2.5 < or = da < or = 10 microns) modes. Among the sources of ultrafine particles characterized in this study are indoor ozone/terpene reactions. Furthermore, EC/OC data suggest that organic carbon is a major constituent of particles emitted during indoor source events. Whether exposures to indoor-generated particles, particularly from large short-term peak events, may be associated with adverse health effects will become clearer when biological mechanisms are better known.

Relationships among personal, indoor, and outdoor fine and coarse particle concentrations for individuals with COPD.

This study characterizes the personal, indoor, and outdoor PM2.5, PM10, and PM2.5-10 exposures of 18 individuals with chronic obstructive pulmonary disease (COPD) living in Boston, MA. Monitoring was performed for each participant for six consecutive days in the winters of 1996 or 1997 and for six to twelve days in the summer of 1996. On each day, 12-h personal, indoor, and outdoor samples of PM2.5 and PM10 were collected simultaneously. Home characteristic information and time-activity patterns were also obtained. Personal exposures were higher than corresponding indoor and outdoor concentrations for all particle measures and for all seasons, except for winter indoor PM2.5-10 levels, which were higher than personal and outdoor levels. Higher personal exposures may be due to the proximity of the individuals to particle sources, such as cooking and cleaning. Indoor concentrations were associated with both outdoor concentrations and personal exposures (as determined by individual least square regression analyses), with associations strongest for PM2.5. Indoor PM2.5 concentrations were significantly associated with outdoor and personal levels for 12 and 15 of the 17 individuals, respectively. Both the strength and magnitude of the associations varied by individual. Also, personal PM2.5, but not PM2.5-10, exposures were associated with outdoor levels, with 10 of the 17 subjects having significant associations. The strength of the personal-outdoor association for PM2.5 was strongly related to that for indoor and outdoor levels, suggesting that home characteristics and indoor particulate sources were key determinants of the personal-outdoor association for PM2.5. Air exchange rates were found to be important determinants of both indoor and personal levels. Again, substantial interpersonal variability in the personal-outdoor relationship was found, as personal exposures varied by as much as 200% for a given outdoor level.

Characterization of indoor particle sources: A study conducted in the metropolitan Boston area.

An intensive particle monitoring study was conducted in homes in the Boston, Massachusetts, area during the winter and summer of 1996 in an effort to characterize sources of indoor particles. As part of this study, continuous particle size and mass concentration data were collected in four single-family homes, with each home monitored for one or two 6-day periods. Additionally, housing activity and air exchange rate data were collected. Cooking, cleaning, and the movement of people were identified as the most important indoor particle sources in these homes. These sources contributed significantly both to indoor concentrations (indoor-outdoor ratios varied between 2 and 33) and to altered indoor particle size distributions. Cooking, including broiling/baking, toasting, and barbecuing contributed primarily to particulate matter with physical diameters between 0.02 and 0.5 microm [PM((0.02-0.5))], with volume median diameters of between 0.13 and 0.25 microm. Sources of particulate matter with aerodynamic diameters between 0.7 and 10 microm [PM((0.7-10))] included sautéing, cleaning (vacuuming, dusting, and sweeping), and movement of people, with volume median diameters of between 3 and 4.3 microm. Frying was associated with particles from both PM((0.02-0.5)) and PM((0.7-10)). Air exchange rates ranged between 0.12 and 24.3 exchanges/hr and had significant impact on indoor particle levels and size distributions. Low air exchange rates (< 1 exchange/hr) resulted in longer air residence times and more time for particle concentrations from indoor sources to increase. When air exchange rates were higher (> 1 exchange/hr), the impact of indoor sources was less pronounced, as indoor particle concentrations tracked outdoor levels more closely.

Color-image generation by use of binary-phase holograms.

A novel, simple scheme for producing full-color images by use of binary-phase holograms and red (632.8-nm), green (543.5-nm), and blue (488-nm), lasers is reported. The theory and experimental results of the system are also presented.

A minimally invasive technique of appendectomy using a minimal skin incision and laparoscopic instruments.

To take advantage of the laparoscopic procedure, a new minimally invasive technique of appendectomy for nonobese and uncomplicated appendicitis is presented. Initially, diagnostic laparoscopy is performed through a minimal skin incision (microceliotomy) 1.5-2.0 cm in length in the right lower abdomen to rule out other disease. Then an appendectomy is performed using conventional surgical instruments under direct vision through the previous skin incision. There were 18 women and 12 men in this series. The mean age was 22.6 years. Pathologic findings of the appendix were: 2 normal, 13 catarrhal, 10 suppurative, and 5 gangrenous type. The mean operation time was 30.7 min. The mean frequency of postoperative analgesic requirement (nalbuphine 0.2 mg/kg) was 0.9 times. The mean hospital stay was 4.1 days (range, 2-7 days), and the duration until return to full activity was 7.6 days (range, 5-14 days). There was no mortality or morbidity. This appendectomy technique is a useful method for minimizing the postoperative pain and operative scar, thus allowing the patient an early return to full activity.

The metropolitan acid aerosol characterization study: results from the summer 1994 Washington, D.C. field study.

An ambient particle monitoring study was conducted in Washington, D.C. during the summer of 1994 as part of the Metropolitan Acid Aerosol Characterization Study (MAACS). Acid aerosol and inhalable (particulate matter with aerodynamic diameters < 10 micron; PM10) and fine (particulate matter with aerodynamic diameters < 2.5 micron; PM2.5) particle samples were collected for 24-hr periods (9 A.M.-9 A.M. EDT) on alternate days at six monitoring sites located throughout the greater Washington, D.C. area. Monitoring sites were located in both urban and rural areas and were generally situated along a southwest to northeast line due to the prevailing winds. Information on site characteristics, including population density and distance from the city center, was also obtained, as were data on meteorological parameters. Results from this study show strong correlations among the particulate measures, PM10, PM2.5, SO4(2-), and H+. These strong correlations resulted from the fact that PM2.5 comprised 77% of PM10, with SO4(2-)-related species accounting for 49% of total PM2.5. PM10, PM2.5, SO4(2-), and H+ concentrations were found to be uniform across the metropolitan Washington area. Spatial variation was found, however, for coarse particles (PM2.5-10) and NH3 concentrations. In our previous Philadelphia study, population density was an important determinant of spatial variation in coarse particles and NH3 concentrations, however, in Washington, D.C., population density was not associated with observed spatial patterns in coarse particle concentrations, but was an important determinant of NH3 concentrations. When data from one site (Reservoir) was excluded from the analysis, population density explained larger percentage of the variability in NH3 levels and became an important determinant of the H+/SO4(2-) ratio as well. Ambient H+ models developed from Philadelphia data were found to predict H+ concentrations in Washington, D.C. reasonably well, representing an improvement over measurements made at a single stationary ambient monitoring site.

Fine particles and coarse particles: concentration relationships relevant to epidemiologic studies.

Fine particles and coarse particles are defined in terms of the modal structure of particle size distributions typically observed in the atmosphere. Differences between the various modes are discussed. The fractions of fine and coarse particles collected in specific size ranges, such as total suspended particulate matter (TSP), PM10, PM2.5, and PM(10-2.5), are shown. Correlations of 24-h concentrations of PM2.5, PM10, and PM(10-2.5) at the same site show that, in Philadelphia and St. Louis, PM2.5 is highly correlated with PM10 but poorly correlated with PM (10-2.5). Among sites distributed across these urban areas, the site-to-site correlations of 24-h PM concentrations are high for PM2.5 but not for PM(10-2.5). This indicates that a PM measurement at a central monitor can serve as a better indicator of the community-wide concentration of fine particles than of coarse particles. The fraction of ambient outdoor particles found suspended indoors is greater for fine particles than for coarse particles because of the difference in indoor lifetimes. Consideration of these relationships leads to the hypothesis that the statistical associations found between daily PM indicators and health outcomes may be the result of variations in the fine particle component of the atmospheric aerosol, not of variations in the coarse component. As a result, epidemiologic studies using PM10 or TSP may provide more useful information on the acute health effects of fine particles than coarse particles. Fine and coarse particles are separate classes of pollutants and should be measured separately in research and epidemiologic studies. PM2.5 and PM(10-2.5) are indicators or surrogates, but not measurements, of fine and coarse particles.

Dexamethasone and forskolin synergistically increase [Met5]enkephalin accumulation in mixed brain cell cultures.

Possible synergistic effects of the glucocorticoid dexamethasone (DEX, 10(-7) M) and the adenylate cyclase agonist forskolin (FSK, 10(-5) M) on [Met5]enkephalin (ME) accumulation were examined in enriched rat glial cultures and in mixed neuronal/glial cultures. In enriched glial cultures, DEX and FSK each stimulated the accumulation of ME 2-3-fold over basal media levels, but there was little additional stimulation when these agonists were combined. In contrast, mixed neuronal/glial cultures showed only weak responses to DEX or FSK alone, but the combination of these agonists produced a pronounced synergistic effect on media ME accumulation (6-10-fold over basal levels). The DEX effect was mediated via a classical glucocorticoid receptor, since DEX was potent (acting over a concentration range of 10(-11)-10(-7) M), mimicked by corticosterone (10(-6) M), and blocked by the glucocorticoid receptor antagonist RU486. There was a pronounced time lag (2 days) for the synergistic effects of DEX + FSK to develop. In situ hybridization and immunocytochemical studies suggested that astrocytes were the major source for the increased ME production in all mixed neuronal/glial cultures examined. Creating a mixed culture by plating fetal neurons onto confluent, enriched P7 glial cultures inhibited accumulation of ME in the media. DEX + FSK, but neither agonist alone, overcame this neuronal inhibition and increased accumulation of media ME to levels identical to levels in stimulated enriched glial cultures. The net effect was a 6-fold increase in ME accumulation in the mixed neuronal/glial cultures relative to a 2.5-fold increase in the enriched glial cultures. Neuronal inhibition of basal glial ME production could explain the similar synergistic effects of DEX + FSK observed in all mixed neuronal/glial cultures examined, and may be important in suppressing ME production by astrocytes in the brain.

Colorectal injury by compressed air--a report of 2 cases.

We report two colorectal trauma patients whose rectosigmoid region was ruptured due to a jet of compressed air directed to their anus while they were playing practical jokes with their colleagues in their place of work. It was difficult to diagnose in one patient due to vague symptoms and signs and due to being stunned by a stroke of the compressed air. Both patients suffered from abdominal pain and distension, tension pneumoperitoneum and mild respiratory alkalosis. One patient was treated with primary two layer closure, and the other with primary two layer closure and sigmoid loop colostomy. Anorectal manometry and transanal ultrasonography checked 4 weeks after surgery, revealed normal anorectal function and anatomy. The postoperative courses were favorable without any wound infection or intraabdominal sepsis.

Combined binary-phase holograms for free-space optical interconnection.

We have developed a combined binary-phase hologram (CBPH) consisting of two binary-phase holograms. The CBPH can be used effectively for optical interconnection and image processing because it suppresses the unwanted images of a conventional binary-phase hologram. The theory and properties of the CBPH and experimental results are presented.

The relationship between airborne acidity and ammonia in indoor environments.

Indoor acid aerosol, nitric acid (HNO3), and ammonia (NH3) concentrations were measured in 47 homes in State College, Pennsylvania, during the summer of 1991. From each home, 12-hour indoor, 12- and 24-hour outdoor, and 12-hour air exchange samples were collected continuously over a 5-day period. Additionally, questionnaires were administered daily by field technicians to obtain information on house occupant number, ventilation, gas stove use, pets, and other housing characteristics. In this paper, we discuss the relationship between NH3 and corresponding concentrations of aerosol strong acidity (H+) and HNO3 inside these homes. As part of this analysis, we also examined indoor/outdoor concentration relationships and identified housing factors that may influence indoor levels. In State College, indoor NH3 concentrations were higher than corresponding outdoor levels, with air conditioner use, air exchange rates, and occupant number identified as important determinants of indoor levels. Indoor concentrations of both H+ and HNO3 were substantially lower than outdoor levels, as homes with air exchange rates less than one exchange per hour were found to have essentially no acid indoors. These low H+ and HNO3 levels likely resulted from their reaction with indoor NH3 and with indoor surfaces. Indoor NH3 concentrations were higher than outdoor levels, indicating the presence of indoor NH3 sources; however, correlations between indoor NH3 and both pets and occupants, its primary indoor sources, were weak and negative, respectively. Mass balance models that included an NH3 neutralization term were found to predict indoor H+ concentrations reasonably well, representing a substantial improvement over outdoor concentrations alone. The accumulation of NH3 indoors was found to be the primary determinant of indoor H+ and HNO3 levels.