Daily Air Pollution Levels Research Articles

Traffic-related air pollution and cardiovascular mortality in central Taiwan

In this study, the relationship between cardiovascular mortality and traffic-related air pollutants (NO2, CO, PM10, and six volatile organic compounds (VOCs), propane, iso-butane, propylene, benzene, meta-, para-, and ortho-xylenes) was investigated. The concentrations of NO2, PM10 and CO from 1993 to 2006 were measured at a fixed-site air monitoring station, and VOC data from 2003 to 2006 were obtained from a photochemical assessment monitoring site in an urban area in central Taiwan. Outcome variables were data on mortality due to cardiovascular diseases (ICD-9-CM 410–411, 414, 430–437) from 1993 to 2006. Cardiovascular mortality averaged 1.5 cases, ranging between 0 and 9 cases per day. Daily air pollution levels ranged from 0.5 to 80.5ppb for NO2 and from 0.1 to 3.8ppm for CO. From the subset of data from 2003 to 2006, daily average values ranged from 0.6 to 17.5ppb for propane, 0.3 to 6.7ppb for iso-butane, 0.3 to 6.7ppb for propylene, 0.2 to 3.8ppb for benzene, 0.3 to 26.0ppb for m,p-xylene, and 0.02 to 7.6ppb for o-xylene. Poisson generalized additive model was used to estimate the effects of elevated air pollutant levels on daily mortality, adjusting for meteorological conditions and temporal trends. Single-pollutant model showed that cardiovascular mortality was significantly associated with NO2 lagged 2days, and with propane, iso-butane, and benzene lagged 0day. The relative risk for an interquartile range increase in air pollutant levels was 1.053 for NO2, 1.064 for propane, 1.055 for iso-butane, and 1.055 for benzene. In conclusion, daily cardiovascular mortality showed association with data on acute exposure to traffic air pollutants in Taichung, which is an important factor to consider in studying cardiovascular mortality in urban environments.

Carbon monoxide pollution is associated with decreased lung function in asthmatic adults

The aim of the present study was to test the effects of exposure to air pollutants on lung function. A panel of 19 adult asthmatics living in Padua (Italy) was followed for five 30-day periods during 2 yrs consecutively (1,492 morning and 1,434 evening measures analysed). Peak expiratory flow (PEF) and forced expiratory volume in 1 s (FEV(1)) were measured using a pocket electronic meter. Daily levels of air pollutants and meteorological variables were collected at outdoor city monitoring sites. Significant inverse associations were observed between morning and evening PEF and carbon monoxide level (p = 0.01-0.03), without clear differences between lags (0-3 days). An increment of 1 mg.m(-3) CO was associated with a PEF variation ranging -2.6- -2.8%. All effect estimates on PEF for CO remained significant and even increased after controlling for particles with a 50% cut-off aerodynamic diameter of 10 microm (PM(10)), nitrogen dioxide and sulphur dioxide in single and multi-pollutant models. A similar trend was observed for FEV(1), but the associations were nonsignificant. A nonsignificant inverse relationship between evening PEF and SO(2) was also detected. PEF and FEV(1) were not related to PM(10) and NO(2) concentrations. The present results indicate that, in this panel of adult asthmatics, the worsening of lung function is associated with exposure to gaseous pollutants and occurs at levels of CO and SO(2) lower than current European standards.

Are the Short-term Effects of Air Pollution Restricted to Cardiorespiratory Diseases?

Short-term effects of air pollution on common morbidity are largely unknown. The authors explored links between daily levels of air pollution (nitrogen dioxide, ozone, and particulate matter less than 10 microm in diameter (PM(10))) and medical home visits made for diverse reasons in Bordeaux, France, during 2000-2006. Daily numbers of visits were obtained from a network of general practitioners. The excess relative risk (ERR) of a visit for each indicator associated with increased pollutant levels was estimated by fitting a Poisson regression model, controlling for well-known confounding factors and temporal trends. Positive and significant associations were found between air pollution and most health indicators. A 10-microg/m(3) increase in PM(10) levels was associated with increases in visits for upper and lower respiratory diseases (ERRs were 1.5% (95% confidence interval (CI): 0.3, 2.7) and 2.5% (95% CI: 0.5, 4.4), respectively), headache and asthenia (ERR = 3.5%, 95% CI: 1.3, 5.9), and skin rash and conjunctivitis (ERR = 3.2%, 95% CI: -0.2, 6.8). Significant associations were also found between nitrogen dioxide and ozone and several health indicators. Distributed-lag models showed no harvesting effect, and some effects persisted up to 15 days after exposure increased. These results suggest that considering only the most severe effects of air pollution leads to underestimation of its impact on public health.

The relationship of short-term air pollution and weather to ED visits for asthma in Japan

Introduction The incidence of asthma exacerbation has been increasing in many countries. Environmental factors may play an important role in this trend. We aimed to investigate the relationship of weather conditions and air pollution to significant exacerbation of asthma. Methods The daily number of emergency department (ED) visits by ambulance for asthma was collected through records of the Tokyo Fire Department from January 1 to December 31, 2005. We also collected daily air pollution levels and meteorological data for Tokyo during the same period. Meteorological data included minimum temperature, maximum barometric pressure, maximum relative humidity, and precipitation. Measured air pollutants included sulfur dioxide, nitrogen monoxide, nitrogen oxides, suspended particulate matter, and carbon monoxide. We performed a time series analysis using multivariable-adjusted autoregressive integrated moving average model. The analysis was conducted separately among adults and among children (<15 years old). Results Of a total of 643 849 patients who were transported to the ED by ambulance, there were 6447 patients with exacerbation of asthma. Among adults, lower minimum temperature was significantly associated with increased transport. Among children, there were no significant associations between exacerbation of asthmas requiring emergency transport and air pollutants or meteorological factors. The highest number of transports was found on October 11, the day after the National Sports Day in Japan. Conclusions Cold temperature is related to an increased risk of significant exacerbation of asthma in adults. Air pollution does not seem to play a major role in significant exacerbation of asthma requiring ambulance transports to ED.

Ambient Air Pollution and Daily Mortality Among Survivors of Myocardial Infarction

Certain subgroups in the general population, such as persons with existing cardiovascular or respiratory disease, may be more likely to experience adverse health effects from air pollution. In this European multicenter study, 25,006 myocardial infarction (MI) survivors in 5 cities were recruited from 1992 to 2002 via registers, and daily mortality was followed for 6 to 12 years in relation to ambient particulate and gaseous air pollution exposure. Daily air pollution levels were obtained from central monitor sites, and particle number concentrations were measured in 2001 and estimated retrospectively based on measured pollutants and meteorology. City-specific effect estimates from time-series analyses with Poisson regression were pooled over all 5 cities. Particle number concentrations and PM10 averaged over 2 days (lag 0-1) were associated with increased total nontrauma mortality for patients of age 35 to 74 (5.6% [95% confidence interval, 2.8%-8.5%] per 10,000/cm and 5.1% [1.6%-9.3%] per 10 microg/m, respectively). For longer averaging times (5 and 15 days), carbon monoxide and nitrogen dioxide were also associated with mortality. There were no clear associations with ozone or sulfur dioxide. Exposure to traffic-related air pollution was associated with daily mortality in MI survivors. Point estimates suggest a stronger effect of air pollution in MI survivors than among the general population.

Short-term Associations of Air Pollution with Postneonatal Infant Death in Seoul, Korea, 1999-2003

Objective to assess whether exposure to air pollutants is associated with postneonatal infant death, using a timeseries methodology, between 1999 and 2003 in Seoul, Korea.. Methods We investigated the short-term effects of air pollution for 548,725 live births during the study period. The daily count of postneonatal infant deaths from all causes and from SIDS (sudden infant death syndrome) by birth order was analyzed by a Generalized Additive Poisson model, with controlling for the effects of seasonal trends, air temperature, relative humidity, barometric pressure, and day of the week as covariates. Results During the study period, we observed 699 deaths from all causes and 47 deaths from SIDS. We did not find any significant associations between daily mortality and ambient levels of air pollutants except for CO and <TEX>$NO_2$</TEX>. The estimated relative risk of postneonatal infant death from all causes was 1.17 (95% CI=1.04-1.32) and 1.16 (95% CI=1.03-1.29) by IQR (interquartile range) for CO and <TEX>$NO_2$</TEX> respectively. Also, we observed no clear trend of the mortality effects of air pollution by birth orders. Conclusion In conclusion, our findings suggest that air pollution, in general, influenced adversely postneonatal infant death from all-cause and SIDS although it was not statistically significant. This study may support that the rationale.

Ambient air pollution triggers wheezing symptoms in infants

Background:There is limited evidence for the role of air pollution in the development and triggering of wheezing symptoms in young children. A study was undertaken to examine the effect of...

Do pollution time-series studies contain uncontrolled or residual confounding by risk factors for acute health events?

Acute health effects from air pollution are based largely on weak associations identified in time-series studies comparing daily air pollution levels to daily mortality. Much of this mortality is due to cardiovascular disease. Time-series studies have many potential limitations, but are not thought to be confounded by traditional cardiovascular risk factors (e.g., smoking status or hypertension) because these chronic risk factors are not obviously associated with daily pollution levels. However, acute psychobehavioral variants of these risk factors (e.g., smoking patterns and episodes of stress on any given day) are plausible confounders for the associations observed in time-series studies, given that time-series studies attempt to predict acute rather than chronic health outcomes. There is a fairly compelling literature on the strong link between cardiovascular events and daily “triggers” such as stress. Stress-related triggers are plausibly associated with daily pollution levels through surrogate stressors such as ambient temperature, daily workload, local traffic congestion, or other correlates of air pollution. For example, variables such as traffic congestion and industrial activity increase both stress-related health events and air pollution, suggesting the potential for classical confounding. Support for this argument is illustrated through examples of the well-demonstrated relationship between emotional stress and heart attack/stroke.

Outdoor air pollution and emergency department visits for asthma among children and adults: A case-crossover study in northern Alberta, Canada

BackgroundRecent studies have observed positive associations between outdoor air pollution and emergency department (ED) visits for asthma. However, few have examined the possible confounding influence of aeroallergens, or reported findings among very young children.MethodsA time stratified case-crossover design was used to examine 57,912 ED asthma visits among individuals two years of age and older in the census metropolitan area of Edmonton, Canada between April 1, 1992 and March 31, 2002. Daily air pollution levels for the entire region were estimated from three fixed-site monitoring stations. Similarly, daily levels of aeroallergens were estimated using rotational impaction sampling methods for the period between 1996 and 2002. Odds ratios and their corresponding 95% confidence intervals were estimated using conditional logistic regression with adjustment for temperature, relative humidity and seasonal epidemics of viral related respiratory disease.ResultsPositive associations for asthma visits with outdoor air pollution levels were observed between April and September, but were absent during the remainder of the year. Effects were strongest among young children. Namely, an increase in the interquartile range of the 5-day average for NO2 and CO levels between April and September was associated with a 50% and 48% increase, respectively, in the number of ED visits among children 2 – 4 years of age (p < 0.05). Strong associations were also observed with these pollutants among those 75 years of age and older. Ozone and particulate matter were also associated with asthma visits. Air pollution risk estimates were largely unchanged after adjustment for aeroallergen levels.ConclusionOur findings, taken together, suggest that exposure to ambient levels of air pollution is an important determinant of ED visits for asthma, particularly among young children and the elderly.

Associations of Fine and Ultrafine Particulate Air Pollution With Stroke Mortality in an Area of Low Air Pollution Levels

Daily variation in outdoor concentrations of inhalable particles (PM(10) <10 microm in diameter) has been associated with fatal and nonfatal stroke. Toxicological and epidemiological studies suggest that smaller, combustion-related particles are especially harmful. We therefore evaluated the effects of several particle measures including, for the first time to our knowledge, ultrafine particles (<0.1 microm) on stroke. Levels of particulate and gaseous air pollution were measured in 1998 to 2004 at central outdoor monitoring sites in Helsinki. Associations between daily levels of air pollutants and deaths caused by stroke among persons aged 65 years or older were evaluated in warm and cold seasons using Poisson regression. There was a total of 1304 and 1961 deaths from stroke in warm and cold seasons, respectively. During the warm season, there were positive associations of stroke mortality with current- and previous-day levels of fine particles (<2.5 microm, PM(2.5)) (6.9%; 95% CI, 0.8% to 13.8%; and 7.4%; 95% CI, 1.3% to 13.8% for an interquartile increase in PM(2.5)) and previous-day levels of ultrafine particles (8.5%; 95% CI, -1.2% to 19.1%) and carbon monoxide (8.3; 95% CI, 0.6 to 16.6). Associations for fine particles were mostly independent of other pollutants. There were no associations in the cold season. Our results suggest that especially PM(2.5), but also ultrafine particles and carbon monoxide, are associated with increased risk of fatal stroke, but only during the warm season. The effect of season might be attributable to seasonal differences in exposure or air pollution mixture.

Urban Air Pollution and Emergency Visits for Respiratory Complaints in Pisa, Italy

Emergency room visits for respiratory complaints, considered an indicator of deterioration of respiratory health, have been positively correlated to traffic-related air pollution. This is an ecological study to evaluate the association between daily levels of urban air pollutants and emergency visits for respiratory complaints, in children and the elderly residing in Pisa, Italy. Daily records of emergency department visits for respiratory complaints were selected from computerized registries, and paper medical reports were identified. Pollutant daily means were computed from hourly values obtained from the public network. Poisson regression, allowing for overdispersion and autocorrelation, was used to evaluate the percent change in daily visits associated with variations of air pollution measures. Among children, an increase in emergency visits of 10% (95% CL: 2.3; 18.2) was associated with a 10-μg/m3 increase in PM10 concentrations of the previous day and an increase of 11.8% (95% CL:1.4; 23.3) was associated with an analogous increment of NO2 during the 2 previous days. Among elderly the same increment of PM10 level during the 2 previous days was correlated with a 8.5% (95% CL: 1.5; 16.1) increase in the risk of recurring emergency department visits for respiratory complaints; this risk increased to 26.5% (95% CL: 3.4; 54.8) if the daily level of CO over the 4 previous days increased by 1 mg/m3. Evidence of morbidity related to short- and long-term air pollution exposures provided in this small study and larger studies conducted in other countries suggests the need for actions to improve air quality in any urban context.

Air pollution and inflammation in type 2 diabetes: a mechanism for susceptibility

Background: Particulate air pollution has been associated with several adverse cardiovascular health outcomes, and people with diabetes may be especially vulnerable. One potential pathway is inflammation and endothelial dysfunction—processes in...

Associations of Fine and Ultrafine Particulate Air Pollution with Specified Cardiovascular Causes of Death

P-030 Background: Particulate air pollution has been associated with cardiovascular mortality. Toxicological and epidemiological studies suggest that the smallest particles are especially harmful. However, there is a lack of long, continuous measurement series of finer particle fractions, especially ultrafine particles (<0.1 μm). We have daily data on ultrafine particle concentrations since 1998. Therefore, we examined the associations of daily levels of ultrafine and fine (<2.5 μm) particles with cause-specific cardiovascular mortality. Methods: Ultrafine particle number concentrations were monitored with a differential mobility particle sizer in 1998–2002 at a central outdoor monitoring site. Deaths due to all cardiovascular diseases (ICD-10: I00-I99; N=13 839), stroke (I60-I61, I63-I64; N=2783), ischemic heart diseases (I20-I25; N=8014) and other heart diseases (I30-I51; N=1167) were analyzed separately. The associations between daily levels of air pollution and deaths were evaluated using Poisson regression and controlling for time trend, temperature, relative humidity, barometric pressure, weekday and general holidays. Results: The median concentration for ultrafine particles was 9700 1/cm3 and for PM2.5 8.5 μg/m3. We found no consistent associations between ultrafine particles and mortality. There was some evidence of a positive association between fine particles and ‘other’ heart diseases with 4.15% (95% CI,1.3–9.9) increase in mortality for an interquartile increase in PM2.5 at lag 1. Conclusions: We found no strong associations between particulate air pollution and cardiovascular mortality when analyzing all seasons together. Based on our earlier experience on respiratory mortality, additional analyzes will be performed by warm and cold season separately.

A Daily Diary Panel Study of Congestive Heart Failure: Associations Between Health Outcomes and Air Pollution and Weather

P-019 Introduction: Time series studies of persons with congestive heart failure (CHF) suggest that their health may be affected greatly from exposure to ambient air pollution. The present daily diary panel study was conducted to determine whether there were associations between intermediate health outcomes (e.g., oxygen saturation) and exposure to daily levels of ambient air pollution and weather. Methods: Thirty-one subjects, over the age of 45 years (87% male), with a confirmed diagnosis of CHF were recruited from the Heart Failure Clinic of the Royal Victoria Hospital, Montreal, between 2002 and 2003. Over a two month period, subjects were asked every morning to record values of their oxygen saturation, pulse rate, body temperature, health status, and other factors that may affect their health. We had on hand daily averages of essential weather indicators and concentrations of criteria air pollutants as measured at fixed-site monitoring stations. Mixed linear regression using an AR1 error structure were used to model the various outcome variables according to daily personal covariates and average levels of air pollution and weather, after accounting for temporal trends (random effects). Results: From adjusted multilevel models, we found numerous effects in many of the health outcome variables under consideration. For example, for mean changes in oxygen saturation (assessed across interquartile ranges (IQ)): +0.098% (95%CI:0.032–0.163%) for an increase in barometric pressure from the previous day of 1.09kPa; -0.084% (95%CI:−0.165 – −0.004%) for increases in ozone of 23.73 μg/m3; and −0.259% (95%CI:−0.364 – −0.155%) for an increase in body temperature of 0.8° C. In other single pollutant, but otherwise adjusted models, associations with oxygen saturation were also found for SO2 (−0.104% (95%CI: −0.173 – −0.034%), IQ=8.59 μg/m3) and for PM2.5 (−0.066% (95%CI:−0.122 – −0.010%), IQ=7.28 μg/m3). Discussion and Conclusions: Our findings for body temperature and decreased barometric pressure are biologically coherent. The findings for air pollution are consistent with the results of time series studies that show that air pollution and weather affect mortality and hospitalizations. The effects found in this study are small, especially in comparison to what would be found from between-person comparisons, but reflect the expected smaller within-person temporal changes which were found to correlate with daily fluctuations. The mechanisms responsible for these effects may be related to some of the current theories of general and specific inflammation of air pollution as well as vasoconstriction that may be due to increases in endothelins.

Ambient Air Pollution and Cardiorespiratory Events in High-Risk Infants Using Home Monitors

TM6-O-01 Session Title: Air Pollution: Short-term Cardiovascular Effects Introduction: Identifying populations that are susceptible to the acute adverse health effects of ambient pollutants is a priority in air pollution research. The few studies that have examined infants suggest that ambient air pollution levels are associated with cardiorespiratory outcomes in this age group, but the studies have been generally limited in power and in health outcome information. The associations of daily ambient air pollution levels with apnea and bradycardia were examined in infants prescribed home cardiorespiratory monitors from 1998 through 2002, followed at one of the largest referral centers for home monitoring in the country. This is a novel population for air pollution studies and allows for examination of a potentially susceptible group. Methods: The monitors record the electrocardiogram, heart rate, and impedence for detected events. Collected data include type, date, time, and duration of each event, gender, date of birth, gestational age at birth, and birth weight. We assessed these events in relation to speciated particulate matter levels as well as gaseous air pollution levels, using a 2-day average of air pollution lagged zero and one day. Odds ratios (OR) and confidence intervals (CI) were calculated per standard deviation increase in pollution levels. Results: In preliminary analyses, 4277 infants had 8960 apnea event-days and 29,450 bradycardia event-days in over 179,000 days of follow-up. Our analysis used generalized estimating equations, controlling for time trends, temperature, age of the infant, weekends, and federal holidays as well as residual correlation within subject. Preliminary results show associations between bradycardia and ozone (OR, 1.049 per 25 ppb; 95% CI, 1.021–1.078) and nitrogen dioxide (OR, 1.025 per 20 ppb; 95% CI, 1.000–1.050). The association with ozone was robust to various methods of control for time trend and specified correlation structure. Associations with other pollutants, as well as associations for apnea events, were consistent with a null association. In secondary analyses, apnea events in full term and normal birth weight infants were associated with increased levels of the organic carbon component of fine particulate matter (OR = 1.091 per 2 μg/m3, 95% CI, 1.002–1.186); associations for preterm and low birth weight infants were consistent with a null association. Discussion: These results suggest that infants who are at high risk for apnea and bradycardia may be susceptible to the adverse health effects of ambient air pollution.

Associations between outdoor air pollution and emergency department visits for stroke in Edmonton, Canada

Inconsistent results have been obtained from studies that have examined the relationship between air pollution and hospital visits for stroke. We undertook a time-stratified case-crossover study to evaluate associations between outdoor air pollution and emergency department visits for stroke among the elderly according to stroke type, season, and sex. Analyses are based on a total of 12,422 stroke visits among those 65 years of age and older in Edmonton, Canada between April 1, 1992 and March 31, 2002. Daily air pollution levels for SO(2), NO(2), PM(2.5), PM(10), CO and O(3) were estimated using data from fixed-site monitoring stations. Particulate matter data were only available from 1998 onwards. Conditional logistic regression was used to estimate the odds ratios (ORs) and their 95% confidence intervals in relation to an increase in the interquartile range (IQR) of each pollutant. ORs were adjusted for the effects of temperature and relative humidity. We found no association between outdoor measures of air pollution and all stroke visits. In contrast, elevated risks were observed between levels of air pollution and acute ischemic stroke between April and September. During this season, the ORs associated with an increase in the IQR of the 3-day average for CO and NO(2) were 1.32 (95% CI = 1.09-1.60) and 1.26 (95% CI = 1.09-1.46), respectively. CO exposures in the same season, lagged 1 day, were associated with an increased risk of hemorrhagic stroke with ORs was 1.20 (95% CI = 1.00-1.43). Our results suggest it is possible that vehicular traffic, which produces increased levels of NO(2) and CO, contributes to an increased incidence of emergency department visits for stroke.

Associations of traffic related air pollutants with hospitalisation for first acute myocardial infarction: the HEAPSS study

Background: Acute myocardial infarction (AMI) is the leading cause of death attributed to cardiovascular diseases. An association between traffic related air pollution and AMI has been suggested, but the evidence...

The effects of air pollution on cardiovascular diseases: lag structures

To assess the lag structure between air pollution exposure and elderly cardiovascular diseases hospital admissions, by gender. Health data of people aged 64 years or older was stratified by gender in São Paulo city, Southeastern Brazil, from 1996 to 2001. Daily levels of air pollutants (CO, PM10, O3, NO2, and SO2) , minimum temperature, and relative humidity were also analyzed. It were fitted generalized additive Poisson regressions and used constrained distributed lag models adjusted for long time trend, weekdays, weather and holidays to assess the lagged effects of air pollutants on hospital admissions up to 20 days after exposure. Interquartile range increases in PM10 (26.21 microg/m(3)) and SO2 (10.73 microg/m(3)) were associated with 3.17% (95% CI: 2.09-4.25) increase in congestive heart failure and 0.89% (95% CI: 0.18-1.61) increase in total cardiovascular diseases at lag 0, respectively. Effects were higher among female group for most of the analyzed outcomes. Effects of air pollutants for different outcomes and gender groups were predominately acute and some "harvesting" were found. The results show that cardiovascular diseases in São Paulo are strongly affected by air pollution.

The impact of 9/11 on the association of ambient air pollution with daily respiratory hospital admissions in a Canada‐US border city, Windsor, Ontario

The 11 September 2001 (9/11) terrorist attacks in the United States resulted in long lines of trucks at the border crossing in Windsor, Ontario. Public concern about the potential impact of these trucks spewing toxic pollutants into the air drew attention to the need to investigate the impact of 9/11 on the daily levels of air pollutants and respiratory hospitalization. In this study, significant increases in respiratory admissions were found one month and 6 months post‐9/11. Mean daily respiratory admission was also significantly higher than the same period one year earlier and one year later. SO2 and CO concentration levels were found to be generally higher after 9/11 than one year before and immediately before. Relative risk estimates of respiratory hospitalization after 9/11 showed that SO2 ( = 1.15 for two‐day, = 1.18 for three‐day, and = 1.21 for five‐day averages), NO2 ( = 1.10 for current day), and COH ( = 1.09 for current day, = 1.10 for two‐day average) had the most significant effects after 9/11. These results suggest the need for more stringent regulatory efforts in air quality in the region in response to the changing transportation dynamics at this Canada‐US border crossing.

Is outdoor air pollution associated with physician visits for allergic rhinitis among the elderly in Toronto, Canada?

While a number of studies suggest that air pollution is associated with allergic rhinitis in children, findings among adults have been equivocal. The aim of this study was to examine the relationship between outdoor air pollution and physician visits for allergic rhinitis among individuals>or=65 years of age in Toronto, Canada. Physician visits were identified by using data from the Ontario provincial health insurance plan that is made available to all residents. Our analyses are based on 52,691 physician visits for allergic rhinitis among individuals>or=65 years of age in the Toronto metropolitan area between 1995 and 2000. Generalized linear models were used to regress daily counts of physician visits against daily measures of gaseous and particulate components of air pollution after controlling for seasonality, potential confounders (temperature, relative humidity, aeroallergens), overdispersion and serial correlation. A large number of comparisons were undertaken, with most showing no statistically significant associations between daily levels of air pollution and the number of physician visits for rhinitis. In contrast, an interquartile increase in the 10-day average of ragweed particles increased the mean number of daily rhinitis consultations by 6.4% (95% CI=0.7-12.4%). Our findings suggest that outdoor air pollution is a poor predictor of physician visits for allergic rhinitis among the elderly.