Air pollution and respiratory symptoms: results from three panel studies in Bangkok, Thailand.

Several studies in North American cities have reported associations between air pollution and respiratory symptoms. Replicating these studies in cities with very different population and weather characteristics is a useful way of addressing uncertainties and strengthening inferences of causality. To this end we examined the responses of three different panels to particulate matter (PM) air pollution in Bangkok, Thailand, a tropical city characterized by a very warm and humid climate. Panels of schoolchildren, nurses, and adults were asked to report daily upper and lower respiratory symptoms for 3 months. Concentrations of daily PM(10) (PM with a mass median aerodynamic diameter less than 10 microm) and PM(2.5) (airborne particles with aerodynamic diameters less than 2.5 microm) were collected at two sites. Generally, associations were found between these pollution metrics and the daily occurrence of both upper and lower respiratory symptoms in each of the panels. For example, an interquartile increase of 45 microg/m(3) in PM(10) was associated with about a 50% increase in lower respiratory symptoms in the panel of highly exposed adults, about 30% in the children, and about 15% in the nurses. These estimates were not appreciably altered by changes in the specification of weather variables, stratification by temperature, or inclusion of individual characteristics in the models; however, time trends in the data cause some uncertainty about the magnitude of the effect of PM on respiratory symptoms. These pollutants were also associated with the first day of a symptom episode in both adult panels but not in children. The estimated odds ratios are generally consistent with and slightly higher than the findings of previous studies conducted in the United States.

Indoor/outdoor PM10 and PM2.5 in Bangkok, Thailand.

Twenty-four-hour averaged PM10 and PM2.5 concentrations were obtained by using 4-liter-per-minute-pumps and impactors in microenvironments of a busy shopping district and a university hospital campus. In both areas, most people live directly adjacent to their worksites--minimizing the need to measure commuting exposure as part of total daily exposure. Co-located samplers were set in indoor microenvironments, the near-ambient zone of the households, and at nearby streetside central ambient monitoring stations. Smoking and use of other indoor PM sources were recorded daily via questionnaires. Consistent with previous studies, smoking and the use of charcoal stoves increased indoor particulate matter levels. The sampled air-conditioned hospital area had substantially lower particle concentrations than outdoors. A simple total exposure model was used to estimate the human exposure. The averaged ratios of co-located PM2.5/PM10 concentrations in various microenvironments are reported for each location. A single daily indoor average PM10 concentration for all households measured in a given sampling day is calculated for correlation analysis. Results showed that day-to-day fluctuations of these calculated indoor PM10 levels correlated well with near-ambient data and moderately well with ambient data collected at the nearby central monitoring site. This implies that ambient monitors are able to capture the daily variations of indoor PM levels or even personal exposure and may help explain the robust association of ambient PM levels and health effects found in many epidemiological studies. Absolute PM exposures, however, were substantially underestimated by ambient monitors in the shopping district, probably because of strong local sources.

Measuring heart patients' willingness to pay for changes in angina symptoms.

Willingness-to-pay (WTP) measures of the effects of changes in health on a person's welfare are more comprehensive than traditional cost-of-illness (COI) measures, but they are sometimes difficult to obtain. The authors investigated two approaches for measuring heart patients' WTP for changes in their angina symptoms. First, actual expenditures and perceived angina episodes avoided were used to infer an averting-behavior measurement of WTP. Second, a contingent-valuation approach was used to ask direct WTP questions regarding a hypothetical medical treatment that could be purchased to avoid additional angina episodes. The results indicated that although negligible COI changes were expected with small changes in angina frequency, the subjects had significant WTP to avoid increases in angina. The average WTP to avoid additional angina episodes revealed by the averting-behavior questions was comparable to the directly-elicited WTP, providing a test of the validity of the contingent-valuation approach.

Pulmonary function and ambient particulate matter: epidemiological evidence from NHANES I.

The relationship between pulmonary function and quarterly average levels of total suspended particulates (TSP) was examined for adults who resided in 49 of the locations where the First National Health and Nutrition Examination Survey (NHANES I) was conducted. Statistically significant relationships were observed between TSP levels and forced vital capacity (FVC) and forced expiratory volume at one second (FEV1.0). These relationships remained strong across several specifications and sample changes, e.g., exclusion of cities with two highest and two lowest TSP levels, restriction of sample to whites only. Anthropometric measurements and socioeconomic characteristics of the subjects were included in the analysis, and we restricted the sample to "never" smokers. The results indicate a 1 standard deviation increase (about 34 micrograms/m3) in TSP from the sample mean of 87 micrograms/m3 was associated with an average decrease in FVC of 2.25%. The results of this analysis also suggest that there is a threshold level (i.e., approximately 60 micrograms/m3 [quarterly average]) of TSP below which a relationship with pulmonary function ceases to exist.