Environ. Scl. Technol. 1983, 17, 164-168
Rasmussen, R. A,; Rasmussen, L. E.; Khalil, M. A. K.; Dalluge, R. W. J. Geophys. Res. 1980,85, 7350-7356. Crutzen, P. J.; Heidt, L. E.; Krasnec, J. P.; Pollock, W. H.; Seiler, W. Nature (London) 1979,282, 253-256. Logan, J. A. “Proceedings of the NATO Advanced Study Institute on Atmospheric Ozone: Its Variations and Human Influences”; Aikin, A. C., Ed.; Department of Transportation: Washington, DC, 1980.
(33) Rahn, K. A., University of Rhode Island, personal communication, 1982. Received for review May 24,1982. Accepted November 29,1982. Financial support for this research was provided in part by grants from NASA (NSG 7457 and NAG 1 -16O), NSF (AMT-8109047), the Dow Chemical Co., Biospherics Research Corp., and the Andarz Co.
Nitrogen Dioxide Inside and Outside 137 Homes and Implications for Ambient Air Quality Standards and Health Effects Research John D. Spengler” Department of Environmental Health Sciences, Harvard School of Public Health, Boston, Massachusetts 021 15
Colin P. Duffy Department of Horticulture, University of Wisconsin, Madison, Wisconsin 53706
Richard Letz Department of Physiology, Harvard School of Public Health, Boston, Massachusetts 02115
Theodore W. Tibbitts Department of Horticulture, University of Wisconsin, Madison, Wisconsin 53706
Benjamin 0. Ferris, Jr. Department of Physiology, Harvard School of Public Health, Boston, Massachusetts 02115
Week-long integrated nitrogen dioxide (NO,) measurements were made by using diffusion tube samplers inside and outside 137 homes in Portage, WI, over a 1-year period. The annual mean ambient NO2 concentrations in this rural community were 10-15 pg/m3. NO2levels inside the kitchens of 112 homes with gas stoves averaged about 50 pg/m3 higher, and bedroom levels were about 30 pg/m3 higher, than outdoor levels. Ten percent of the gas-cooking homes had annual average kitchen NO2levels higher than the National Ambient Air Quality Standard of 100 pg/m3. NO2levels inside kitchens of 25 homes with electric stoves were about two-thirds outdoor levels, while corresponding bedroom levels were one-half outdoor levels. Distinct seasonal patterns (higher indoor levels in winter, lower in summer) consistent with changes in normal air-exchange rates were evident in gas-cooking homes. The large variation of NO2 concentrations among homes, likely due to differences in stove use, emission rates, and air-exchange rates, limits the development of prediction models. In addition, this variation would reduce the power of epidemiological studies of respiratory health, which use ambient NO2concentration levels, a simple dichotomous description of stove type and two categories of home cooking fuel to describe exposure.
Introduction Most nitrogen dioxide in the ambient atmosphere is produced by the oxidation of nitrogen oxide formed during high-temperature combustion. Nationally, automobiles and stationary fuel combustion are responsible for equal amounts of NO, emissions and together yield 95% of total estimated emissions. Annual ambient concentration averages range fsom 0.001 ppm in rural areas to approximately 0.08 ppm in some urban areas. While ambient air concentrations in most locations are below the annual 164
Envlron. Scl. Technol., Vol. 17, No. 3, 1983
National Ambient Air Quality Standard (NAAQS) of 100 pg/m3 (0.05 ppm), it is now well documented that indoor NO2 concentrations often exceed ambient concentrations when gas-burning appliances are used (1-7). Cooking with gas is identified as the principal source for high indoor concentrations, although gas hot water heaters, gas clothes driers, and gas and kerosene space heaters may contribute to elevated indoor levels. When ambient levels and airexchange rates are low, the indoor long-term concentrations can be 5 times higher than the outdoor concentrations. The short-term 5-min to 1-h concentrations can exceed 1000 pg/m3 (0.5 ppm) (8,9).Concentrations this high are rarely observed in ambient air. In 1977, only ten locations reported days where the short-term peak (1h) exceeded 500 pg/m3. Six of these locations were in southern California (10). Some recent epidemiologic studies indicate the possibility of health effects presumably associated with NO2 exposure. A British study by Melia et al. examined 1810 children, 5-11 years old, living in gas-cooking homes, and 3017 children living in electric-cooking homes (11). Although the relative rates varied between boys and girls and among age groups, a higher prevalence of respiratory symptoms and disease was noted for the children dwelling in gas-cooking homes. Keller et al. (12)reported no difference in respiratory symptoms between household groups living in gas- and electric-cooking homes. This U.S. study has been criticized as being insensitive because of the small number of subjects (ca. 600), which were not age stratified in the analysis. In another U.S.study (8) involving some 8000 children 6-10 years old, residing in six cities, respiratory diseases before age 2 and lower pulmonary functions were associated with the presence of gas stoves. While the data analysis controlled for social status and parental smoking, boys and girls were not treated sepa-
00~13-936X/83/0917-0164$01.50/0 0 1983 American Chemical Society
rately in the analysis. The findings of impaired lung functions for the children living in homes with gas stoves was noted for every city; however, the medical significance is not yet clear. In a recent study of 708 nonsmoking adults Comstock et al. (13) found both increased symptoms of respiratory illness and decreased lung function among individuals from households with gas cooking fuel compared to individuals from electric-cooking households. These effects were present after adjusting for sex, age, and several variables associated with social class. All of these reports of adverse health effects associated with gas stoves are presumed to be related to elevated short-term NO2 concentrations. Effects of both single and repeated exposure to short-term peaks have been reported for a variety of animal and human responses (1). A cooperative research program between the University of Wisconsin at Madison and Harvard School of Public Health has been conducted to improve estimates of exposure to NO2 for children participating in a prospective epidemiologic study (14). As part of this cooperative program nitrogen dioxide concentrations were monitored inside and outside 137 homes in Portage, WI. Homes with gas- and electric-cookingstoves were repeatedly monitored for 1-week intervals over a 1-year period by using passive diffusion samples developed by Palmes et al. (15). The objectives of this study were to characterize spatial and temporal variation of NO2 concentrations between and within homes and to develop a model to predict NO2 exposure at home by using descriptive variables obtained from a health survey as well as ambient NO2 levels.
Table I. Sampling Summary stove type
sample weeksa by period: 07/01/80-08/27/80 08/28/80-09/30/80 10/01/80-11/02/80 11/03/80-12/31/80 01/01/81-02/14/81 02/15/81-03/31/81 04/01/81-05/13/81 05/14/81-06/30/81
(16).
Quality assurance procedures included two blanks and at least one replicate sample for every 18 samples, and analysis of unknowns prepared by an independent laboratory. Our initial determination of laboratory performance showed excellent agreement (within 2%) between the Wisconsin and Harvard laboratories. The Palmes diffusion tubes have been examined by Warren Springs Laboratories (17)and the National Bureau of Standards (18). These laboratories reported similar sensitivity of the present configuration of the diffusion tubes as 1150 (pg/m3) h q d an accuracy of within 10%.
23 21 20 23 22 22 23 20 174 25 4
total homes dropouts a
31 32 31 30 29 28 29 29 240 36 3
72 76 72 76 65 72 66 67 568
76 3
Times three tubes at each location.
ELEC-EEDROOII ELEC-KIlCHEN
.
A
4
GUS-BEDROOI
.ORS-KIlCHEN
0
Procedures Participants were selected from a list of families living in Columbia county around Portage, WI, whose elementary-school-aged children participated in the Harvard Air Pollution/Lung Health Study (24). Letters requesting volunteers were preferentially sent to families with gas cooking. Subsequently, we identified the homes that used natural gas and bottled liquid propane as cooking fuel. At least three diffusion tubes were installed in each home. A kitchen monitor was placed on a wall between 4 and 6 feet above the floor and no closer than 10 feet to the stove. A bedroom sampler was similarly placed on a wall away from corners, windows, and forced air vents, in the bedroom of a child. Outdoor monitors were 4-6 feet above the ground on the north or shady side of the house. In an initial visit volunteers were instructed on how the tubes worked, and suitable sampling locations were selected. In the subsequent sampling intervals tubes were mailed with return envelopes. The participating families were instructed to attach the diffusion tubes to the proper locations, uncap them, note the time and date, recap them after 7 days, record the time and date, and return them by postal service to o w staff at the University of Wisconsin at Madison. Analysis was performed at the Wisconsin State Laboratory of Hygiene following a procedure developed by Palmes et al. (15)and modified by Wolfson
natural liquid gas propane
electric
50
100
NO2 C O N C E N T R A T I O N
150
lug/m31
Figure 1. Cumulative frequency distributions of NO2 concentrations by location and type of cooking fuel.
The sampling protocol required homes to be tested for a week-long (ca. 168 h) period twice per season for a total of 8 sample weeks per home. Because of travel and installation times, groups of approximately 20 homes were sampled each week on a 6-week rotating basis. The six groups of homes remained relatively stable throughout the study.
Results A summary of sample collection is presented in Table I. A small number of observations were lost due to improper capping or recapping in the field or the normal laboratory errors. These losses were not related to stove type or time of sampling. Also, three to four homes of each stove-type dropped out of the study during the sampling year. The number of homes sampled during each time period remained stable over the 1-year period reported. Analysis of replicate pairs indicated a high degree of precision of measurement throughout the study. The difference between replicates was less than 8 pg/m3 for 98% of the replicate pairs. Difference scores did not increase with increasing concentration, indicating that the measurement error was additive, not multiplicative. The calculated estimate of precision (the square root of half the variance of the replicate difference scores) was 1.68 pg/m3. There was no trend toward a change of precision over time nor among outdoor, kitchen, and bedroom locations. Cumulative frequency distributions for outdoor observations and indoor observations by stove type are presented in Figure 1. Summary statistics for these distributions are presented in Table 11. First, note the extremely low outdoor concentrations observed. The mean outdoor concentration was 13 pg/m3. Next, note the large Environ. Sci. Technol., Vol. 17, No. 3, 1983
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Table 11. Summary Statistics of NO, Concentrations
electric kitchen bedroom outdoor natural gas kitchen bedroom outdoor LP gas kitchen bedroom outdoor
mean,
sd
N
m3
m
174 172 173
8.4 6.9 12.8
4.7 4.8 5.6
/a/
mean geoI/Oa metric differmean, ence, Pg/ P€
