United States Environmental Protection Agency Air and Energy Engineering Research Laboratory Research Triangle Park NC 27711 Research and Development EPA/600/S9-87/005 Apr. 1987 &EPA Project Summary Pollutant Emission Factors for Gas Stoves: A Literature Survey Cliff I. Davidson, John E. Borrazzo, and Chris T. Hendrickson Published emission factors for CO, NO, NO2, NOX have been summarized for gas-fired kitchen stoves. Analysis of variance was then used to investigate the importance of three binary factors: type of combustion, burner position, and method of sampling. The emission factor data were then used to estimate coefficients in various multivariate re- gression models. The influence of gas flow rate on emission factors was in- vestigated separately. The data were also used to investigate the sensitivity of predicted airborne concentrations to uncertainties in emission factors. Final- ly, the data were used to identify critical gaps in understanding emission factors. This Protect Summary was developed by EPA's Air and Energy Engineering Research Laboratory, Research Triangle Park, NC, to announce key findings of the research project that Is fully docu- mented In a separate report of the same title (see Project Report ordering In- formation at back). The Survey Published emission factors for CO, NO, N02, and NOX for gas-fired kitchen stoves have been summarized. To the extent that data exist, the emission factors have been used in a statistical analysis to investigate the most important factors influencing emissions. First, the data were used to construct normal probability and log probability plots based on the cumulative distribution of the emission factors. Correlation coef- ficients were computed for both types of plots. Results showed that the log prob- ability plot provided a better fit to the CO and NO2 data with reasonably high cor- relation coefficients, suggesting that the emission factors for these pollutants may be approximated by lognormal distribu- tions. Either normal or lognormal distri- butions were satisfactory for NO and NOX. For consistency, the emission fac- tors for all four pollutants were assumed to be distributed lognormally in sub- sequent analysis. Analysis of variance was then used to investigate the importance of three binary factors in explaining the observed vari- ations in emissions: (1) type of combustion (poorly adjusted or well adjusted), (2) burner position (front or rear), and (3) method of sampling (direct or indirect). The results showed that roughly half of the observed variance in log EF (base 10 logarithm of the emission factor) for CO can be explained by noting if the com- bustion is poorly adjusted. For N02, roughly 30% of the variance can be ex- plained by this factor. For NO and NOX, the fraction of variance explained by this factor depends on the subset of the data chosen: fractions ranged from 0.088 to 0.56. Burner position and method of sampling were both relatively unim- portant in explaining the observed vari- ance for any of the four pollutants. The emission factor data were then used to estimate coefficients in various multivariate regression models. The first regression model incorporated several factors: type of combustion, burner posi- tion, method of sampling, the three two- way interactions between these factors, and (M-1) binary factors corresponding to the M stoves for which data were avail- able (M=27, 26, 26, and 8 for CO, NO, N02 and NOX, respectively). Subsequent multivariate regression models were constructed by sequentially eliminating a factor or factors from the previous model. Results of these tests showed that stove differences were significant at the 95% level in explaining the variance in CO, ------- N02, and NOX emission factor. Type of combustion was significant for CO, NO, and N02. Burner position had a smaller but still statistically significant effect in explaining the variance 'in CO and N02 emissions. Similarly, the method of sam- pling had a small but statistically signifi- cant effect for NOX emissions. The influence of gas flow rate on emis- sion factors was investigated separately. Statistical tests were not run for this factor due to both a lack of data and the presence of detailed data from only one study. Results of plotting all of the data for each pollutant on a common graph showed that CO and N02 emissions vary considerably with gas flow rate, while emissions of NO and NOX are less variable. The data were used to investigate the sensitivity of predicted airborne concen- trations to uncertainties in emission factors. The solution of a one-compart- ment mass balance model was used as the predictor of concentration. For the existing distribution of emission factor data, the current uncertainty in CO is responsible for a larger fraction of the variance in predicted concentration than uncertainty in air exchange rate. For NO and NO2, however, the uncertainty in air exchange rate is more important than the emission factor uncertainties. Finally, the data were used to identify critical gaps in understanding emission factors and to suggest future experiments. Overall, it is concluded that the influence of stove design, gas flow rate, and char- acteristics of stove use are key factors which merit further study. C. Davidson, J. Borrazzo, and C. Hendrickson are with Carnegie-Mellon University, Pittsburgh, PA 15213. Jane M. Crum is the EPA Project Officer (see below). The complete report, entitled "Pollutant Emission Factors for Gap Stoves: A Literature Survey," (Order No. PB 87-171 328/AS; Cost: $18.95, subject to change) will be available only from: National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 Telephone: 703-487-4650 The EPA Project Officer can be contacted at: Air and Energy Engineering Research Laboratory Laboratory U.S. Environmental Protection Agency ResearchJriangle Park, NC 27711 United States Environmental Protection Agency Center for Environmental Research Information Cincinnati OH 45268 Official Business Penalty for Private Use $300 EPA/600/S9-87/005 0000329 PS U S ENVIR PROTECTION AGENCY REGION 5 LIBRARY 230 S DEARBORN STREET CHICAGO IL 60604 ------- |