- Email: [email protected]
On fitting the generalized λ-distribution to air pollution data
1615
DiSCUSSiOllS
conclusions in the paper and include them here only for illustrative purposes), but our conclusion still stands that the data presentgd clearly indicate that the Midwest is the primary source of Se in the Northeast. Note added to pro08 It has been brought to our attention that the 4.9 ngm-3 Se concentration reported for Deep Creek Lake was incorrect in the reference used (Lewis and Stevens, 1987). The correct value is 2.5 ngmm3 (Vossler et al., 1989) This in no way effects the conclusions of our paper as it was not used in the exponential least-squares due to its location. The correct concentration, in fact, is more in line with other measurements in the Midwest or near its eastern boundary, and gives further support fat the noted uniformity of high Se concentrations within the Midwest. DISTANCE
FROM POINT B (km1
1. Average Se concentration as a function of distance from Union County, KY (Point B, Fig. 1 of our paper). The boundary between the Midwest and Northeast has been set at 900 km (an arc approximately passing through Mayville, NY). Selenium concentration west of this boundary has been assigned to Midwest sources (shaded area), east of this boundary the Midwest Se is shown decreasing exponentially with a D,,, of 310 km as explained in the text. Table 1. Estimated Midwest Se components* for sites in the Northeast Site? K L M N 0 P S T U V W X Y
Se concentration (ng m-“) 2.5 2.2 2.2 1.9 1.8 1.6 1.5 1.6 1.6 1.3 1.37 0.76 0.45 1.0 0.6
Midwest Se (%) D,,r=310km D,,,=222 km
lot
1W
96 82 74 78 78 81 69 61 70
90 71 60 62 63 60 54 45 48 43 69 100 45 65 65
l& loot 73 100 Average 82
*The % Midwest Se=(lOO) times Midwest Se based on exponential curve in Fig. 1 divided by the measured Se concentration. t Sites as given in Fig 1 of the paper. $ The Midwest Se contribution set to 100% for this point.
Wadsworth Center for VINCENT A. DUTKIEWICZ Laboratories and Health, LIAQUAT HUSAIN New York State Department of Health, Empire State Plaza, P.O. Box 509, Albany, NY 12201-0509, U.S. A. Department of Environmental Health and Toxicology, School of Public Health, State University of New York at Albany, Empire State Plaza, P.O. Box 509, Albany, NY 12201-0509, USA.
REFERENCES Lewis C. W. and Stevens R. K. (1987) Hybrid receptor modeling. In Chemistry of Acid Rain Sources and Atmospheric Processes. ACS Symposium Series 349. American Chemical Society, Washington, DC. Rahn K. A. and Lowenthal D. H. (1985) Pollution aerosols in the Northeast: Northeastern-Midwestern contributions. Science 22& 275-284. Vossler T. L., Lewis C. W., Stevens R. K., Gordon G. E. and Tuncel S. G. (1989) Composition and origin of summertime air pollutants at Deep Creek Lake, Maryland. Atmospheric Environment 23, 1535-1547.
ON FITTING THE GENERALIZED I-DISTRIBUTION TO AIR POLLUTION DATA* Theimportance of the problem of precise estimation of air
While it is not clear yet whether the value of D,,, obtained by the fit to the Se data in Figure 2 of the paper (310 km) was biased by Northeast Se, this should represent a maximum value. As more recent Se data over a wider range of sites become available a better estimate of D,,, may be obtained and some of the finer detail of Se transport, such as a latitudinal variation, might emerge. The Midwest Se component at-Narragansett in Table 1 is 73 % and 45 % for D,,, of 310 and 222 km. resoectivelv. Rahn and Lowenthal (1985) obtained 50 % from their mu]&element tracer system, however, both values lead to a Midwest component of 100 % at Underhill where they obtained only 65 %. We again caution that generalized quantitative estimates are subject to uncertainties in the data at this time (for this reason we were conservative and avoided such
(ptality distributions is implied by the necessity to estimate accurately extreme values for regulatory purposes. The historical trend seems to be from the use of simpler distributions such as lognormal to morecomplex and flexible distributions such as Gamma, Beta and Weibull. The author suggests an application of the Generalized Lambda Distribution (GLD) which due to its four parameters is expected to be most flexible and to offer best fitting potential because it also covers among others lognormal and Weibull models. The author performed fitting of the GLD and lognormal distributions to a couple of data sets describing empirical SO, and smoke distributions in the Ankara urban ama.
*Okur M. C. (1988)Atmospheric Envtronment Z&2569-2572.
1616
Discussions
of tit between the empirical and theoretical distributions was evaluated using two criteria: KolmogorovSmimov statistic (KS) and the sum of &solute di&ences (AD). Unfortunately the numerical results of fitting are rather disappointing despite the statement by the author that “the overall performance of the two models appears to be close in terms of the goodness-of-fit measures KS and AD”. Goodness
(i) KS values for smoke Set 1 are 0.049 for GLD and 0.39 for lognormal model. This is a vast difference which is completely out of line with other data sets and can be explained only as a typographical error. (ii) KS and AD values for the second data set are always higher for GLD than lognormal m&l, sometimes they are almost twice as large. This would indicate that the lognormal distribution yields much better goodness of fit than GLD (barring the computational errors). However this fact contradicts the logical expectation that GLD should perform better because it is more general and hence more flexible. (iii) The apparent contradiction described in (ii) above is probably the result of different methods used for fitting the two distributions: GLD was fitted using least squares method and lognonnal distribution was fitted using maximum likelihood. Goodness of fit was evaluated using KS statistic but neither of these methods can be expected to have an explicit or implicit effect on decreasing KS distribution distance.
In fact, to draw attention to this model was one of the main objectives of my paper. Ege University, Faculty of Engineering, 35 1Cl0 Bornooa, Izmir,
MEHMETC. OKUR
Turkey
REFERENCES Okur M. C. (1988) A Monte Carlo evaluation of the methods for estimating the parameters of the generahned lambda distribution. In Proceedings of COMPSTAT 1988. Physica-Vetlag, Heidelberg.
AIR POLLUTION AND RURAL BIOMASS FUELS IN DEVELOPING COUNTRIES A PILOT VILLAGE STUDY IN INDIA AND IMPLICATIONS FOR RESEARCH AND POLICY*
It is difficult to explain why such a large difference should exist in BaP numbers in the two studies (Smith et al., 1983 It would be most interesting to perform the parameter and my study) when source condition, sampling methodolestimation for both models using the nonlinear method of KS ogy, TSP sampling protocol and methodology and cook’s minimization. Only this method can really guarantee best fit exposure to TSP were almost identical (Tablo 1). It seems in terms of Kolmogorov-Smimov distribution distance, used more likely that the reason is systematic errors in the BaP in this paper, and hence it can provide a proper assessment of analysis and a detailed description of the analysis and the fitting potential of both distributions. Unfortunately it is calculations by Dr Smith co-authored by Dr A. L. Aggarwal, a well known fact that fitting empirical air quality data by would have been useful. minimizing KS distance is numerically very complicated and The references cited in Smith’s letter were not included in computer power intensive. However the latest APL software my original letter because the combustion mechanisms in for fitting the air quality distribution data which was develthese were very different; high efficiency combustion (U.S. oped at University of Calgary can handle this problem well and European woodstoves characterized by closed comand attempts are being made to evaluate the full potential of bustion zone, controlled air/fuel ratio with primary and GLD using this method. secondary air) vs incomplete combustion (simple open fires in my study and references). The references cited by Smith do not represent combustion conditions in Indian rural cookM. NOSAL stoves and are therefore irrelevant. For example, Smith has Department of Mathematics and Statistics, The Unioersity of Calgary, cited the study (Mast et al., 1984)in which fuel (crop residues) Calgary, Alberta, burnt in an experimental burn tower at the rate of 4 Ibs per Canada 72N lN4 min whereas in a chula (Indian cookstove) it takes 1 h to burn this amount of fuel. Smith’s statement that BaP is not a good indicator of total mutagenicity seems contradictory to his previous statement (1985) where he described how cooking kills in developing countries. It seems that only a well designed environmental AUTHOR’S REPLY epidemiological study can answer the question of health effect of biomass smoke and therefore, presently they are uncertain. BaP’s role as a toxic chemical is adequately I would like to thank Mr Nosal for pointing out the documented. Thyssen et al. (1981) provides evidence of a typographical error in Table 2 which should be corrected as dose-response relationship between inhaled BaP and respir0.039. Although the KS and AD values in Tabk 2 are atory tract tumors in hamsters. ATSDR (1987) has concluded somewhat disappointing, the submquent results demonstrate that BaP can be expected to be carcinogenic in humans by all that the GLD performs far better than the lognormal. So, routes of exposure. Further, scientists from Lawrence Be“the logical expectntion that the GLD should perform bctrkeky Laboratory have indicated BaP’s role in the develter” has clearly been fulfiled in this case. As was stressed in opmestt ofbreast cancer (Journal of Air PolhMon and Control the paper, the measures like KS and AD could be midaading Association July, 1988). in judging the overall fitting performasxce of a probability model. Therefore, it would be better to be on the safe side and PREMLATAMENON Hawaii State Dept. of Health, not to jump to hasty conclusions such as “. . . yields much Hazard Evaluation and Emergency Response, better goodness of fit than .“. 1250 Punchbowl Street, Room # 122, I would be surprkd if other parmneter estimation methHonolulu. HI 96813, U.S.A. ods changed the situation drastically. Because, both Least Squares and Maximum Likelihood are the best available methods for the GLD and lognormal distributions (Okur, *Menon P. and Smith K. R. (1989) Ahnospheric Enuiron1988). However, I am pleased to learn that the full potential ment 23,701-109. of the GLD is being investigated at the University ofcalgary.
1617
Discussions Table 1. Comparison between different parameters in the two studies Menon (1988)
Smith et al. (1983)
Parameters
Gujarat, India Simple U-shaped Mixture of wood and crop residues 1.9 kgh-’ 33 years 46 m3 Cook’s exposure Pump (2-3 Lmin-‘) Glass fiber Half the cooking period7
Location Combustor Fuel type Burn rate Cook’s age Kitchen volume Sampling method Sampler Filter Sampling duration TSP (cont.) Sample size Bap (cont.) Ratio of BaP to TSP Sample size
Entire cookin&eriod/45 Mean: 6.4 mg me3 Range: 1.1-22.5 45 Mean: 4100 ngme3 Range: 62-13,900 Mean: 1000 p’gg-’ 45
Bhopal and Pondicherry, India Simple U-shaped Mixture of wood, dung and crop residues 2.0kgh-’ 30 years 35 m3 Cook’s exposure Pump (2-3 dmin-‘) Glass fiber Entire cooking period/2 h (whichever was lower)
mint Mean: 5.0 mgmm3 Range: 1.0-13.0 129 Mean: 164 ngm-’ Range: O-565 Mean: 122 pgg-’ 16
tSmith et al. have mentioned both in their paper.
REFERENCES
Agency for Toxic Substances and Disease Registry (ATSDR) (1987) Toxicological Profile fir Benzo(a)pyrene (Draft). Published by Oak Ridge National Laboratory for ATSDR, U.&P Public Health Service. Mast T. J., Hseih D. P. H. and Seiber J. N. (1984) Mutagenicity and chemical characterization of organic constituents in rice straw smoke particulate matter. Enuir. Sci. Technol. 18, 338-348. Smith K. R. (1985) How cooking kills in the developing countries. The Asian Wall Street Journal 1 July 1985. Thyssen J., Althoff J., Kimmerle G. and Mohr U. (1981) Inhalation studies with benzo(a)pyrene in Syrian golden hamsters. .I. Natl. Cancer Inst. 66, 575-577.
REPLY TO FURTHER
23:7-M
East-West Center, Honolulu, U.S.A.
KIRK
R. SMITH
REFERENCES World Health Organization (WHO) (1987) Indoor air pollution study, Maragua area, Kenya. WHO/PEP/87.1, WHO, Geneva. WHO (1988) Indoor air quality in the Basse Area, The Gambia. WHO/PEP/88.3, WHO, Geneva.
DISCUSSION
I am sorry that I did not make my point more clearly. It was simply that the air emission factors and ratios for BaP and other pollutants vary over a large range even under the semicontrolled combustion conditions in which most wood smoke studies have been done. Although it might be argued that, even though built in different places and operated by different people, simple open-combustion cookstoves in the field maintain more uniform combustion conditions than metal wood-burning stoves, it nevertheless seems reasonable to believe that fuel types vary more widely. Thus, although it may well be that BaP/TSP ratios in cookstove smoke are often or even usually lower that those we found, there does not seem to be any evidence in the literature today, let alone 6 years ago when the paper was written, indicating that our values were outside some expected range. Because so little work has been done, more research will help. Indeed, two recent studies in Africa found ratios of BaP/TSP in woodsmoke from cookfires to be -50 pgg- I, but apparently averaging less than 100 pgg-’ (WHO, 1987, 1988). These data mc& closely resemble Dr Menon’s thesis results than those of our original study. A more general comment also might be appropriate. Our pilot study, done in 1981, was the first to quantify personal
AE
exposures received by village women in India, but had many limitations. It should not be surprising fhat later studies would result in refinements of the data Indeed, to do so is precisely why we recruited Dr Menon and funded the research that has led to her excellent dissertation.
A LEAF CHAMBER FOR MEASURING THE UPTAKE OF POLLUTANT GASES AT LOW CONCENTRATIONS BY LEAVES, TRANSPIRATION AND CARBON DIOXIDE ASSIMILATION * Theauthors have presented a sound summary of the design and performance of their leaf chair&r for measuring leaf uptake of pollutant gases at low concentrations. A great deal of thought and effort has gone into their design. Given the importance of controlling leaf and chamber temperature, however, it was most interesting that a temperature controlled water jacket was used as the means of temperature control within the leaf chamber. From our experience with leaf chambers in both the laboratory and the field, we have not found the heat exchange performance of a water jacket for chamber temperature control to be very satisfactory. Our
*van Hove L. W. A., Tonk W. J. M., Pieters G. A., Adema E. H. and Vredenberg W. J. (1988) Atmospheric Environment 22,2515-2523.
1618
Discussions
approach has been to use a thermoelectric heat exchanger (Peltier modules) with Teflon coated aluminum fins within the Teflon coated leaf chamber. Water condensation on the heat exchange fins within the leaf chamber was prevented by keeping the fin temperature, at the coldest point, above the dew point. Despite the presence of heat exchange fins, wind speed within theleafchamber was controllable up to 2 m s- ‘. Leaf temperature could also be controlled within the chamber by using a leaf thermocouple to measure leaf temperature and using this signal to alter the chamber air temperature to achieve the desired leaf temperature. The water film problem encountered by the authors is interesting. This may be partially due to their technique of humidity control which is not explained in the paper. Humidity control of the leaf chamber inlet air using the technique of permeation distillation should help minimize this problem. The authors are to be congratulated for a good piece of work. ALLY H. LEGGE
The University oJ Calgary, 2500 Unioersity Drioe N. IV., Calgary, Alberta, Canada l2N lN4
AUTHORS
REPLY
The problems we encountered with NH, and SO, adsorption on the internal surfaces of the leaf chamber appeared to be directly related to the humidity of the air inside the leaf chamber and were not caused by the technique with which a specific air humidity in the air was generated (explained in a previous paper van Hove et al., 1987). There are strong indications that ‘water’ plays an important role in the adsorption of these. and other soluble gases on solid surfaces. It is assumed that this ‘water’ is adsorbed by any surface, resulting in the formation of a thin water layer or water film at higher relative air humidities (Adema et al., 1986). The water film phenomenon also sets a limit to the way, in which temperature of the air within the leaf chamber is controlled. In order to minimize fluctuations in the concentrations of pollutant gases it is of particular importance, that there are no local differences in surface temperature, nor fluctuations in air temperature inside the leaf chamber. Only then, in an undisturbed situation, the uptake of pollutant gases by leaves can be measured with great accuracy. In our design a water
jacket was the best solution meeting these requirements, although a built-in thermoelectric heat exchanger would have been more convenient to regulate air temperature. Other reasons not to use internal heating and cooling elements were, that: (i) in our design any mechanical obstruction would lower the maximum obtainable wind velocity; (ii) internal heating and cooling elements introduce materials with which pollutant gases may react. With regard to Teflon coating we have to remark, that our experiences with this method have not been very satisfactory so far: a complete covering of the internal surfaces, as well as a complete ‘closing’ of the surface pores, were hard to accomplish with this technique. It is obvious, that more research is necessary to find materials or methods of treating surfaces to minimize the adsorption problem. This is not only important with regard to the development of leaf chambers, but also for the development of other devices for measuring and handling pollutant gases, in particular at very low concentrations. At our department research is going on to obtain more fundamental information on the role of water films in the dry deposition of pollutant gases on solid surfaces (Adema et al., 1986). In connection with the developing of new measuring instruments also a modest start has been made with studying the adsorption of low concentrations of pollutant gases by different materials (Sauren et al., 1989). L. W. A. VANHove: Agricultural University, W.J.M.TONK Wageningen, E. H. ADEMA P.O. Box 8129, 6700 EV Wageningen, The Netherlands REFERENCES
Adema E. H., Heeres P. and Hulskotte J. (1986) On the dry deposition of NH,, SO, and NO, on wet surfaces in a small scale windtunnel. In Proceedings 7th Wortd Clean Air Congress 2, 1-8.
Sauren H., van Hove L. W. A., Tonk W. J. M., Jalink H. and Bicanic D. (1989) On the adsorption properties of ammonia. In Monitoring of Gaseous Pollutants by Tunable Diode Lasers (edited by Grisar R., Preier H. and Schmidtke G.). Reidel, Dordrecht. van Hove L. W. A., Koops A. J., Adema E. H., Vredenberg W. J. and Pieters G. A. (1987) Analysis of the uptake of atmospheric ammonia by leaves of Phaseolus vulgaris L. Atmospheric
Environment 21, 1759-1763.
DiSCUSSiOllS
conclusions in the paper and include them here only for illustrative purposes), but our conclusion still stands that the data presentgd clearly indicate that the Midwest is the primary source of Se in the Northeast. Note added to pro08 It has been brought to our attention that the 4.9 ngm-3 Se concentration reported for Deep Creek Lake was incorrect in the reference used (Lewis and Stevens, 1987). The correct value is 2.5 ngmm3 (Vossler et al., 1989) This in no way effects the conclusions of our paper as it was not used in the exponential least-squares due to its location. The correct concentration, in fact, is more in line with other measurements in the Midwest or near its eastern boundary, and gives further support fat the noted uniformity of high Se concentrations within the Midwest. DISTANCE
FROM POINT B (km1
1. Average Se concentration as a function of distance from Union County, KY (Point B, Fig. 1 of our paper). The boundary between the Midwest and Northeast has been set at 900 km (an arc approximately passing through Mayville, NY). Selenium concentration west of this boundary has been assigned to Midwest sources (shaded area), east of this boundary the Midwest Se is shown decreasing exponentially with a D,,, of 310 km as explained in the text. Table 1. Estimated Midwest Se components* for sites in the Northeast Site? K L M N 0 P S T U V W X Y
Se concentration (ng m-“) 2.5 2.2 2.2 1.9 1.8 1.6 1.5 1.6 1.6 1.3 1.37 0.76 0.45 1.0 0.6
Midwest Se (%) D,,r=310km D,,,=222 km
lot
1W
96 82 74 78 78 81 69 61 70
90 71 60 62 63 60 54 45 48 43 69 100 45 65 65
l& loot 73 100 Average 82
*The % Midwest Se=(lOO) times Midwest Se based on exponential curve in Fig. 1 divided by the measured Se concentration. t Sites as given in Fig 1 of the paper. $ The Midwest Se contribution set to 100% for this point.
Wadsworth Center for VINCENT A. DUTKIEWICZ Laboratories and Health, LIAQUAT HUSAIN New York State Department of Health, Empire State Plaza, P.O. Box 509, Albany, NY 12201-0509, U.S. A. Department of Environmental Health and Toxicology, School of Public Health, State University of New York at Albany, Empire State Plaza, P.O. Box 509, Albany, NY 12201-0509, USA.
REFERENCES Lewis C. W. and Stevens R. K. (1987) Hybrid receptor modeling. In Chemistry of Acid Rain Sources and Atmospheric Processes. ACS Symposium Series 349. American Chemical Society, Washington, DC. Rahn K. A. and Lowenthal D. H. (1985) Pollution aerosols in the Northeast: Northeastern-Midwestern contributions. Science 22& 275-284. Vossler T. L., Lewis C. W., Stevens R. K., Gordon G. E. and Tuncel S. G. (1989) Composition and origin of summertime air pollutants at Deep Creek Lake, Maryland. Atmospheric Environment 23, 1535-1547.
ON FITTING THE GENERALIZED I-DISTRIBUTION TO AIR POLLUTION DATA* Theimportance of the problem of precise estimation of air
While it is not clear yet whether the value of D,,, obtained by the fit to the Se data in Figure 2 of the paper (310 km) was biased by Northeast Se, this should represent a maximum value. As more recent Se data over a wider range of sites become available a better estimate of D,,, may be obtained and some of the finer detail of Se transport, such as a latitudinal variation, might emerge. The Midwest Se component at-Narragansett in Table 1 is 73 % and 45 % for D,,, of 310 and 222 km. resoectivelv. Rahn and Lowenthal (1985) obtained 50 % from their mu]&element tracer system, however, both values lead to a Midwest component of 100 % at Underhill where they obtained only 65 %. We again caution that generalized quantitative estimates are subject to uncertainties in the data at this time (for this reason we were conservative and avoided such
(ptality distributions is implied by the necessity to estimate accurately extreme values for regulatory purposes. The historical trend seems to be from the use of simpler distributions such as lognormal to morecomplex and flexible distributions such as Gamma, Beta and Weibull. The author suggests an application of the Generalized Lambda Distribution (GLD) which due to its four parameters is expected to be most flexible and to offer best fitting potential because it also covers among others lognormal and Weibull models. The author performed fitting of the GLD and lognormal distributions to a couple of data sets describing empirical SO, and smoke distributions in the Ankara urban ama.
*Okur M. C. (1988)Atmospheric Envtronment Z&2569-2572.
1616
Discussions
of tit between the empirical and theoretical distributions was evaluated using two criteria: KolmogorovSmimov statistic (KS) and the sum of &solute di&ences (AD). Unfortunately the numerical results of fitting are rather disappointing despite the statement by the author that “the overall performance of the two models appears to be close in terms of the goodness-of-fit measures KS and AD”. Goodness
(i) KS values for smoke Set 1 are 0.049 for GLD and 0.39 for lognormal model. This is a vast difference which is completely out of line with other data sets and can be explained only as a typographical error. (ii) KS and AD values for the second data set are always higher for GLD than lognormal m&l, sometimes they are almost twice as large. This would indicate that the lognormal distribution yields much better goodness of fit than GLD (barring the computational errors). However this fact contradicts the logical expectation that GLD should perform better because it is more general and hence more flexible. (iii) The apparent contradiction described in (ii) above is probably the result of different methods used for fitting the two distributions: GLD was fitted using least squares method and lognonnal distribution was fitted using maximum likelihood. Goodness of fit was evaluated using KS statistic but neither of these methods can be expected to have an explicit or implicit effect on decreasing KS distribution distance.
In fact, to draw attention to this model was one of the main objectives of my paper. Ege University, Faculty of Engineering, 35 1Cl0 Bornooa, Izmir,
MEHMETC. OKUR
Turkey
REFERENCES Okur M. C. (1988) A Monte Carlo evaluation of the methods for estimating the parameters of the generahned lambda distribution. In Proceedings of COMPSTAT 1988. Physica-Vetlag, Heidelberg.
AIR POLLUTION AND RURAL BIOMASS FUELS IN DEVELOPING COUNTRIES A PILOT VILLAGE STUDY IN INDIA AND IMPLICATIONS FOR RESEARCH AND POLICY*
It is difficult to explain why such a large difference should exist in BaP numbers in the two studies (Smith et al., 1983 It would be most interesting to perform the parameter and my study) when source condition, sampling methodolestimation for both models using the nonlinear method of KS ogy, TSP sampling protocol and methodology and cook’s minimization. Only this method can really guarantee best fit exposure to TSP were almost identical (Tablo 1). It seems in terms of Kolmogorov-Smimov distribution distance, used more likely that the reason is systematic errors in the BaP in this paper, and hence it can provide a proper assessment of analysis and a detailed description of the analysis and the fitting potential of both distributions. Unfortunately it is calculations by Dr Smith co-authored by Dr A. L. Aggarwal, a well known fact that fitting empirical air quality data by would have been useful. minimizing KS distance is numerically very complicated and The references cited in Smith’s letter were not included in computer power intensive. However the latest APL software my original letter because the combustion mechanisms in for fitting the air quality distribution data which was develthese were very different; high efficiency combustion (U.S. oped at University of Calgary can handle this problem well and European woodstoves characterized by closed comand attempts are being made to evaluate the full potential of bustion zone, controlled air/fuel ratio with primary and GLD using this method. secondary air) vs incomplete combustion (simple open fires in my study and references). The references cited by Smith do not represent combustion conditions in Indian rural cookM. NOSAL stoves and are therefore irrelevant. For example, Smith has Department of Mathematics and Statistics, The Unioersity of Calgary, cited the study (Mast et al., 1984)in which fuel (crop residues) Calgary, Alberta, burnt in an experimental burn tower at the rate of 4 Ibs per Canada 72N lN4 min whereas in a chula (Indian cookstove) it takes 1 h to burn this amount of fuel. Smith’s statement that BaP is not a good indicator of total mutagenicity seems contradictory to his previous statement (1985) where he described how cooking kills in developing countries. It seems that only a well designed environmental AUTHOR’S REPLY epidemiological study can answer the question of health effect of biomass smoke and therefore, presently they are uncertain. BaP’s role as a toxic chemical is adequately I would like to thank Mr Nosal for pointing out the documented. Thyssen et al. (1981) provides evidence of a typographical error in Table 2 which should be corrected as dose-response relationship between inhaled BaP and respir0.039. Although the KS and AD values in Tabk 2 are atory tract tumors in hamsters. ATSDR (1987) has concluded somewhat disappointing, the submquent results demonstrate that BaP can be expected to be carcinogenic in humans by all that the GLD performs far better than the lognormal. So, routes of exposure. Further, scientists from Lawrence Be“the logical expectntion that the GLD should perform bctrkeky Laboratory have indicated BaP’s role in the develter” has clearly been fulfiled in this case. As was stressed in opmestt ofbreast cancer (Journal of Air PolhMon and Control the paper, the measures like KS and AD could be midaading Association July, 1988). in judging the overall fitting performasxce of a probability model. Therefore, it would be better to be on the safe side and PREMLATAMENON Hawaii State Dept. of Health, not to jump to hasty conclusions such as “. . . yields much Hazard Evaluation and Emergency Response, better goodness of fit than .“. 1250 Punchbowl Street, Room # 122, I would be surprkd if other parmneter estimation methHonolulu. HI 96813, U.S.A. ods changed the situation drastically. Because, both Least Squares and Maximum Likelihood are the best available methods for the GLD and lognormal distributions (Okur, *Menon P. and Smith K. R. (1989) Ahnospheric Enuiron1988). However, I am pleased to learn that the full potential ment 23,701-109. of the GLD is being investigated at the University ofcalgary.
1617
Discussions Table 1. Comparison between different parameters in the two studies Menon (1988)
Smith et al. (1983)
Parameters
Gujarat, India Simple U-shaped Mixture of wood and crop residues 1.9 kgh-’ 33 years 46 m3 Cook’s exposure Pump (2-3 Lmin-‘) Glass fiber Half the cooking period7
Location Combustor Fuel type Burn rate Cook’s age Kitchen volume Sampling method Sampler Filter Sampling duration TSP (cont.) Sample size Bap (cont.) Ratio of BaP to TSP Sample size
Entire cookin&eriod/45 Mean: 6.4 mg me3 Range: 1.1-22.5 45 Mean: 4100 ngme3 Range: 62-13,900 Mean: 1000 p’gg-’ 45
Bhopal and Pondicherry, India Simple U-shaped Mixture of wood, dung and crop residues 2.0kgh-’ 30 years 35 m3 Cook’s exposure Pump (2-3 dmin-‘) Glass fiber Entire cooking period/2 h (whichever was lower)
mint Mean: 5.0 mgmm3 Range: 1.0-13.0 129 Mean: 164 ngm-’ Range: O-565 Mean: 122 pgg-’ 16
tSmith et al. have mentioned both in their paper.
REFERENCES
Agency for Toxic Substances and Disease Registry (ATSDR) (1987) Toxicological Profile fir Benzo(a)pyrene (Draft). Published by Oak Ridge National Laboratory for ATSDR, U.&P Public Health Service. Mast T. J., Hseih D. P. H. and Seiber J. N. (1984) Mutagenicity and chemical characterization of organic constituents in rice straw smoke particulate matter. Enuir. Sci. Technol. 18, 338-348. Smith K. R. (1985) How cooking kills in the developing countries. The Asian Wall Street Journal 1 July 1985. Thyssen J., Althoff J., Kimmerle G. and Mohr U. (1981) Inhalation studies with benzo(a)pyrene in Syrian golden hamsters. .I. Natl. Cancer Inst. 66, 575-577.
REPLY TO FURTHER
23:7-M
East-West Center, Honolulu, U.S.A.
KIRK
R. SMITH
REFERENCES World Health Organization (WHO) (1987) Indoor air pollution study, Maragua area, Kenya. WHO/PEP/87.1, WHO, Geneva. WHO (1988) Indoor air quality in the Basse Area, The Gambia. WHO/PEP/88.3, WHO, Geneva.
DISCUSSION
I am sorry that I did not make my point more clearly. It was simply that the air emission factors and ratios for BaP and other pollutants vary over a large range even under the semicontrolled combustion conditions in which most wood smoke studies have been done. Although it might be argued that, even though built in different places and operated by different people, simple open-combustion cookstoves in the field maintain more uniform combustion conditions than metal wood-burning stoves, it nevertheless seems reasonable to believe that fuel types vary more widely. Thus, although it may well be that BaP/TSP ratios in cookstove smoke are often or even usually lower that those we found, there does not seem to be any evidence in the literature today, let alone 6 years ago when the paper was written, indicating that our values were outside some expected range. Because so little work has been done, more research will help. Indeed, two recent studies in Africa found ratios of BaP/TSP in woodsmoke from cookfires to be -50 pgg- I, but apparently averaging less than 100 pgg-’ (WHO, 1987, 1988). These data mc& closely resemble Dr Menon’s thesis results than those of our original study. A more general comment also might be appropriate. Our pilot study, done in 1981, was the first to quantify personal
AE
exposures received by village women in India, but had many limitations. It should not be surprising fhat later studies would result in refinements of the data Indeed, to do so is precisely why we recruited Dr Menon and funded the research that has led to her excellent dissertation.
A LEAF CHAMBER FOR MEASURING THE UPTAKE OF POLLUTANT GASES AT LOW CONCENTRATIONS BY LEAVES, TRANSPIRATION AND CARBON DIOXIDE ASSIMILATION * Theauthors have presented a sound summary of the design and performance of their leaf chair&r for measuring leaf uptake of pollutant gases at low concentrations. A great deal of thought and effort has gone into their design. Given the importance of controlling leaf and chamber temperature, however, it was most interesting that a temperature controlled water jacket was used as the means of temperature control within the leaf chamber. From our experience with leaf chambers in both the laboratory and the field, we have not found the heat exchange performance of a water jacket for chamber temperature control to be very satisfactory. Our
*van Hove L. W. A., Tonk W. J. M., Pieters G. A., Adema E. H. and Vredenberg W. J. (1988) Atmospheric Environment 22,2515-2523.
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Discussions
approach has been to use a thermoelectric heat exchanger (Peltier modules) with Teflon coated aluminum fins within the Teflon coated leaf chamber. Water condensation on the heat exchange fins within the leaf chamber was prevented by keeping the fin temperature, at the coldest point, above the dew point. Despite the presence of heat exchange fins, wind speed within theleafchamber was controllable up to 2 m s- ‘. Leaf temperature could also be controlled within the chamber by using a leaf thermocouple to measure leaf temperature and using this signal to alter the chamber air temperature to achieve the desired leaf temperature. The water film problem encountered by the authors is interesting. This may be partially due to their technique of humidity control which is not explained in the paper. Humidity control of the leaf chamber inlet air using the technique of permeation distillation should help minimize this problem. The authors are to be congratulated for a good piece of work. ALLY H. LEGGE
The University oJ Calgary, 2500 Unioersity Drioe N. IV., Calgary, Alberta, Canada l2N lN4
AUTHORS
REPLY
The problems we encountered with NH, and SO, adsorption on the internal surfaces of the leaf chamber appeared to be directly related to the humidity of the air inside the leaf chamber and were not caused by the technique with which a specific air humidity in the air was generated (explained in a previous paper van Hove et al., 1987). There are strong indications that ‘water’ plays an important role in the adsorption of these. and other soluble gases on solid surfaces. It is assumed that this ‘water’ is adsorbed by any surface, resulting in the formation of a thin water layer or water film at higher relative air humidities (Adema et al., 1986). The water film phenomenon also sets a limit to the way, in which temperature of the air within the leaf chamber is controlled. In order to minimize fluctuations in the concentrations of pollutant gases it is of particular importance, that there are no local differences in surface temperature, nor fluctuations in air temperature inside the leaf chamber. Only then, in an undisturbed situation, the uptake of pollutant gases by leaves can be measured with great accuracy. In our design a water
jacket was the best solution meeting these requirements, although a built-in thermoelectric heat exchanger would have been more convenient to regulate air temperature. Other reasons not to use internal heating and cooling elements were, that: (i) in our design any mechanical obstruction would lower the maximum obtainable wind velocity; (ii) internal heating and cooling elements introduce materials with which pollutant gases may react. With regard to Teflon coating we have to remark, that our experiences with this method have not been very satisfactory so far: a complete covering of the internal surfaces, as well as a complete ‘closing’ of the surface pores, were hard to accomplish with this technique. It is obvious, that more research is necessary to find materials or methods of treating surfaces to minimize the adsorption problem. This is not only important with regard to the development of leaf chambers, but also for the development of other devices for measuring and handling pollutant gases, in particular at very low concentrations. At our department research is going on to obtain more fundamental information on the role of water films in the dry deposition of pollutant gases on solid surfaces (Adema et al., 1986). In connection with the developing of new measuring instruments also a modest start has been made with studying the adsorption of low concentrations of pollutant gases by different materials (Sauren et al., 1989). L. W. A. VANHove: Agricultural University, W.J.M.TONK Wageningen, E. H. ADEMA P.O. Box 8129, 6700 EV Wageningen, The Netherlands REFERENCES
Adema E. H., Heeres P. and Hulskotte J. (1986) On the dry deposition of NH,, SO, and NO, on wet surfaces in a small scale windtunnel. In Proceedings 7th Wortd Clean Air Congress 2, 1-8.
Sauren H., van Hove L. W. A., Tonk W. J. M., Jalink H. and Bicanic D. (1989) On the adsorption properties of ammonia. In Monitoring of Gaseous Pollutants by Tunable Diode Lasers (edited by Grisar R., Preier H. and Schmidtke G.). Reidel, Dordrecht. van Hove L. W. A., Koops A. J., Adema E. H., Vredenberg W. J. and Pieters G. A. (1987) Analysis of the uptake of atmospheric ammonia by leaves of Phaseolus vulgaris L. Atmospheric
Environment 21, 1759-1763.