Atmospheric Enrironment Vol. 27A, No. 14. p. 2249. 1993 0004 6981/93 $6.00+0.00 Printed in Great Britain. Pergamon Press Ltd

AUTHORS' REPLY TO R E S P O N S E

Rosebrook and Worm state that the error treatment in Appendix D of Wallace (1987) found correction factors for benzene, ethylbenzene and xylenes that were either extremely large or incalculable. Since these factors were calculated separately for overnight and daytime personal and outdoor air measurements, and also for breath, there were a total of 44 such factors calculated for these aromatics, of which 9 were found to be incalculable. (Six of these occurred during the second season, following the contamination incident in the storage site.) Most of the 35 calculated correction factors were in the range 0.8-0.98 (i.e. the observed 84th percentile value should be multiplied by a number between 0.8 and 0.98 to provide a corrected estimate.

Rosebrook and Worm state that they "'stand by" their contention that levels of benzene reported for N J1 are misleadingly high. However, this appears to be new their earlier comments included no such contention, in their conclusions or elsewhere. Rosebrook and Worm provide no basis for this statement. The mere existence of background contamination on blank cartridges does not imply that reported values will be too high--they could be too high or too low, depending on whether the blanks are over- or under- corrected. The personal air and outdoor air benzene values for NJ 1 appear to be quite similar to measurements by us and others in many cities. For example, the population-weighted personal air geometric mean values for benzene in NJ 1 were l l . 2 p g m 3 in the daytime and 12.5#gin -3 at night. In Baltimore, the corresponding values were 8.4 and 12.3 #gm -3. In Los Angeles during the winter, the values were 15.1 and 13.6 pgm 3 in 1984, and 12.7 and 10.4 pgm -3 in 1987 (Wallace, 1989a). These studies had significantly less background contamination than in NJ1. Similarly, our geo- metric mean levels for benzene in outdoor air in NJ1 were 3.8 pgm 3 at night and 4.1 pgm 3 during the day. Later TEAM studies found benzene levels of ranging between 2.6 and 16.5 #gm 3 in Los Angeles (Wallace, 1989a). Another study using different sampling methodology reports median outdoor rush hour concentrations ranging from 2 to 17 ~g m - 3 in 39 U.S. cities, with a median value of 6 #g m- 3 (Seila, 1987). Twenty-four hour bag samples in California also show median benzene levels that are generally greater than the 4 #gm 3 observed in N J1 (California Air Resources Board Toxic Gases database, 1986-90). We conclude that it is unlikely that our personal air and outdoor air benzene measurements in N J1 are overestimates.

Rosebrook and Worm state that various papers (Wallace, 1989a, b,c, 1990) have discussions based on grand means. All of these papers provide individual data by city. For example, Wallace (1989a) includes three tables and five figures pre- senting personal air, outdoor air and breath values of ben- zene by city, none of which refer to a "grand mean." The last figure (fig. 6) attempts to arrive at estimates of average daily intake of benzene due to different sources. This figure em- ploys estimates of typical levels due to the source for example, it uses the sales-weighted average tar and nicotine cigarette to estimate benzene intake from active smoking. It also employs a value of 6 #gin -3 for a typical outdoor air level, based not only TEAM study measurements but on other measurements such as in Seila 0987). Certainly, even with perfect data, choosing some "typical" or "average" value

from a heterogenous data set is not a well-defined mathematical operation. That is why all these papers in- cluded the data from the individual TEAM cities, so that readers could see the full range and variability of the data.

The population-weighted geometric mean personal expo- sures to benzene were 11 12~gm 3, compared to outdoor values of 3.8-4.1/~gm -3 (table 6 of Wallace et al., 1985). This corresponds to an outdoor air contribution to benzene exposure of about 35%. However, measured personal expo- sures to benzene did not include the contribution of active smoking. When this is considered, the impact of outdoor benzene on exposure for the New Jersey target population drops to about 20-25%, as we stated. Table 9 of Wallace et al. (1985), which contains an estimate of about 53%, refers only to overniyht personal exposures (when the participant was asleep much of the time). Since activities such as driving and smoking increase exposure, and often take place else- where than the home, the daytime outdoor air/personal air ratio will tend to be smaller than the overnight outdoor air/indoor air ratio. We agree with Rosebrook and Worm that outdoor air can have a significant effect on indoor air, and have calculated the magnitude of that effect. For ex- ample, stepwise regressions selected outdoor air benzene as the most significant variable affecting overnight personal (i.e. indoor air) levels of benzene in N J1 (Appendix B of Wallace, 1987). However, in the 1984 Los Angeles data, stepwise regressions selected a smoker in the home as the most significant variable, and outdoor air levels were not signific- ant at the 0.05 level.

REFERENCES

Seila R. L. (1987) 6-9 AM Ambient Air Benzene Concentra- tions in 39 U.S. Cities, 1984-86. In Proc. of the 1987 EPA/APCA Symposium on Measurement of Toxic Air Pollutants, pp. 265-70. Air Pollution Control Assoc., Pittsburgh. APCA VIP-8. EPA 600/9-87-010,

Wallace L. A., Pellizzari E. D., Hartwell T. D., Sparacino C. M., Sheldon U S. and Zelon H. (1985) Personal exposures, indoor-outdoor relationships and breath levels of toxic air pollutants measured for 355 persons in New Jersey. Atmospheric Environment 19, 1651-1661.

Wallace L. A. (1987) The TEAM study: summary and analysis, volume I. EPA 600/6-87/002a, NTIS PB 88- 100060. U.S. EPA, Washington, DC.

Wallace L. A. (1989a)The exposure of the general population to benzene, Cell Biol, Tox. 5, 297-314.

Wallace L. A. (1989b) The total exposure assessment meth- odology (TEAM) study: an analysis of exposures, sources and risks associated with four volatile organic chemicals. 2. Am. Col. Tox. 8, 883-895.

Wallace L. A. (1989e) Major sources of benzene exposure. Envir. Hlth Persp. 82, 165-169.

Wallace L. A. (1990) Major source of exposure to benzene and other volatile organic chemicals. Risk Anal. 10, 59-64.

L. WALLACE T. HARTWELL

and E. PELL1ZZARI

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