Personal monitoring of selected VOCs: the contribution of woodsmoke to exposure
Technical Report No. 8
CSIRO Atmospheric Research, May 2004
ISBN 0 6425 5025 5
About this report
A study of personal exposure to the air toxics benzene, toluene, ethylbenzene and xylene (BTEX), and woodheater usage in Launceston, was conducted over a period of seven days in both March (summer) and June (winter), 2003. The study was conducted using participants from 28 households without woodheaters, 19 households with woodheaters compliant with Australian Standard AS/NZ 4013:1999, and 30 households with non-compliant woodheaters. Personal exposure, outdoor and indoor BTEX concentrations were measured along with some supporting aerosol measurements of particulate matter (as PM10). Study participants documented relevant activities in their personal and household diaries throughout both sampling periods.
The first objective was to develop 'an increased understanding of the relationship between outdoor and indoor woodsmoke and personal exposure to benzene, toluene, ethylbenzene and xylene (BTEX)'. The overall characteristics of the BTEX measurements were that outdoor air always had the lowest concentrations, followed by indoor household concentrations, with the highest concentrations from personal exposure measurements. The difference between indoor concentration and personal exposure concentration was, on average, about two-thirds of the difference between the outdoor and the indoor concentrations. There was a substantial increase in concentration in moving from summer to winter months, with the increases being around a factor of two to three for personal exposure and indoor concentrations, and a factor of three to seven for outdoor concentrations. Similarly, the PM10 aerosol concentrations were much higher in winter than in summer.
Data analysis indicated that woodsmoke contributes to personal exposure to BTEX in Launceston by contributing to the ambient outdoor concentration of BTEX. A comparison of the concentration ratios of BTEX species and PM10 observed in this study and the estimated emission ratios for PM10, benzene, toluene and xylene for Launceston from the National Pollution Inventory gave good agreement between the atmospheric concentration measurements and the National Pollution Inventory. The emissions inventory data indicate that approximately two thirds of the ambient outdoor BTEX species and PM10 concentrations arise from woodheater usage, and these estimates are confirmed by this study. The outdoor BTEX concentration makes a minimum baseline contribution to the BTEX concentrations in indoor air. Indoor sources also contribute to the indoor concentrations. Finally, personal exposure to BTEX species is highly correlated with the participants' indoor household concentration.
The second objective of the study was to determine 'factors that influence personal exposure to BTEX from wood heating, including woodheater type (compliant/non-compliant), firewood type, firewood moisture content, firewood load, loading geometry and airflow settings'. A statistical analysis of the BTEX measurements showed there was no difference between the indoor concentrations of BTEX for the three classes of household types (no woodheater, compliant woodheater and non-compliant woodheater), indicating that in the households sampled in this study, the presence and use of a woodheater within their home had no influence on the BTEX concentration within that home. This conclusion is reinforced by a regression analysis, which showed that there was no significant relationship between BTEX exposure, BTEX indoor concentration, and several variables that are measures of the level of woodheater use within the home. These variables were the amount of time the woodheater was on, number of times the woodheater was refuelled, and number of times that woodsmoke odour was detected. Thus, the domestic use of a woodheater does not directly increase personal exposure to BTEX within the home, but indirectly increases exposure by raising outdoor levels.
The third objective was to determine 'whether ambient monitoring for particles is an accurate reflection of personal exposure to BTEX, by comparison of BTEX personal exposure data with particle monitoring data for NEPM reporting purposes'. Launceston's BTEX levels in outdoor air during summer were very low and were poorly correlated with PM10 concentrations. In winter, there was a positive correlation of r² = 0.76 between benzene in outdoor air and particulate matter (PM10) in outdoor air. A similar correlation was observed between BTEX in outdoor air and PM10 in outdoor air. The sources of BTEX and PM10 are partially common (woodheaters and motor vehicles) and partially separate (other chemical manufacturing for BTEX alone, and paved and unpaved roads for PM10 alone). The correlation between BTEX and PM10 is not necessarily because of the commonality of the sources, but more likely because all of these sources emit into the Launceston airshed, where the pollutants are mixed within the air. BTEX and PM10 levels were dependent on the ventilation rate within the airshed, as a result of prevailing winds - higher ventilation rates resulted in lower pollutant levels and vice versa. A correlation was thus found between BTEX and PM10 levels, but this was mainly due to a combination of co-location of sources and meteorology and, to a lesser extent, by the degree of commonality of their sources.
The study data show that in Launceston, personal exposure to benzene arises from two sources, a baseline or minimum contribution that is present in outside air, plus an additional contribution that arises from indoor sources. The indoor contribution was comparable to the outdoor contribution and was not found to be associated with woodheater use in the household. Typically for benzene, the additional contribution to the personal exposure that arose from indoor sources made a contribution in most cases roughly equal to the outdoor amount, and in one extreme result, the indoor contribution to the personal exposure to benzene was nearly ten times the outdoor amount. Thus, ambient PM10 measurements in Launceston reflect the minimum level of BTEX personal exposure that can occur, but are not in most cases an accurate measure of the actual BTEX personal exposure. This relationship may not be applicable to other cities.
It should be noted that the National Pollutant Inventory for Launceston omits motor vehicles and woodheater usage as sources of ethylbenzene. Study results show that when these sources are included in the inventory estimate for ethylbenzene emissions using appropriate scaling factors from previous Australian studies, then the emissions estimate for ethylbenzene is increased by approximately a factor of ten, and the ratios of this revised emissions estimate to those of the other BTEX gases are more consistent with atmospheric observations.