In this study of homes of African American pre-school inner-city children, we found that indoor PM concentrations in the children’s bedrooms were twice as high as outdoor concentrations and in many cases, exceeded the EPA outdoor annual limit. Indoor activities, such as smoking and sweeping, were substantial contributors to indoor PM. It is notable for the goal of reducing indoor PM that these activities are modifiable. As expected, ambient PM concentrations were also positively associated with indoor concentrations. Consistent with our finding that the indoor PM concentrations were higher than simultaneously measured ambient levels, keeping windows open appeared to lower the PM concentration in home indoor air. Given that the in-home PM concentrations were elevated and that higher indoor PM concentrations have been linked to symptoms and lower lung function in children with asthma (Koenig et al., 2005
), these results can point to feasible PM reduction strategies to improve home indoor air quality in susceptible young children, including those with asthma.
Findings from the present study are consistent with certain findings reported previously by other investigators (Wallace, 1996
; Wallace et al., 2003
). Our study extends previous findings by focusing on an especially susceptible population, African-American pre-school children with asthma living in an inner-city environment. Smoking has been described as a major source of indoor particulate over the last several decades and our results suggest that smoking continues to be a significant contributor to PM exposure. The difference in PM2.5
of 26 μg/m3
is similar to the range of 25 to 45 μg/m3
that has been previously reported (Breysse et al., 2005
; Wallace, 1996
; Wallace et al., 2003
). It is disappointing that smoking has the same impact on indoor PM as it did in studies from several years ago, which demonstrates that in-home smokers are not taking effective precautions to limit the impact of smoking on the home environment. This observation implies that despite the known health risks of second hand smoke to very young children in the home (Cook et al., 1998
; Cook et al., 1999
; Corbo et al., 1996
; Mannino et al., 2001
; Moshammer et al., 2006
), parents are not taking precautions to protect their children and that public health messages have not effectively led to changes in smoking behaviors in the home.
Cooking activities have also been previously reported as a source of indoor PM (Ozkaynak et al., 1996
; Wallace et al., 2003
). However, we were not able to confirm such an effect in our study population by looking at stove use, oven use and reports of burned food. While we found a dose-response relationship between stove use and indoor PM levels, this was no longer significant after adjusting for other household activities in the multivariate model. The difference between the findings of our study and those of previous studies may be due, in part, to the method of environmental assessment. While previous studies have typically monitored a common living space, our study differs in that environmental monitoring was conducted in the children’s bedrooms which may have been farther away from the cooking area. Different methods of ascertaining household activities could also have contributed to the differences with respect to cooking activities. For example, in Wallace’s study, respondents were asked at the end of 2 weeks to report events that had occurred during monitoring, while we asked respondents to record events in a daily diary. It is possible that events recalled weeks after they occurred (e.g., an occasion of burned food) would be more intense, which could be more strongly tied to PM concentrations. Finally, regional or cultural differences in cooking methods could account for some of the differences between study results. As our study suggests that cooking activities are not predictive of elevated PM levels in the bedroom and previous findings suggest that indoor PM levels in common household areas are elevated in association with cooking, consideration should be given to moving children to more distant areas of the home during times that cooking occurs to avoid PM exposure.
A finding unique to our study, was the strong, independent effect that sweeping had on elevation of PM. Each sweeping event that was reported during the 3-day monitoring was associated with an increase in PM10 of 3-4 μg/m3. While household cleaning is necessary, our study suggests that the method of cleaning may be predictive of PM concentrations. Sweeping showed a significantly positive relationship with indoor PM concentrations while vacuuming did not. This distinction has not been previously reported to our knowledge and may have implications for future recommendations about strategies to limit PM concentrations. While use of vacuum cleaners, including those with HEPA filters, have not been shown to improve children’s asthma (Costovic and Wijk, 2005), our study findings would suggest that in the interest of keeping airborne PM concentrations lower, vacuum cleaners may be preferred to sweeping. Indeed, parents of children with asthma should be reminded that cleaning activities should ideally be performed when the child is out of the home.
Certain household conditions, including open windows, were associated with lower indoor PM concentrations. While a previous study reported that open windows reduced indoor PM in homes with smokers (Wallace et al., 2003
), we have extended this finding by showing this effect regardless of smoking status. It is notable that this finding applied to the exclusively urban community that comprised the study population, an environment where this finding might not be expected. While the use of air cleaners was rare in our study, they appeared to have a marked negative effect on indoor PM concentrations.
Our study has several strengths and weaknesses. Our study was designed to minimize recall bias by asking caregivers to complete an intensive survey (survey completed at least 3 times daily) about household activities over a relatively short duration of time (3-day monitoring period). Even this method can be affected by recall and by issues such as underreporting based on social desirability (e.g., may not want to reveal how much smoking actually occurs) which may have limited our ability to demonstrate certain associations. We recorded PM concentrations in the child’s bedroom, as this location was expected to represent the majority of time of in-home exposure. However, certain activities that generated PM occurred in other locations in the home so we may have underestimated the effect of certain sources of PM on other living areas (e.g., cooking activity and kitchen PM). Since our study was conducted entirely in an urban setting, mostly in row homes, we cannot be sure if similar associations would be found in other residential settings. Nonetheless, our findings are highly relevant to young, urban dwelling children, who are markedly affected by asthma in United States (American Lung Association. Lung Disease Data in Culturally Diverse Communities, 2005
The findings from the present study highlight that environmental recommendations given to those with respiratory disease should be quite specific. For example, current international guidelines recommend staying indoors as a means to avoid unfavorable outdoor environmental conditions (Global Strategy for Asthma Management and Prevention, 2006
). This advice is warranted as staying indoors on high ozone days will effectively limit ozone exposure (Gold DR et al., 996; Lee K et al., 2004
). However, the results of our study suggest that retreating indoors may not be an effective means of avoiding high PM exposure, even in homes without smokers. Thus, the recommendation should be carefully crafted to specify the characteristics of a favorable indoor environment.
In conclusion, our study demonstrated that in a population of inner-city, predominantly lower income, African-American pre-school children, common household activities and ambient PM both contribute to indoor PM concentrations. The children in our study spent a remarkable proportion of their time in their own homes, where they were exposed to PM concentrations that were markedly higher than those found outdoors. For children who are vulnerable to the effects of airborne PM, strategies to reduce PM exposure should include keeping the child away from the home when sweeping occurs, improved ventilation of the house including the use of open windows, and especially avoidance of indoor tobacco smoke. While it is clearly difficult for some families to implement complex or expensive modifications, this study points to a few simple, targeted changes that could have substantial impact on indoor air quality. Further studies are still needed to determine the most efficacious, feasible and affordable methods for improving indoor air quality for the sake of the respiratory health of young children.