Effects of Heating Season on Residential Indoor and Outdoor Polycyclic Aromatic Hydrocarbons, Black Carbon, and Particulate Matter in an Urban Birth Cohort

Abstract

Exposure to air pollutants has been associated with adverse health effects. However, analyses of the effects of season and ambient parameters such as ozone have not been fully conducted. Residential indoor and outdoor air levels of polycyclic aromatic hydrocarbons (PAH), black carbon (measured as absorption coefficient [Abs]), and fine particulate matter <2.5 μm (PM)(2.5) were measured over two-weeks in a cohort of 5-6 year old children (n=334) living in New York City's Northern Manhattan and the Bronx between October 2005 and April 2010. The objectives were to: 1) characterize seasonal changes in indoor and outdoor levels and indoor/outdoor (I/O) ratios of PAH (gas + particulate phase; dichotomized into Σ(8)PAH(semivolatile) (MW 178-206), and Σ(8)PAH(nonvolatile) (MW 228-278)), Abs, and PM(2.5); and 2) assess the relationship between PAH and ozone. Results showed that heating compared to nonheating season was associated with greater Σ(8)PAH(nonvolatile) (p<0.001) and Abs (p<0.05), and lower levels of Σ(8)PAH(semivolatile) (p<0.001). In addition, the heating season was associated with lower I/O ratios of Σ(8)PAH(nonvolatile) and higher I/O ratios of Σ(8)PAH(semivolatile) (p<0.001) compared to the nonheating season. In outdoor air, Σ(8)PAH(nonvolatile) was correlated negatively with community-wide ozone concentration (p<0.001). Seasonal changes in emission sources, air exchanges, meteorological conditions and photochemical/chemical degradation reactions are discussed in relationship to the observed seasonal trends.

Fig. 1

Seasonal variations in (a) Σ₈PAH_nonvolatile and (b) Σ₈PAH_semivolatile concentrations. T-tests were performed to compare heating season and nonheating concentrations of log-transformed Σ₈PAH_nonvolatile and Σ₈PAH_semivolatile indoors and outdoors. The white and black lines show individual observations, while the white and black area show the distribution. The dotted line indicates the overall geometric mean and the thicker solid line shows the geometric mean concentration of indoors and outdoors for each season. **p<0.001, t test. Σ₈PAH_nonvolatile includes benzo(a)anthracene (BaA), chrysene/iso-chrysene (Chry), benzo(b)fluoranthrene (BbFA), benzo(k)fluoranthrene (BkFA), benzo(a)pyrene (BaP), indeno(c,d)pyrene (IP), dibenzo(a,h)anthracene(DahA), and benzo(ghi)perylene(BghiP). Σ₈PAH_semivolatile includes pyrene (Pye), phenanthrene (Phe), 1-methylphenanthrene (1Meph), 2-methylphenanthrene (2Meph), 3-methylphenanthrene (3Meph), 9-methylphenanthrene (9Meph), 1,7-dimethylphenanthrene (1,7DMeph), and 3,6-dimethylphenanthrene (3,6DMeph).

Fig. 2

Median indoor (I) to outdoor (O) ratio. Median values of I/O ratio for each individual PAH, Abs, and PM_2.5 presented separately by season. *p<0.05 and **p<0.001, Mann-Whitney test.

Fig. 3

Associations between ambient ozone and outdoor (a) S₈PAH_nonvolatile, and (b) S₈PAH_semivolatile. The average ambient ozone data over the corresponding two-week sampling period for each subject were used. The linear regression analysis was performed between ozone concentration and log-transformed outdoor S₈PAH_nonvolatile and S₈PAH_semivolatile concentration.