Characterization Of Personal Exposure To Black Carbon In Urban Settings And Airway Response In Children

Black carbon (BC), which mainly results from incomplete combustion of biomass and fossil fuels, is responsible for significant climate, environmental and health effects in the atmosphere. BC with particle size ranging from0.1to1μm, can enter the respiratory system, possibly penetrating deep into the lungs; this might trigger asthma attacks or other diseases by causing airway inflammation. In recent years, scientific attention has shifted to the role of BC as a risk factor of human health.A mountain of epidemiological and toxicological studies implicate that exposure to BC is associated significantly with respiratory and cardiovascular diseases. In those studies, the assessment of exposure to air pollutants has been primarily based on ambient measurements. However, stationary data may not properly reflect personal exposure due to the differences in personal activities among different subjects and the spatial heterogeneity of the air pollutants measured (e.g. BC). Interpretation of findings from epidemiologic and toxicological studies has been hampered by uncertainties in exposures. Accordingly, much attention has been directed toward the need for more appropriate exposure assessment methodology. A detailed study on the characteristics of temporal and spatial distribution of BC in urban settings and the contribution of outdoor/indoor BC levels to personal BC exposure will help in gaining a better understanding of the extent to which fixed-site BC measurements are representative of personal exposure, which is essential to the validation of epidemiological studies that are based on stationary measurements as well as to the determining of the true association between BC exposure and human health.This study focuses on the characteristics of personal exposure to BC in urban settings. It validated a newly developed BC monitor-MicroAeth for personal BC exposure measurements and investigated for its application in personal exposure study. MicroAeth was used as a personal BC sampler in the study on relationship of personal BC exposure and airway response in Children in New York City (NYC) and in the study on characteristics of personal exposure to BC in a Shanghai (SH) subway station. Based on the outdoor/indoor BC monitoring and personal BC sampling in both NYC and SH, this study preliminarily compared characteristics of ambient BC distributions and personal BC exposures among two cities. Home indoor BC,6repetitions of personal BC measurements as well as lung function and exhaled NO data were collected from9-10years old children in NYC:multivariable linear regression was conducted to model the relationship between ambient, home indoor and personal BC; linear mixed effected models were conducted to estimate the relationship between personal BC exposure and airway acute response in9-10years old children in NYC. A preliminary comparison of outdoor/indoor BC and personal BC was conducted in the SH study. And it characterized the personal exposure to air pollutants in an enclosed space and assessed the long-term and short-term risks of BC exposure in different environments via conducting personal sampling on staff from a subway station in SH.The main results from this study are described below:(1) It is very apparent from central site BC and home indoor BC measurements that BC is temporally and spatially heterogeneous in NYC. Strong seasonal (higher BC levels in winter and summer than ones in spring and autumn) and weekly patterns (higher BC in weekdays than one in weekend) suggest that BC distribution in NYC is mainly affected by meteorological conditions and local sources; in contrast with BC distribution characteristics in NYC, the SH area seems to be significantly affected by contributions from regional and long distance transportation in addition to local BC sources(2) Comparison among ambient, home indoor and personal measurements show that ambient BC at central site can explain37%of variability of personal BC; while home indoor BC in non-heating season and heating season can explain59%and45%of variability of personal BC, respectively, suggesting that ambient BC and home indoor BC do not adequately reflect personal BC exposure of a cohort of NYC children; while home indoor BC performs better than ambient BC due to the fact that most of the subjects’ time is spent at home and BC concentrations are heterogeneously distributed in NYC. Hence, to accurately capture BC exposures of a cohort of NYC children, personal monitoring is essential.(3) Linear mixed effect model analysis shows that the lung function of FEVi/FVC and FEF2575/FVC will decrease0.8%and0.03with1μg/m3of personal BC increases among non asthmatic children, suggesting exposure to BC may have adverse effects on lung development in children without asthma; however, similar results were not observed in children with asthma. The levels of inflammation biomarkers were significantly associated with home indoor NO, but not with personal BC, suggesting that more attention needs to be paid on indoor air quality.(4) Similarly, it was concluded that outdoor/indoor BC do not adequately reflect personal BC exposure based on the comparison of stationary measurements and personal sampling conducted by staff working in a subway station in Shanghai. It suggested that the strength of exposure risk to BC in the Shanghai area varies greatly among different environments. Although BC levels in the dispatcher’s office in a subway station were relatively lower than in non-office environments, the exposure dose of personal BC was higher in the office probably due to the fact that subjects spent approximately72%of their workday in the office environment. Therefore, it indicated that the office should be considered as the priority environment for professional exposure risk study, while the non-office environment should be considered as the priority one for the study of public exposure risk.Overall, the following points stand out in this study:(1) As far as we are aware, the usage of the microAeth as a personal BC real-time monitor has not been validated in peer-reviewed literature. This study presented on the detailed analysis of the performance of the microAeth as a personal sampler under varying conditions of humidity and vibration. A post hoc procedure was developed to identify causes of and to remediate problematic BC readings for personal data quality assurance and control.(2) The repeated personal BC, lung function and inflammation biomarkers measurements obtained for each subject enables the use of the linear mixed effect model with random intercepts for random effect adjustment to investigate the relationship between BC exposure and airway response with much less uncertainty.(3) As far as we aware, a study on characteristics of personal exposure to BC in Shanghai subway stations has not been published in the scientific literature. This study characterized personal BC exposure in professional environments, i.e. a subway station, and assessed long-term and short-term exposure risks in different subway micro-environments by comparing personal BC levels and BC concentrations in an enclosed space. Furthermore, it provides information for the investigation of both professional and public exposure risk and provides a scientific basis for enacting measures for air pollution control.(4) This study stands out in its establishment of a complete exposure characterization, including ambient, indoor and personal measurements and provides a better understanding of proper BC exposure assessment.