Health Risk Of PM_2.5 Exposure In Urban Micro-Environments

Traditional epidemiologic cohort studies have confirmed that long term PM2.5 exposure is negatively associated with human health. Using ambient PM2.5 concentration as substitute of real exposure load may bring bias to the actual exposure-response relations and therefore the accuracy of health risk assessment, which ignores both the spatial disparities of PM2.5 concentration and duration of stay in various urban micro-environments. This study gathered information of residence, work/study and time-activity patterns through one-year field questionnaire survey to calculate time-weighted PM2.5 exposure of 14 kinds of micro-environments and achieve more scientific and thorough health risk assessment of fine particulate exposure. Besides, satellite-retrieved PM2.5 ground level data and Integrated Exposure Response (IER) model were applied to calculate attributed deaths of 4 health endpoints for the year 2000 and 2010. Main conclusions are as follow:i. Both PM2.5 concentration and its attributed deaths increased significantly in the past decade. Anthropogenic sources contributed over 90% of the death toll for both years. All-composition PM2.5 concentration rose from 49.49 μg/m3 in 2000 to 69.97μg/m3 in 2010 while the total attributed deaths rose from 2718 to 8757. According to the sensitivity analysis, population factor had greater influence on the attributed deaths comparing to concentration factor.ii. Among the six districts of Suzhou city, Wujiang (WJ) district had the most attributed deaths from 774 in 2000 to 2222 in 2010, whose proportion to the district population (representing attributed death risk) was 0.143% for the year 2000 and 0.295% for the year 2010 (other districts Yuanqu 0.149% and 0.294%, Gusu 0.114% and 0.294%, Gaoxin 0.121% and 0.292%, Wujiang 0.143% and 0.295%, Wuzhong 0.144% and 0.286%, Xiangcheng 0.136% and 0.290%), indicating positive relation with local population. Moreover, socioeconomic factors are also important considering the district with least attributed deaths converting from Yuanqu (YQ) district in 2000 to Gaoxin (GX) district in 2010. From the perspective of grid distribution, the attributed deaths clustered most in the densely-populated urban center in Gusu (GS) and YQ district and gradually decreased in the surrounding area, as well as more in the eastern than in the western region.iii. The time-activity patterns (TAPs) of Suzhou urban residents revealed obvious disparities affected by demographic (e.g., age and gender) and time (e.g., vacation, season and day of the week) attributes. Overall, people tent to spend more time indoors in winter and summer while less time indoors on weekends; male at all age periods spent more time outdoors than female; the elderly (>64 years old) spent more time outdoors than younger groups for all seasons. The average time spent indoors surpassed 80% for all groups of people with over 60% in the residence. Seasonal TAPs differ most for juveniles (<18 years old) due to vacation and profession factors; the elderly group spent more time outdoors in winter while less in summer unexpectedly. Besides, the communication media choice varied among different age and gender groups, indicating distinct life styles and exposure levels,iv. Based on the population distribution and TAPs of various demographic groups, micro-environment exposure load was calculated, which only accounted for 75%-80% of the ambient exposure, declaring that each kind of micro environment is of great significance, especially for residence and other indoor places (excluding office and classroom), contributing over 60% for all seasons and over 10%, respectively. This study has reflected the quantitative bias in the traditional epidemiologic researches. Future work should attach more importance to the impact of indoor/outdoor relationship of fine particles, indoor pollution sources and human activities as well.