Air pollution associated respiratory mortality risk alleviated by residential greenness in the Chinese Elderly Health Service Cohort.

Background: Although residing in lower surrounding greenness and transient exposure to air pollution are independently associated with higher risk of adverse health outcomes, little is known about their interactions.

Objectives: We examine whether residential neighborhood greenness modifies the short-term association between air pollution and respiratory mortality among the participants of Chinese Elderly Health Service Cohort in Hong Kong.

Methods: We estimated residential surrounding greenness by measuring satellite-derived normalized difference vegetation index (NDVI) from Landsat within catchments of residential addresses of participants who died of respiratory diseases between 1998 and 2011. We first dichotomized NDVI into low and high greenness and used a time-stratified case-crossover approach to estimate the percent excess risk of respiratory mortality associated with fine particulate matter (PM), respirable particulate matter (PM), nitrogen dioxide (NO), and ozone (O). We further classified NDVI into greenness quartiles and introduced an interaction term between air pollution and the assigned median values of the NDVI quartiles into the models to assess the trend of greenness modification on the air pollution and respiratory mortality associations.

Results: Among 3159 respiratory deaths during the follow-up, 2058 were from pneumonia and 947 from chronic obstructive pulmonary disease. Elders living in the low greenness areas were associated with a higher risk of pneumonia mortality attributed to NO (p = 0.049) and O (p = 0.025). The mortality risk of pneumonia showed a decreasing trend for NO (p for trend = 0.041), O (p for trend = 0.006), and PM (p for trend = 0.034) with greenness quartiles increasing from Quartile 1 (lowest) to Quartile 4 (highest).

Conclusions: Our findings suggest that elders living in higher greenness areas are less susceptible to pneumonia mortality associated with air pollution, which provides evidence for optimizing allocation, siting, and quality of urban green space to minimize detrimental health effects of air pollution.