Implications of daily mobility around residence for air pollution assessment in peri-urban South India

Abstract

Individual time-activity is a crucial determinant of exposure to air pollutants. Most knowledge about mobility in relation to exposure misclassification is from high-income countries. Our aim was to analyse daily mobility of adults in a peri-urban area near Hyderabad, India, using continuous Global Positioning System (GPS) data to understand the implications of mobility on air pollution exposure assessment. As part of the CHAI project (Cardiovascular Health effect of Air pollution in India), 61 volunteers were invited to wear a GPS receiver during 6 sessions of 24 hours, from June 2015 to January 2016, recording position every 30s. Distance of each point from home and activity space features (standard deviational ellipse) were derived. Fifty six participants (92% participation, 50% women) completed at least 1 session, and were followed for 3.7 days on average. Daily activity space area showed high variability ranging from 31m2 to 108km2. Most points (82%) occurred within 100m of the home, with contrasts by sex (mean (±sd): 86% (±24) and 76% (±19) for women and men respectively; p<0.01), age (76% (±21), 79% (±22), 84% (±25) and 86% (±20) for age ≤24, 25-42, 42-51 and ≥52 years respectively; p=0.08) and occupation (90% (±24), 84% (±20) and 71% (±24) for unemployment, semiskilled manual and skilled manual/professional respectively; p<0.01). Women's mobility patterns were significantly more home-centred than men's (mean (±sd) distance from home to activity space centroid: 228m (±107) and 616m (±109) respectively; p<0.01 after adjustment for age and occupation). Overall, one third of total variation (intra class correlations) in travelled distance from home was explained within subject over time. Time-activity patterns were found to be more home-centred for this population than for typical populations in high-income countries. This result supports the relevance of home-based estimates of air pollutant exposure, particularly for women and older age groups.