Separating personal exposure from indoor and outdoor sources in a large London cohort (a part of MELONS* project)

Abstract

BACKGROUND AND AIM: Traditional time-series studies use ambient measurements as a proxy for personal exposures. Yet this accounts for neither the different time activities of individuals nor the spatial heterogeneity of the pollutants. Hence it introduces exposure measurement error and produces bias in epidemiological studies. Instead, we propose the use of personal exposure to outdoor sources as a better proxy was proposed as it is not affected by indoor sources and is important for policy intervention. This study aims to separate personal exposure of outdoor sources from indoor sources in a large London cohort. METHODS: The London cohort was formed by four large field campaigns within London. It comprises over 200 million linked and validated 1-minute mean measurements of gaseous (NO, NO2, CO, O3) and particulate (BC, PM2.5, PM10) pollutants, from 130 Chronic Obstructive Pulmonary Disease (COPD) patients continuously measured for six months, 40 healthy adults continuously measured for seven days, 250 primary age children and 140 professional drivers continuously measured for four days. We integrated the pollutant database, clustered GPS measurements, performed location tagging on one-minute data, then calculated monthly home infiltration efficiency. Using this information, we estimated participants’ personal exposure from indoor and outdoor sources. RESULTS:These COPD patients spent the majority of their time at home (on average 92%). The daily mean (±SD) personal exposure from indoor sources and from outdoor sources for these COPD participants were 4.9 ± 3.7 and 8.1 ± 6.1 µg/m3. CONCLUSIONS:Personal exposures were separated into indoor and outdoor sources for COPD patients in London and will be extended to other subgroups. Personal exposure from outdoor sources, regardless of the time they actually spent outdoors, was the main source of pollution exposure for these COPD patients. Separating sources of personal exposure allows separate examinations on the associations of health effects and more targeted pollution control interventions. KEYWORDS: personal exposure, outdoor sources, indoor sources, measurement error