Assessing health risks associated with exposure to household and ambient air pollution in rural and urban China Air pollution is an important cause of ill-health worldwide. This is particularly the case in China and many other developing countries, in which outdoor air pollution is worsening due to increased traffic and industrial activities. Furthermore, many people still use solid fuels (e.g. wood, charcoal or coal) for cooking and heating in rural areas, generating harmful smoke and other toxic substances inside the home. Although we know that air pollution causes death and illness at the population level, the exact extent is not fully understood because accurate information is lacking. Reliable estimation of the disease risks arising from air pollution requires measurements of individual exposures to air pollution and their subsequent disease outcomes (i.e. onset of new diseases and death). We propose to address this knowledge gap using the China Kadoorie Biobank (CKB), a large study of 500,000 men and women recruited from 10 diverse urban and rural areas in China in 2004-08 with detailed tracking of disease outcomes as a resource to study the health effects of air pollution. This represents an efficient approach that avoids the need to generate a separate expensive study to conduct this work.   Use of CKB in this way requires improvements to existing air pollution data. As in many other large scale epidemiological studies, CKB did not directly measure actual air pollution levels individually, but relied on participants to report information on the type of fuel they use for cooking or heating and how often, or how close to a main road they live. Since individuals spend a varying amount of time in different locations doing various activities, this may be inaccurate measure of individual air pollution. The ideal would be to measure in real time the pollutant concentrations in the air breathed by each person individually. However, this will be impractical in a study of 0.5 million participants, so the challenge is to achieve estimates of exposure in a cost-effective manner. This proposal represents a pilot project to test and assess different methods of measuring individual exposure to household and ambient air pollution.  In this project we will ask 300 CKB participants from 2 rural and 1 urban regions to carry a small wearable monitor with them to record particle pollutant concentration for two 5 day periods in both warm and cool seasons of the year. In addition, we will ask them to note what activity (e.g. cooking, commuting) they are doing, the duration and the location, so that we can understand how much of their pollution exposure comes from indoor or outdoor environments. Because it could be difficult and expensive to ask each participant to wear a monitor, we will also test whether it is sufficient to estimate individual air pollution by using data from ground monitoring networks, supplemented by satellite remote sensing technology. Two of the many satellites orbiting Earth carry sensors that detect infrared light transmitted through the atmosphere, providing a measure of airborne particulate matter. Using information from satellites and ground monitors, we will create a more complete map of air pollution. We will test and optimise this new approach in Suzhou, an urban CKB site that already has good coverage of ground-based pollution monitoring data. Based on the residential addresses of study participants, we can use this air pollution map to estimate an individual's ambient exposure level. We will use this information to carry out an analysis to investigate the health effects of air pollution in Suzhou participants.   This proposal will provide important new understanding and experience needed to plan a larger project involving all 0.5 million participants in CKB. Ultimately we aim to collect reliable exposure and disease outcome data to accurately understand the impact of air pollution on health in China. The Global Challenges Research Fund (GCRF) supports cutting-edge research to address challenges faced by developing countries. The fund addresses the UN sustainable development goals. It aims to maximise the impact of research and innovation to improve lives and opportunity in the developing world.