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.

Air pollution (comprising household [HAP] and ambient air pollution [AAP]) is a major cause of premature death globally. In China and other low- and middle-income countries (LMICs), HAP has decreased gradually, but AAP has increased significantly from rapid industrialisation and urbanisation. Existing estimates of air pollution on health risk in LMICs have been extrapolated from studies in Western populations where the source and patterns of exposures differ substantially. Reliable of health effects of air population should include changing exposure patterns (from HAP to AAP) and time delay from exposure to disease onset, which will be best addressed by large prospective cohorts with detailed lifestyle (e.g. smoking), high quality air pollution data and linkage to disease outcomes. Our long-term plan is to apply cutting-edge approaches to enhance exposure data already collected in 0.5M China Kadoorie Biobank (CKB) adults to assess the health effects of air pollution across 10 diverse urban and rural areas in China.

We propose a 2 year collaborative feasibility study to evaluate enhancements in exposure assessment before scaling up across all of CKB. We will measure real-time ambient and household fine particulate (PM2.5) and carbon monoxide, using wearable and static devices, for 300 CKB participants from 3 (2 rural, 1 urban) regions, each for two 5-day periods at different times of the year. We will develop methods to assign individual ambient PM2.5 levels in 1 urban region (Suzhou) by linking geocodes of residential addresses to an exposure model constructed using national air monitoring and satellite remote sensing data. Such data will be related through individual-based time-series analyses to a range of disease outcomes to yield initial evidence about health risks of air pollution. Data collected and experience gained should provide the basis for a large-scale and long-term research programme into the hazards of air pollution in China and other LMICs.

This proposal builds upon a long-standing collaboration between Oxford University and China, contributing greatly towards Chinese research capacity building, helping to develop and enhance expertise in population health in China. This project will foster and strengthen exchanges between the two countries, involving international experts with a demonstrated commitment to sharing knowledge and skills. The collaboration will lead to important findings, with clinical and public health relevance, and future benefits to the health and well-being of the Chinese population (as well as of other populations).

Who will benefit from this research?

The key beneficiaries are:

- Public, with improved awareness of health consequences of air pollution, may lead to behavioural changes (e.g. cooking habits, improved ventilation, and use of clean fuel); and with improvements in environmental policy (see below), will experience reduced morbidity and mortality associated with house and ambient air pollution.

- Environmental policy makers, who can exploit reliable estimates of air pollution and risk of disease from CKB to guide national policy actions for reducing the disease burden from air pollution.

- Scientists, who will acquire new data to calibrate questionnaire data to proxy objective measures of air pollution, which can be used in other large epidemiological studies to provide reliable estimates of health associated with air pollution.

How will they benefit?

China's 2030 Sustainable Development Goals include reducing non-communicable disease mortality by a third, and monitoring the changes over time. However, there is major evidence gap regarding current and future air pollution associated disease burden. In recent years, various estimates have been reported about the number of deaths attributed to ambient air pollution (AAP) in China, which varied by 5-fold from <0.3 million to 1.5 million annually. For household air pollution (HAP), current estimates for China are mainly based on extrapolation of results from studies conducted in previous decades where patterns and magnitude of exposure differed substantially from those in recent decades or on extrapolations from studies conducted in Western populations.

Chinese policymakers in charge of environmental protection and health are aware of the evidence gap and the need to generate nationwide reliable estimates of exposures and health outcomes associated with the exposures. Our study has the unique potential to provide reliable long-term quantitative estimates of mortality and morbidity burdens associated with exposure to HAP and AAP in China. The information generated will help policymakers to assess the magnitude of problem and where to target their policy actions for reducing the disease burden more effectively. By demonstrating reliably the risks associated with exposure to HAP and AAP, it will encourage positive behavioural changes at the individual level to reduce exposure to HAP (e.g. cooking habits, improved ventilation and use of clean fuel).

The 2015 World Health Assembly called for further evidence with enhancement in collection and utilisation of air pollution exposure data (which are particularly lacking in low- and middle-income countries). By applying and developing various novel techniques and analytic methods for improved exposure assessment, our study will make a significant contribution to fulfil the goal. It will also contribute importantly to the research community by demonstrating the great added values and cost saving of incorporating individual air pollution exposure measures in the context of an existing large-scale prospective cohort study. It will also generate new and rich dataset to enable scientists from China and elsewhere to make novel discoveries, benefiting the human health globally.

Please refer to Pathway to Impact for more detailed on impact of our research on global communities including various Chinese stakeholders.