# **1.  Introduction**

Outdoor air pollution is a major source of health damage in developing countries. The World Health Organization (2016) attributes about 3.3 million annual premature deaths to outdoor air pollution in low- and middle-income countries: 72% from heart disease and strokes, 14% from chronic obstructive pulmonary disease, and 14% from lung cancer. The World Bank (2016) estimates welfare losses from ambient fine particulate and ozone pollution at 4.8% of GDP equivalent in East Asia, 3.5% in South Asia, 2.1% in the Middle East and North Africa, 1.6% in Latin America and 1.5% in Sub-Saharan Africa.

Pollution problems are essentially geographic, because their incidence and impacts depend on the spatial distributions of economic activities, topography, weather and households. Although researchers and policy makers are sensitive to this spatial component, incomplete information has hindered their attempts to identify and implement cost-effective strategies for pollution control. Local pollution is often poorly measured because monitoring systems are sparse, costly and difficult to maintain. Since this problem is pervasive in developing countries, rigorous empirical analyses of alternative strategies are rare. For decision making, policy makers need frequently updated information on the sources, dispersion and distributional implications of pollution.

In recent years, several new global information sources have offered a potential escape from this information trap. For example, high-resolution satellite imagery permits frequently-updated observations of polluting aerosols worldwide. Appropriately mobilized and interpreted, data from such sources could elevate the state of the art in pollution research, policy analysis and implementation. However, before these sources come into widespread use, empirical tests are needed to assess their operational utility, including accuracy testing against benchmarks provided by ground-based measurement.

This paper assesses the potential for low-cost augmentation of ground-based air quality monitoring in Dhaka, Bangladesh, with more comprehensive coverage from global information sources. We test the potential contributions of two satellite information platforms: Sentinel-5P, operated by the European Space Agency (ESA), and NASA’s MODIS. Our assessment includes four dimensions: (1) Goodness-of-fit to ground-monitoring data; (2) spatial resolution; (3) update frequency; and (4) cost. We also investigate the potential contribution of Google Traffic in a spatial panel estimation exercise that relates traffic congestion to outdoor air pollution in the Dhaka region.<sup>1</sup> The remainder of the paper is organized as follows. Section 2 introduces prior research on the health impacts of PM2.5 and NO2. In Section 3, we introduce the data sources for our analysis. Section 4 uses econometric modeling to test the relationships between locally-monitored air pollution and measures provided by Sentinel-5P, MODIS and Google Traffic. Section 5 assesses the predictive accuracy of the estimated models. Section 6 discusses the relative benefits and costs of the new data sources, while Section 7 summarizes and concludes the paper.

> 1 In a global study, Dora et al. (2011) find that urban road transport often accounts for more than 50% of dangerous outdoor air pollutants (e.g., fine particulates, nitrogen oxides, carbon monoxide, ozone, sulphur dioxide).

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