Global Distribution of Column Satellite Aerosol Optical Depth to Surface PM2.5 Relationships

Sundar Christopher,Pawan Gupta

doi:10.3390/rs12121985

Abstract

Using a combined Terra and Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) mid-visible aerosol optical depth (AOD) product at 0.1 × 0.1-degree spatial resolution and collocated surface PM2.5 (particulate matter with aerodynamic diameter smaller than 2.5 μm) monitors, we provide a global five-year (2015–2019) assessment of the spatial and seasonal AOD–PM2.5 relationships of slope, intercepts, and correlation coefficients. Only data from ground monitors accessible through an open air-quality portal that are available to the worldwide community for air quality research and decision making are used in this study. These statistics that are reported 1 × 1-degree resolution are important since satellite AOD is often used in conjunction with spatially limited surface PM2.5 monitors to estimate global distributions of surface particulate matter concentrations. Results indicate that more than 3000 ground monitors are now available for PM2.5 studies. While there is a large spread in correlation coefficients between AOD and PM2.5, globally, averaged over all seasons, the correlation coefficient is 0.55 with a unit AOD producing 54 μgm−3 of PM2.5 (Slope) with an intercept of 8 μgm−3. While the number of surface PM2.5 measurements has increased by a factor of 10 over the last decade, a concerted effort is still needed to continue to increase these monitors in areas that have no surface monitors, especially in large population centers that will further leverage the strengths of satellite data.

Highlights

Tropospheric aerosols are ubiquitous in the atmosphere
Even when no ground monitors are available, the satellite aerosol optical depth (AOD) coupled with appropriate meteorology (Equation (1)) can provide the best estimate of surface PM2.5
In 2003, Wang and Christopher reported that Moderate Resolution Imaging Spectroradiometer (MODIS) satellite data and products have a high potential for estimating surface PM2.5 concentrations

Summary

Introduction

Tropospheric aerosols are ubiquitous in the atmosphere. With particle diameters ranging from nanometers to several hundred micrometers, and with varying lifetimes, these aerosols have major impacts on climate [1], air quality [2], ecosystems [3], and health [4]. Satellite imagery over the last few decades have provided spectacular views of dust storms, biomass burning smoke, volcanic ash, and pollution aerosols near and far downwind of source regions. Particulate matter with aerodynamic diameters (The aerodynamic diameter of a particle is that of a sphere with density of 1 g per cm which settles in air at the same velocity of the particle under consideration.) less than 2.5 μm (i.e., PM2.5) is the sixth-highest risk factor for premature deaths and is one of the most pressing environmental issues facing human health [5]. Research over the last decade continues to show the important links between increased PM2.5 and mortality rates, and exposure to PM is one of the important environmental factors for the global burden of disease [7,8]

Objectives

Methods

Results

Conclusion