Doctors and public health experts agree that inhaling fine particulate matter (PM2.5) can be harmful to human health. Airborne particles – thirty times smaller than the width of a human hair – can easily pass into the lungs and bloodstream, where they can increase a person’s risk of death from heart disease, stroke, lung cancer, chronic obstructive pulmonary disease disease and infections of the lower respiratory tract.
However, current estimates of the total number of premature deaths associated with PM2.5 vary widely, from 3 to 9 million people each year. And there has long been uncertainty about the proportion of these deaths that are due to naturally occurring windblown dust versus human-caused (or anthropogenic) pollution that comes from factories, transportation, power plants, cooking stoves, crop fires, and other sources.
Research led by a team of atmospheric scientists based at NASA’s Goddard Space Flight Center shows that the health burden associated with PM2.5 is slightly lower than previous estimates have suggested—and sheds light on the role of dust. The researchers—including Hongbin Yu and Alexander Yang—calculated the global health effects of PM2.5 by analyzing exposure over an extended period of time using a NASA atmospheric modeling system integrated with medical data from the University of Washington’s Global Burden of Disease Study.
The NASA team’s conclusion: PM exposure2.5 likely contributed to 2.89 million premature deaths in 2019 – 1.19 million from heart disease, 1.01 million from stroke, 287,000 from COPD, 230,000 from lower respiratory tract infections and 166,000 from lung cancer lung. According to their estimates, approximately 43 percent of these deaths occurred in China and 23 percent in India, two of the world’s most populous and polluted countries. Other countries with significant exposure to HRV2.5 and high numbers of premature deaths include Pakistan, Bangladesh and Nigeria – although none of these countries account for more than three percent of total PM-related deaths2.5.
The analysis linked 22 percent of premature deaths to PM2.5 of dust – much of it in a “dust belt” that stretches from West Africa to East Asia. “Both in northern China and northern India, you have huge urban populations living downwind of the main dust sources,” explained Yu. “You also have this in West Africa and the Middle East to some extent, particularly in Nigeria and Egypt .”
The satellite image above shows a wall of dust from the Gobi desert approaching northeast China and the Beijing metropolitan area on March 10, 2023. The image below shows dust from the Thar desert blowing east over the densely populated Indo-Gangetic plain and mixed with smoke and haze from crop fires and urban pollution on April 7, 2021. Both images were obtained by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite.
“This study is a reminder that dust—something that is largely natural and something we cannot easily control with policy—can have an important impact,” said Yu. “In some countries in the dust belt, dust itself it can push the population’s PM2.5 exposure well above World Health Organization guidelines.”
The team reached their conclusions by first calculating how much background exposure people in different parts of the world would need to have to PM2.5 in 2019 using a meteorological and atmospheric reanalysis system called Modern Era Retrospective Analysis for Research and Applications Version 2 (MERRA-2). MERRA-2 is a model that uses real-world observations to simulate how dust and other key aerosol particles move and change in the atmosphere over time. The researchers checked the accuracy of the MERRA-2 results by comparing them to air quality measurements collected from the surface at US embassies and consulates around the world. They analyzed PM2.5 exposure in 2019 to ensure that changes in mortality related to the COVID-19 pandemic did not affect the results.
There are multiple ways researchers can represent the size and shape of dust particles in MERRA-2 and other atmospheric models, and the research team found that estimates of PM2.5 deaths are more accurate if calculations are based on aerodynamic particle size rather than geometric size.
“Aerodynamic size includes important information about the shape and density of dust particles, which is relevant to how easily the particles fall out of the atmosphere and move into the respiratory system,” explained Yu. Although the geometric size of dust, which is larger than aerodynamic size commonly used by atmospheric scientists, doing so in this type of health outcomes study would overestimate the number of deaths attributable to dust by about 1 million people, according to Yu.
Key sources of satellite data used to constrain MERRA-2 include the MODIS and Multi-angle Imaging SpectroRadiometer (MISR) sensors on NASA’s Terra and Aqua satellites. MERRA-2 covers the modern satellite era (1979 to present) and operates using the Goddard Earth Observing System (GEOS) model. At GEOS, airborne particles are simulated using the Goddard Chemistry Aerosol Radiation and Transport (GOCART) model.
NASA Earth Observatory images by Lauren Dauphin using MODIS data from NASA EOSDIS LANCE and GIBS/Worldview. Narrated by Adam Voyland.