A new NASA study calculates that nearly 64 million tons of dust, pollution, and other tiny particles enter the atmosphere above North America from other continents each year, nearly as much as the 69 million tons of 
aerosols produced domestically through natural processes and human activities. The vast majority of the particles entering the atmosphere, scientists say, consist of natural dust and not pollutants. In a first-of-its-kind study, NASA researchers used satellite data and wind speed estimates to calculate that about 88 percent of the microscopic particles, or 56 million tons, consists of dust carried in wind currents, particularly during the spring when an increase in cyclones and mid-latitude westerlies propel powerful atmospheric currents across the Pacific Ocean. According to the study, published in the journal Nature, about 60 to 70 percent comes from Asia, and the remaining 30 to 40 percent comes from Africa and the Middle East. But only about 5 percent of the dust drops within the lowest 1.2 miles of the atmosphere, where it can be inhaled by humans. NASA scientists say the study provides critical insights into how aerosol particles across the planet affect air quality and the climate.
NASA