Long-Term Aerosol Trends in the Continental United States
Aerosols from U.S. industrial sources have decreased in recent decades. However, changes in emissions in other regions of the world also influence U.S. aerosol trends through long-range transport. A study led by scientists at the U.S. Department of Energy’s Pacific Northwest National Laboratory revealed the influence of domestic and foreign emissions on trends of aerosols and their effect on energy balance in the United States from 1980–2014. Researchers found that, in the western United States, increases in aerosols from East Asia decreased the radiative warming effect induced by reductions in U.S. emissions by 25 percent.
Because they can either absorb or reflect energy, aerosols are important components influencing air quality and atmospheric changes. Quantifying the source of aerosols and their influence on energy balance is necessary for predicting future air quality and Earth system changes. As industrial aerosols decrease in the United States, foreign emissions become increasingly influential on the energy balance over the country.
As a result of air quality regulations, aerosol emissions from North American and European countries have decreased during recent decades. In the meantime, emissions in developing countries (e.g., in East Asia and South Asia) have significantly increased because of rapid industrial and population growth. The relative roles of domestic and foreign sources in changing aerosol concentrations and energy balance over the United States in recent decades are still not clear.
Researchers quantified the relative roles of multi-decadal U.S. pollution control programs and changes in emissions in other regions of the world on aerosol concentrations and energy balance over the continental United States for the time period of 1980−2014. To do this, they used an aerosol source tagging capability in the Community Atmosphere Model (version 5), a global aerosol-climate model. Researchers found that increases in emissions from East Asia decreased the warming effect (e.g., radiative forcing) induced by reductions in U.S. aerosol emissions by 25 percent in the western United States, but had a more modest impact on U.S. air quality through changes in surface concentrations.