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<p><strong>Abstract.</strong> Observations at national parks and other remote sites show that average elemental carbon and fine particle mass concentrations in the United States both decreased by over 25 % between 1990 and 2004. Percentage decreases in elemental carbon were much larger in winter than in summer. These data suggest that emissions controls have been effective in reducing particulate concentrations not only in polluted areas but also across the United States. Despite the reductiondoi:10.5194/acp-11-4679-2011 fatcat:g45zxj7kzvh2jm7v5idysmp6xa