Twin Cities Metropolitan Air Quality - Percent of National Standard Nature Uncategorized Chart of the Day – Air Quality David Levinson • April 14, 2014 Today’s Charts of the Day concern air quality. Twin Cities Metropolitan Air Quality – Percent of National Standard Comparison of growth areas and emissions in Minnesota – percent change since 1990. Source: MnDOT Annual Transportation Performance Report 2012 Share this:EmailFacebookTwitterRedditLinkedInMastodon Related