Why is Ozone Low in Baltimore City?

1. Why is Ozone Low in Baltimore City? • In most cities, ozone is lower in city centers than it is downwind of the cities • Well established in the scientific literature • Chemistry and ground level winds from the southwest are both involved • Harford County records highest levels in Baltimore area • Anne Arundel County for Washington D.C. • Same pattern for every East Coast City

2. What do Scientists Say? • On low levels in cities “… in many instances there are low VOC/NOx ratios that lead to depressed ozone concentrations within the central core.” • Rethinking the Ozone Problem in Urban and Regional Air Pollution, National Research Council, 1991 • “Ozone tends to reach higher concentrations downwind of major pollutant emitters, that is, concentrations in suburban or rural areas near cities are often higher than in downtown areas.” • Dr. Russell R. Dickerson, Ph.D., Professor and Chairman, Department of Atmospheric and Oceanic Science, The University of Maryland, 2006 • “The highest ozone concentration in Washington DC, Baltimore and Philadelphia metropolitan areas are not in the urban centers, but are downwind of the cities and their suburbs.” • A Guide to Mid-Atlantic Regional Air Quality, MARAMA 2005

3. More Data • On “Bad Air” (exceedance) days – on average: • Peak 1-hour concentrations in Baltimore City are about 37 parts per billion (ppb) lower than other monitors • 25.6 ppb lower for 8-hour • On all summer days: • Peak 1-hour ozone concentrations in Baltimore City are about 19 ppb lower than other monitors • 17 ppb lower for 8-hour • Is this always true? • There was one day (in 1995) when a city monitor violated the 1-hour standard and all the other surrounding county monitors recorded levels below the standard • Never seen this with 8-hour ozone