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

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

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