Aspects of ozone transport, mixing, and chemistry in the greater Maryland area

Abstract

This study examined the role of ozone transported and the subsequent mixing of the transported ozone on the ozone concentration and chemistry in the surface layer at locations in central Maryland. Surface data from the United States Environmental Protection Agency's (EPA) Aerometric Information Retrieval System (AIRS) database, ozone profile data from the University of Maryland's aircraft measurements, trajectory analyses using the HYSPLIT model, and predictions using the Semi-Empirical Integrated Pollution Model (SIPM) for the periods 11–15 July 1995 and 12–16 July 1997 were used to meet the objectives of this study. It was found that on the day before the air mass reached the receptor in Maryland, the air mass passed over regions where the diurnal maximum ozone concentration was sufficiently large and the mixing sufficiently deep, in most cases, to have been the primary source of the ozone that was found over central Maryland the next morning. Mixing took place between the air mass above the nocturnal inversion and the surface layer when the nocturnal inversion broke down sometime after sunrise, and the ozone in the surface layer increased by about 13 ppb, on average, as a result of the mixing. The results also showed that when certain conditions were met, the chemistry in the surface layer produced up to about three times more ozone when mixing of ozone into the surface layer took place and when a non-zero value for the diurnal minimum zone concentrations were used to initialize the chemistry. There were, however, a number of situations when mixing of ozone into the surface layer and when a non-zero value for the diurnal minimum ozone concentrations were used to initialize the chemistry, had little effect on the surface ozone layer. The conditions, under which both situations occurred, are discussed.