Assessment of the Contribution of Stratospheric Ozone to Ground-Level Ozone Concentrations

摘要

This assessment is concerned with the possible contributions of ozone transported from the stratosphere through the troposphere down to ground level to the episodic and longer term ozone concentrations measured in urban and rural areas. The episodic impacts would be of concern with respect to the possible occasions when the primary National Ambient Air Quality Standard for ozone would be exceeded. The larger term average could also contribute to episodic concentration levels, but also are of possible importance in terms of adverse effects on crop yields or forest growth. It is concluded that direct stratospheric ozone intrusions which can result in ozone concentrations exceeding 120 ppbv appear to be extremely infrequent. Stratospheric ozone can contribute to longer term average background ozone concentrations at ground levels locations. It is estimated based on 7 sup Be to O3 and 90 sup Sr to O3 ratios available that during the summer months 15 ppbv or less of the ozone measured may originate in the stratosphere. In early spring stratospheric ozone is likely to make a larger contribution relative to other sources. Ozone produced in the troposplume by photochemical reactions involving anthropogenic precursors can contribute during the summer a substantial part of the ozone down to ground level locations.