A case study of ozone production in a rural area of central ontario

Abstract

An O 3 episode observed at Dorset, a rural site in central Ontario, during a stagnant high pressure period of the intensive Eulerian Model Evaluation Field Study (EMEFS), in the summer of 1988, is simulated using a photochemical box model with a two-layer treatment. In the model analysis, natural hydrocarbon chemistry is simulated based on an isoprene-only scenario. Sensitivity tests indicate that local isoprene emissions are an important contributor to local O 3 production, relative to anthropogenic hydrocarbons (AHCs), during the event. The model calculated isoprene contribution to the local O 3 production, defined as the ratio of the O 3 amount formed in the absence of AHCs to that in the presence of AHCs, is characterized by a strong NO x dependence. A minimum value (∼50%) of the contribution was found at a NO x level of ∼ 6 ppbv for the representative hydrocarbon composition during the episode. At this NO x level, O 3 production was strongly influenced by the presence of AHCs. At significantly higher or lower NO x levels, isoprene is more important than AHCs in the local O 3 production.