OTAG Air Quality Analysis Workgroup Volume I: EXECUTIVE SUMMARY Dave Guinnup and Bob Collom, Workgroup co-chair “Telling the ozone story with data”

Workgroup Objective The Workgroup is to provide assessments of air quality and meteorological data relevant to the mission of OTAG. OTAG mission: To understand the role of transported ozone and precursors in the current ozone nonattainment problem

Description of the Air Quality Analysis WG AQA WG members were affiliated with EPA, state agencies, industry (power,transportation), consultants, academia Members were analysts or research managers generally representing their organizations (??) Interaction occurred through meetings, conference calls (monthly), and Sharing of reports, data and comments was conducted through the AQA-WG interactive web site. (

Types of Analyses Spatial pattern percentile analyses Trajectory residence time analyses Spatial, temporal correlation analyses Statistical cluster analyses Model/data comparisons Tracer analyses Temporal pattern and trends analyses Meta analysis: analysis of analysis Results integration

Problem Statement Some nonattainment areas (e.g. NE corridor, Lake Michigan) experience considerable influx of ozone across their boundaries They cannot demonstrate nonattainment by local measures only Significant ozone reductions at their boundaries will also be necessary From the OTAG Background Document:

Exceedance Areas for 1hr-120 ppb and 8-hr-80 ppb Standards

Area source NOx emissions are highest near cities. Point sources dominate the center of OTAG

The corners of the OTAG domain are mostly at tropospheric background levels Average 1-hour daily maximum ozone concentration in the OTAG region. All four corners of the region have about ppb ozone concentration which corresponds to tropospheric background entering the region.

Generally increasing trend from west to east in the direction of the prevailing air transport West-east cross-section through Kansas-Ohio-Maryland. Note the accumulation of ozone from west to east.

Highest (90 %-ile) O 3 occurs near urban areas. Lowest (10 %) ozone is high in the central domain Spatial pattern of the 10th percentile of daily max. ozone. Elevated ozone concentrations are evident throughout the central OTAG region. Spatial pattern of the 90th percentile of daily max. ozone. Highest ozone occurs near metropolitan regions.

The largest ozone variability (90-10 %-ile difference) occurs near urban areas.

High O 3 (90%-ile) days are associated with stagnation in the S.E. and transport in the N.E. Transport wind vector during high ozone days occurs when the winds are slow and variable, except in the Northeast where they occur during westerly winds.

Low O 3 (10%-ile) days are associated with transport from outside into the OTAG domain. Transport wind vector during low ozone days indicate transport of clean air from outside the OTAG region.

OTAG-wide episodes tend to be associated with stagnation followed by transport.

Transport in the N.E. occurs in synoptic, channeled, and near surface flow regimes

AQ data analysis suggest days between emissions and removal and mile transport Regions of impact based on one and two day ozone lifetime.

Model-derived transport scales are miles. Is model underestimating ozone transport?

Ozone events last longer in the South (2-3 days) and shorter (1-2 days) in the North.

OTAG is a well defined control region. Low O 3 air comes from outside, high O 3 air from inside OTAG. Back trajectories for receptor sites for low ozone days point to outside the OTAG region as the source of low ozone. Back trajectories for receptor sites for high ozone days point to the central OTAG region as the source of high ozone.

Emission changes do change O 3 levels. 120 ppb exceedances are 3X higher on Fridays than Sundays Exceedances on Fridays.Exceedances on Sundays.

Long-term O 3 trends also show that many control efforts have reduced the ozone levels

Control of sources in central OTAG domain may provide downwind benefits in all directions.

Conclusions Transport is real, characterized by time and space scales as noted Spatially, transport from central portion of OTAG domain more closely associated with high ozone levels Model may understate transport impacts -- interpret results accordingly