Citation:

Astitha, M., H. Luo, C. Hogrefe, R. Mathur, AND S. Rao. Estimating the confidence bounds for projected ozone design values under different emissions control options. Meteorology & Climate - Modeling for Air Quality Conference, Sacramento, California, September 13 - 15, 2017.

Impact/Purpose:

The National Exposure Research Laboratory (NERL) Computational Exposure Division (CED) develops and evaluates data, decision-support tools, and models to be applied to media-specific or receptor-specific problem areas. CED uses modeling-based approaches to characterize exposures, evaluate fate and transport, and support environmental diagnostics/forensics with input from multiple data sources. It also develops media- and receptor-specific models, process models, and decision support tools for use both within and outside of EPA.

Description:

In current regulatory applications, regional air quality model is applied for a base year and a future year with reduced emissions using the same meteorological conditions. The base year design value is multiplied by the ratio of the average of the top 10 ozone concentrations for the base and future years (i.e., upper tail projection methodology) to assess whether the estimated future year design value meets the ozone standard. The SIP process requires that the adopted emissions control strategy would help meet and maintain the ozone standard no matter what meteorological conditions prevail in the future year. Because the same meteorological conditions would never prevail in future years and observations for the future year are not available, the current attainment demonstration methodology can never be evaluated in the real world. Here, we apply the CMAQ model to assess the reduction in the long-term forcing (i.e., ozone baseline concentration) stemming from reduced emissions and then superimpose the short-term forcing (i.e., synoptic-scale weather fluctuations) embedded in the historical ozone observations on that reduced baseline to reconstruct the ozone time series expected for the future year. For each emissions reduction case, we determine the reduction in the ozone baseline and possible design values for varying synoptic-scale weather forcings (i.e., baseline projection methodology), and examine the probability of achieving compliance with the ozone standard in the future year. We also evaluate the abilities of upper tail and baseline projection methodologies in capturing the observed design values at all monitoring sites in the future year.

Record Details: