Hybrid Plume/Grid PM_(2.5) Attainment Demonstration Modeling for the Allegheny County, PA PM_(2.5) SIP

摘要

The Liberty-Clairton Nonattainment Area (NAA) lies in Allegheny County, Pennsylvania approximately 10 miles southeast of Pittsburgh. The Liberty-Clairton NAA violates the 24-hour 35 μg/m~3 PM_(2.5) National Ambient Air Quality Standard (NAAQS) based on 2009-2011 observations. The Allegheny County Health Department (ACHD) is preparing a PM_(2.5) State Implementation Plan (SIP) that demonstrates the Liberty-Clairton NAA will attain the 24-hour PM_(2.5) NAAQS by 2014. Both regional as well as local sources contribute to PM_(2.5) exceedances at the Liberty monitoring site. The Comprehensive Air-quality Model with extensions (CAMx) is a one-atmosphere multi-scale photochemical grid model that includes a subgrid-scale Plume-in-Grid (PiG) chemically reactive Gaussian puff model to treat the near source plume dynamics and chemistry within point source plumes. CAMx was applied for 36 km Continental U.S., 12 km Eastern U.S., 4 km Southwest Pennsylvania and 800 m Liberty-Clairton region domains and the 2007 annual period to address attainment of the PM_(2.5) NAAQS. Local sources were treated using the Plume-in-Grid (PiG) subgrid-scale puff module with the PiG puffs sampled using a 100 m receptor array located around the Liberty monitoring site. The Particulate Source Apportionment Technology (PSAT) was used to track the local source contributions to PM concentrations after the emissions were released from the PiG module to the grid model. The CAMx 2007 base case simulation was subjected to a model performance evaluation that revealed good model performance for PM_(2.5), sulfate and ammonium. Several procedures were used to project the observed 2005-2009 24-hour PM_(2.5) Design Values to 2014. 2014 PM_(2.5) projections were made using both the hybrid CAMx plume/grid modeling system as well as separately projection the local and regional components of the PM_(2.5) using the, respectively, PiG reactive plume and CAMx grid models, where the local source contribution was removed from the CAMx results using the PSAT PM source apportionment results.