Abstract

The Southern New Mexico Ozone Study (SNMOS) is conducting photochemical grid model (PGM) modeling to help understand the causes of observed high ozone concentrations in Doña Ana County in southern New Mexico. The SNMOS PGM modeling used a 2011 Comprehensive Air-quality Model with extensions (CAMx) PGM modeling platform that was based on the Western Air Quality Study (WAQS) CAMx 2011b database available through the Intermountain West Data Warehouse (IWDW). Because the WAQS 4 km modeling domain did not extend far enough south to include Doña Ana County, the SNMOS performed WRF meteorological and SMOKE emissions modeling to develop 2011 inputs for a 12/4 km domain centered on Doña Ana County. A CAMx 2011 base case and model performance evaluation was conducted. Emissions were projected to 2025 and CAMx 2025 future year modeling and ozone Design Value projections were performed that showed all sites in Doña Ana County would attain the 2015 0.070 ppm ozone NAAQS by 2025. In addition, ozone source apportionment modeling was conducted for the 2011 and 2025 emission scenarios to quantify the ozone contributions due to source regions (i.e., U.S. states and Mexico) and source sectors (e.g., on-road mobile sources, electrical generating units, etc.) to ozone concentrations in Doña Ana County and vicinity. This webpage presents the SNMOS ozone source apportionment modeling results. More details on the study are provided on the SNMOS project webpage. The SNMOS ozone modeling was conducted by Ramboll Environ and University of North Carolina at Chapel Hill Institute for the Environment (UNC-IE) under contract to the Western States Air Resource Council (WESTAR) as part of the Western Regional Air Partnership (WRAP).

Overview

The SNMOS 2011 and 2025 ozone source apportionment (SA) modeling was conducted using Version 6.2 of the (CAMx) photochemical grid model (PGM). The Ozone Source Apportionment Technology (OSAT) was used for the SNMOS SA modeling. Two SNMOS ozone source apportionment simulations were conducted using the same configuration but using 2011 and 2025 emission scenarios. The SNMOS SA model simulations were conducted following the procedures in the June 15, 2016 SA Modeling Plan and are summarized below. Details on the technical formulation of the CAMx OSAT ozone source apportionment tool is provided in Chapter 7 of the CAMx User’s Guide.

The SNMOS 2011 12/4 km CAMx modeling database was based on the CAMx 2011b 36/12/4 km modeling platform developed by the WAQS and available through the IWDW. Details on the development of the WAQS CAMx 2011b modeling platform, including meteorological modeling and model performance evaluation (MPE), emissions modeling and the CAMx base case modeling and MPE, are available in reports on the IWDW. However, the focus of the SNMOS was on southern New Mexico, as compared to the three-state (CO-UT-WY) region that was the original focus of the WAQS. Thus, SNMOS conducted additional WRF meteorological and SMOKE emissions modeling to develop CAMx 2011 and 2025 inputs for a 12/4 km domain focused on southern New Mexico. Details on the development and results of the SNMOS CAMx 2011 modeling database, including a modeling plan and model performance evaluation, are available on the SNMOS project webpage.

SNMOS Ozone Source Apportionment Modeling Approach

The SNMOS 2011 and 2025 ozone source apportionment simulations were conducted on the 12/4 km domain modeling shown in Figure 1 using Boundary Conditions (BCs) based on CAMx 2011 and 2025 regional model simulations of the continental U.S., respectively. Also shown in Figure 1 are the locations of the ozone monitors (green) and NOx point sources (blue) that include the Carbon coal-fired power plant located in Mexico in the southeast corner of the 12 km modeling domain and the Four Corners and San Juan coal-fired power plants in the northwest corner of New Mexico, as well as numerous compressors in the Permian Basin oil and gas development region just east of the 4 km modeling domain.

Figure 1. SNMOS 12/4 km modeling domains used in the CAMx 2011 and 2025 SA modeling.

The CAMx OSAT ozone SA modelling tools provide separate hourly ozone contributions throughout the 12/4 km modeling domains for each user-selected Source Group. The source apportionment modeling provides a complete accounting of the contributions of all sources, so the Source Groups includes all emission sources. Source Groups are usually defined using a spatial map of geographic area Source Regions and providing as input different Source Categories of emission sectors, the intersection of a Source Region and Source Category defines a Source Group (e.g., on-road mobile source emissions from New Mexico). For the SNMOS CAMx 12/4 km ozone source apportionment simulations, four Source Regions (see Figure 2) and eight Source Categories were defined as follows:

Source Regions (4):

• New Mexico;
• Texas;
• Mexico; and
• Arizona and remainder of other states in the 12 km domain

Source Categories (8):

• Natural (biogenic and lightning NOx);
• On-Road Mobile;
• Non-Road Mobile;
• Oil and Gas (point and non-point);
• Electrical Generating Unit (EGU) Point;
• Non-EGU Point;
• Open Land Fires (wildfire, prescribed burns and agricultural burning); and
• Remainder Anthropogenic.

Initial concentrations (IC) and boundary conditions (BC) are always included as separate Source Groups resulting in a total of 34 Source Groups (34 = 4 x 8 + 2) for the SNMOS source apportionment modelling. Source apportionment simulations were performed with this same configuration for both the 2011 and 2025 emission scenarios.

Figure 2. Four Source Regions used in the SNMOS 2011 and 2025 ozone source apportionment modeling.

SNMOS Source Apportionment Modeling Results

The ozone contributions of each Source Group to the current year (2011) and future year (2025) ozone Design Values and maximum daily 8-hour average (MDA8) ozone concentrations at each monitoring site within Doña Ana County and vicinity (i.e., the 4 km modeling domain) were analyzed several ways:

• Contributions of emissions from each Source Group, Source Region and Source Category to 2011 and 2025 ozone Design Values and MDA8 ozone concentrations.
• Section 179B analysis to assess the contributions of anthropogenic emissions from Mexico to ozone Design Values to demonstrate that “but for” emissions from Mexico Doña Ana County would have attained the October 2015 0.070 ppm ozone NAAQS.
• The source apportionment no Mexico 2011 ozone Design Values were compared to a CAMx no Mexico emissions zero-out sensitivity simulations and found similar contributions to ozone Design Values.
• Sensitivity of 2025 ozone Design Value projections without the influence of fires.

Figure 3. Example SNMOS 2011 SA Vis Tool for Desert View monitor on July 25, 2011 showing Source Region contributions (top pie chart).

Figure 4. Example SNMOS 2011 SA Vis Tool for Desert View monitor on July 25, 2011 showing Source Category contributions (bottom pie chart).

Figure 5. Example SNMOS 2011 SA Vis Tool for Desert View monitor on July 25, 2011 showing Source Category contributions from Mexico (bottom pie chart).