EPA releases updated AERMOD

Posted by on Sunday, May 20th, 2018 in Newsletters

What’s Happening Now

EPA News

On April 24, 2018, EPA released an update to the AERMOD system. This includes new versions of AERMOD, AERMAP, and AERMET (all have the version number of 18081). Although the AERMOD update included bug fixes, there were also some interesting enhancements added to the model, which include:

  • The ARM2 capability was extended to buoyant lines sources and source groups that contain buoyant line sources
  • The ALPHA flag for alpha (experimental / research) options was added to AERMOD
  • LOWWIND1, LOWWIND2, and LOWWIND3 options were removed and replaced by a new LOW_WIND ALPHA option
  • The original Ambient Ratio Method (ARM) was removed

Significant Impact Level (SIL) Guidance Finalized – On April 18, EPA released the finalized guidance on SILs for PM2.5 and ozone. In summary, EPA recommends these SILs for NAAQS modeling:

Pollutant and NAAQS NAAQS SIL
8-hour ozone (70 ppb) 1.0 ppb
24-hour PM2.5 (35 µg/m3) 1.2 µg/m3
Annual PM2.5 (12 µg/m3) 0.2 µg/m3

For PM2.5 PSD increment consumption modeling, EPA recommends these SILs:

Averaging period Class I area SIL Class II and III area SIL
24-hour 0.27 µg/m3 1.2 µg/m3
Annual 0.05 µg/m3 0.2 µg/m3

You may download the full guidance here.

2018 Regional, State, and Local Modelers’ Workshop – As we’ve been mentioning the last couple of months, EPA has announced this year’s Regional, State, and Local Modelers’ Workshop (RSL) will be held at the EPA Region I offices in Boston from June 5-7. As usual, the first day of the workshop (June 5) will be open for public attendance. EPA has posted a registration link here.

Otherwise, we are still waiting to hear from EPA on for these upcoming nuggets:

  • EPA’s final Modeled Emission Rates for Precursors (MERP) guidance is due out in 2018
  • EPA’s final ozone / PM2.5 permit modeling guidance should come out in 2018
  • *A new version of AERSURFACE is due out in mid-2018 (maybe in time for the RSL workshop?)*
Conferences and Workshops

Air & Waste Management Association

**New Source Review Workshop Manual** – If you do New Source Review air permitting (and/or modeling), please note that AWMA’s New Source Review Manual is now available! This is an update to EPA’s old 1990 New Source Review Workshop Manual (Draft). This new version is available online in an interactive, hyperlinked and searchable format. It covers all the big NSR-related topics, such as PSD / nonattainment applicability, BACT, air quality analysis, and modeling. Check here for details.

2018 AWMA Annual Conference and Exhibition – It’s time to start thinking about the AWMA’s Annual Conference and Exhibition (ACE)! This year’s premier environmental event will be held in Hartford, CT from June 25-28, 2018. This year’s theme is “Charting the Future – Environment, Energy, and Health”. We’ll be there – will you?

For more information on agenda, registration, etc. go to https://www.awma.org.

Other Conferences

TCEQ 2018 Environmental Trade Fair and Conference – It’s once again time for the Texas Commission on Environmental Quality’s (TCEQ’s) annual Environmental Trade Fair and Conference. It will be held May 15-16, 2018 at the Austin Convention Center. This event, one of the largest of its kind, promises to be full of great presentations on all media – air, water, and waste. We will be there (Exhibit Hall booth 314), and hope to see you there, too! For more information on registration, agenda, and logistics, click here.

If your company, organization, agency, State, etc. has an upcoming modeling or air quality-related event and you’d like it publicized in Providence/Oris Notes, please send that information to us at info@oris-solutions.com, and we’ll be happy to include it.

Simply the Best!


Long-time users of our BEEST software know that when EPA releases new versions of their models and component programs, it means we’ll have a new version of BEEST out soon. So, be on the lookout for BEEST 11.12 later this month!

As always, users in maintenance can download the most recent version of BEEST from www.beeline-software.com | Support | Software Updates.

Beginning with BEEST 11.08, we no longer support Windows Vista.

“Go BEEST Mode!” — What? You still don’t have your own “Go BEEST Mode” t-shirt? We’ve got plenty left, so email your request to info@oris-solutions.com and receive your very own “Go BEEST Mode” T-shirt! You’ll be the envy of modelers everywhere!

AerScreen for Windows

Since AerScreen for Windows uses both AERMOD and AERMAP, we will be releasing a new version of it this month as well.

Users in maintenance can download the most recent version of AerScreen for Windows from www.beeline-software.com | Support | Software Updates.

Beginning with AerScreen for Windows 3.04, we no longer support Windows Vista.

Professional CalPuff

Our most recent version of Professional CalPuff (4.00) was released August 26, 2016 and is available to all registered users with current maintenance.

Users in maintenance can download the most recent version of Professional CalPuff from www.beeline-software.com | Support | Software Updates.

If you have suggestions for an enhancement to any of our modeling software products, please let us know and we’ll do our best to incorporate it into the software ASAP!

Another Testimonial

Westward Environmental, Inc. is a proud and loyal user of the BEEST software package. Our air dispersion modeling team has been using the BEEST front-end system since 2005, and we love it. I dabbled with the Breeze front-end system for a brief time period on one air dispersion modeling project and ended up greatly missing BEEST’s straight-forward easy to use tools so much that I switched back to BEEST mid-project and successfully completed that project on-time. In that same time period agonizing with the Breeze system, I also recognized that Providence-Oris’s technical help was much more friendly, less corporately incentivized and timely in response. I found the technical assistance from the Breeze system to be pushy, impatient and always trying to upsell their products. In contrast, Providence-Oris understands that their roles are to provide timely technical assistance, to educate their clients about their tools and disseminate their turnkey tools without fuss or drama. We can’t say enough positives regarding Providence-Oris’s products and services. We would recommend the BEEST system and Providence-Oris to anyone and all who would approach us regarding their need for a great set of technical tools to accomplish their air dispersion modeling tasks.

David Knollhoff, Westward Environmental

Thank you, David for the kind words!

Modeling Tip of the Month

ARM2 and Source Groups — The Ambient Ratio Method 2 (ARM2) is the new Tier 2 approach for modeling NO2. The science behind it is that the higher the concentration of ambient NOx, the lower the ratio of NO2 to NOx. ARM2 uses this complex equation to determine the ambient ratio due to the NOX concentration from the ALL source group:

y = -1.1723E-17x6 + 4.2795E-14x5 – 5.8345E-11x4 + 3.4555E-08x3 – 5.6062E-06x2 – 2.7383E-03x + 1.2441

where x is the NOx concentration (from ALL) in µg/m3 and y is the calculated ambient ratio.

If you’re using source groups in which they are all concurrent subsets of ALL, everything is fine. However, if you are setting up source groups to determine some optimum worst-case combination of sources – for example, where only 2 out of 3 sources can emit at any given time, then ARM2 will actually yield underpredictions of NO2 for your non-ALL groups. Again, this is because the originally calculated ratio of NO2/NOX was based on the total concentration from ALL, which is greater than any of the subset groups. For example, let’s assume we have three engines at a site, but only two can operate at any one time. So, we might start out with these groups:

ALL: Eng1, Eng2, and Eng3 (ALL is required as a source group for ARM2 to work)
SCEN_A group: Eng1 and Eng2
SCEN_B group: Eng2 and Eng3
SCEN_C group: Eng1 and Eng3

If we input total NOx rates for all engines, we might get these Tier 1 NO2 impacts:

ALL: 415 µg/m3
SCEN_A: 250 µg/m3
SCEN_B: 265 µg/m3
SCEN_C: 240 µg/m3

But if we now remodel using ARM2, AERMOD will calculate the ambient ratio from ALL’s impact and ARM2 equation yields an ambient ratio of 0.35. However, by EPA’s guidance, the minimum ratio is 0.5, so 0.5 will actually be applied to all 4 source groups:

ALL: 415 µg/m3 NOx * 0.5 = 207.5 µg/m3 NO2
SCEN_A: 250 µg/m3 NOx * 0.5 = 125.0 µg/m3 NO2
SCEN_B: 265 µg/m3 NOx * 0.5 = 132.5 µg/m3 NO2
SCEN_C: 240 µg/m3 NOx * 0.5 = 120.0 µg/m3 NO2

However, this is incorrect because AERMOD based the ratio on ALL and applied it to the non-ALL groups. If you went in and modeled each scenario in a separate AERMOD run, where each of them was considered ALL, you’d get these impacts:

SCEN_A (ALL = Eng1 and Eng2): Ambient ratio = 0.56, 250 µg/m3 NOx * 0.56 = 140.0 µg/m3 NO2
SCEN_B (ALL = Eng2 and Eng3): Ambient ratio = 0.53, 265 µg/m3 NOx * 0.53 = 140.45 µg/m3 NO2
SCEN_C (ALL = Eng1 and Eng3): Ambient ratio = 0.58, 240 µg/m3 NOx * 0.58 = 139.2 µg/m3 NO2

So, as you can see, when doing any kind of a scoping study or when trying to determine what your worst case scenario is, keep in mind that AERMOD bases the ambient ratio on ALL, and you can potentially underestimate NO2 impacts.

**Keep watching this newsletter and our website in 2018 for something brand new that will make modeling even easier.**

“Our expertise is contagious. Catch it!”

AERMOD Modeling for Permits

Our next AERMOD Modeling for Permits class will be July 31-August 1. As usual, it will be at our training facility at our Austin, Texas office. Register today and plan to join us in the Live Music Capital of the World! Click here to register!

Advanced AERMOD

Our next Advanced AERMOD class is going to be August 2-3, also at our Austin office. This popular course covers those topics that are near and dear to modelers, such as:

  • NAAQS modeling for 1-hour NO2, 1-hour SO2 and 24-hour PM2.5 (including the new MaxDCont Viewer)
  • Meteorological data processing with AERMET / AERMINUTE / AERSURFACE
  • Changes related to the new Appendix W (Guideline on Air Quality Models)
  • MAXIFILE and ARRAY2 processing
  • AERMOD beta options, such as PSDCREDIT

So, get your “Keep Austin Weird” vibe on and join us by registering for Advanced AERMOD by going here.

2018 Class Schedule

Here’s the last of our AERMOD classes for 2018:

Class Dates Location
AERMOD Modeling for Permits November 13-14 Austin, TX
Advanced AERMOD November 15-16 Austin, TX

**Don’t forget, if our schedule of classes doesn’t mesh with your schedule, or if you have several people that need to be trained at once, contact us about setting up an on-site class. Have laptop, will travel!**


BeestXpress users now have some great new enhancements to work with:

  • The “Job Details” webpage now displays the pollutant being modeled;
  • The “Job Details” webpage now displays run progress for MAXDCONT calculations;
  • Modeling runs with multiple partitions now include a combined AERMOD input file (*.DTA) in the output .ZIP file;
  • Added an option to the “Submit Job” webpage that affects modeling runs with multiple partitions: the intermediate output files created by each partition can be omitted from the output .ZIP file
  • The “Job Search” webpage now includes the option to search by project number
  • Users have access to up to 50 partitions per AERMOD run

We’re also excited to note the BeestXpress has now processed over 300,000 AERMOD runs. Wow!

If you’ve never used BeestXpress, or it has been a while since you did, you may want to log on at www.beestxpress.com to take advantage of our AERMOD “force multiplier”. That AERMOD run that might have taken a day to run on your desktop computer can finish in an hour or less on BeestXpress. When time is money, BeestXpress is the best modeling return on investment there is!

Meteorological Data Processing Services

Do you need AERMOD-ready or CalPuff-ready meteorological data? If so, we can help! Whether it’s running the AERMET / AERMINUTE system or a full CalMet run, Providence/Oris has the background, know-how, and experience to have your data processed and ready for you ASAP. Need on-site data processed? We do that, too! If you’d like more information, contact us at info@oris-solutions.com or jamesred@providenceeng.com.

Consulting Solutions

One thing that we’re very proud of is the depth and range of our modeling experience and expertise. The last time we counted, it was somewhere in the neighborhood of 250 years’ worth of experience. The kinds of models we’ve used include all types, ranging from simple screening tools like SCREEN and AERSCREEN to plume models like ISC and AERMOD to CalPuff to CAMx. The types of analyses included basic Significant Impact Level, NAAQS, PSD increment consumption, Class I analyses, air toxics, and SIP attainment demonstrations. Most recently, we have begun conducting nonattainment permit inter-pollutant trading (NOx for VOC) modeling using CAMx. So, we’ve seen it all. To that end, should you or your clients need additional modeling assistance or just a second set of eyes to QA or peer review your modeling (ranging from initial protocol up to final submission), we stand ready to help. Feel free to contact us at (512) 258-8855 or info@oris-solutions.com.



May 15-16, 2018
TCEQ Environmental Trade Fair
Austin, TX

June 5-7, 2018
EPA Regional, State, and Local Modelers’ Workshop
Boston, MA

June 25-28, 2018
AWMA 111th Annual Conference and Exhibition
Hartford, CT

July 31-August 1, 2018
AERMOD Modeling for Permits
Austin, TX

August 2-3, 2018
Advanced AERMOD
Austin, TX