Citation:

Fahey, K., R. Gilliam, G. Pouliot, S. Farrell, G. Sarwar, H. Pye, B. Murphy, D. Huff, Nicole Briggs, AND R. Kotchenruther. CMAQ modeling of the 2022 Alaskan Layered Pollution and Chemical Analysis (ALPACA) field study. SIP meeting with AK Dept of Environmental Conservation, Fairbanks North Star Borough, and EPA Region 10, Fairbanks, AK, September 19, 2023.

Impact/Purpose:

PM non-attainment is a serious issue in Fairbanks, Alaska and results from local pollution coupled with weak atmospheric ventilation under conditions of strong temperature inversion. Many knowledge gaps in understanding atmospheric dynamical and chemical processes occurring in the extreme cold and dark conditions encountered in Alaska are further confounded by uncertainties in emission characterization. The Alaskan Layered Pollution and Chemical Analysis (ALPACA) field campaign (Jan-Feb 2022) was a multi-pronged, intensive field campaign focused on better understanding emissions, meteorology, and atmospheric chemistry in Fairbanks and addressing some of the uncertainties in characterizing PM pollution in the region. Post mission analysis of the data collected will greatly benefit from the availability of a modeling platform coinciding with the ALPACA period to elucidate observational data and provide model-based guidance on the types of measurements that could help characterize processes leading to extreme air pollution in the region.  R10 has identified the establishment of a modeling platform for Alaska as a key need for air pollution assessments in the region.  Addressing the knowledge gaps in understanding atmospheric dynamical and chemical processes occurring in the extreme cold and dark conditions encountered in Alaska would also enable improved modeling in other less extreme cold environments.

Description:

·         Fairbanks, Alaska, is in nonattainment of the 24-hour PM2.5 National Ambient Air Quality Standard (NAAQS). Violations of the NAAQS typically occur in winter when the cold conditions are associated with strong temperature inversions and air stagnation, trapping high levels of space heating emissions close to the surface. While PM2.5 in the area is comprised largely of organic carbon from residential wood combustion, the second largest contribution comes from sulfate. Questions surround the formation of secondary sulfate in the cold, dark conditions characteristic of Fairbanks winters when the photoactive oxidants of SO2, dominant under most other conditions, are likely limited.  Recently, the Alaskan Layered Pollution and Chemical Analysis (ALPACA) field study (January 17 – February 25, 2022) brought together several research groups to collect a suite of measurements in and around Fairbanks that, in combination with pre- and post-campaign modeling, targeted a better understanding of the emissions, meteorology, and atmospheric chemistry occurring during Fairbanks winters. For our part, we have developed a modeling platform (including WRF meteorological, SMOKE emissions, and CMAQ air quality modeling) for the ALPACA period. In this talk, I will outline some of the recent advances in simulating sulfur chemistry in the Community Multiscale Air Quality (CMAQ) modeling system and discuss how these updates affect particulate sulfur predictions and how they compare to novel measurements collected during the ALPACA field study.

Record Details: