Air-quality forecasting for the Pacific Northwest

AIRPACT

Introduction to AIRPACT

What is AIRPACT

What is AIRPACT?

AIRPACT is a computerized system for predicting air quality (AQ) for the immediate future of one to three days for ID, OR and WA. AIRPACT predicts air quality by calculating the chemistry and physics of air pollutants as determined by pollutant emissions within the context of the background, natural air chemistry and predicted meteorology. Meteorology has a first order effect on air pollution, with variables such as wind speed, temperature and precipitation affecting dilution, chemical reaction rates and the removal of pollutants through rain-out, respectively.

AIRPACT cloud cover
AIRPACT cloud cover

Pollutant emissions are another first order determinate of air quality, along with meteorology, and are calculated referring to detailed spatial databases of land use, traffic volumes, industrial emissions and natural emissions from vegetation and soils, all adjusted as appropriate by date, time of day and predicted temperature and solar (uv) light intensity. AIRPACT's project name, the Air Information Report for Public Access and Community Tracking, reflects the goal of bringing meaningful information on the quality of the air (or the level of air pollutants) to the public from a variety of sources, including both model results and monitoring stations.

What is air quality

What is Air Quality?

Air quality refers to the extent that air pollution has degraded our air, both in terms of human health risk from breathing air pollutants and in terms of other non-health effects such as visibility and scenic value. Air quality is generally evaluated in terms of criteria pollutants, which are gaseous and particulate contaminants regulated under the Clean Air Act and amendments thereof. Of primary concern in our region are the following gas phase chemicals:

  • O3, ozone
  • NOx, nitrogen oxides NO and NO2
  • CO, carbon monoxide,

and the primary particulates of concern:

  • PM2.5, particles of solid and/or liquid with D < 2.5 micron (Ám), and
  • PM10, particles of solid and/or liquid with D < 10 micron (Ám).

What should I look at

What should I look at?

AIRPACT results are presented on a daily basis under date-named folders, shown in a 'latest on top' order. A daily forecast result is shown as columns of links for Meteorology, Emissions, CMAQ results, and Statistics. Regionally, the critical pollutants are found as O3 (ozone) and PM2.5 under the CMAQ results column. Emissions, CMAQ results and statistics links are also organized into 'gas phase' and 'particulate' groups. Most of the links (except for the elevation and land-use links under Meteorology and the Statistics) run animations, with the user given control via widgets in the left hand frame. Times are given on the images for the hour of the result and the time stamp in the upper frame indicates both the UTZ and interpreted time. Time stamps are for the model's instantaneous emissions rate or mixing ratio; the results are not hourly averages.

Links to explore in the AIRPACT simulation data table (shown here for the current simulation):

  • Meteorology links show how temperature, winds (UVW) and mixing height (PBL) vary throughout the forecast period.
  • Emissions show calculated release rates (combined from all sources).
  • CMAQ results links show hourly forecast results as animations.
  • Daily and monthly spatial patterns and monthly maxima are under Statistics.


A complete list of graphics products used to evaluate AIRPACT performance can be found HERE.

How does it work

How does it work?

AIRPACT uses an EPA developed model called the Community Model for Air Quality (CMAQ) that calculates air quality for a region by treating the region as a three-dimensional grid of cells of regular size. Thus, AIRPACT treats the Northwest region as a gridded volume of 95 cells by 95 cells, in 21 vertical layers. The cells are 12 km in N-S and E-W extents but the vertical level depth varies with elevation. The problem of predicting the region's air quality thus becomes the problem of computing the air quality for a volume of air contained within a model grid cell volume, many times over. For each grid cell volume, air quality is solved by calculating changes in air chemistry from the beginning of a time step (say t=0) until the end of that step (t=1) accounting for the contribution of several different factors for each chemical and particulate of concern:

  • Emissions of fresh pollutant into the cell volume
  • Creation and destruction of molecules by chemical reactions
  • Growth or shrinkage of particles by physical and chemical reactions
  • Transport into and out of the cell across N, S, E and W cell walls by wind
  • Transport across top and bottom walls (cell floor and ceiling) by vertical mixing
  • Removal by deposition to land or water surfaces or by precipitation


Thus, treating each grid cell in turn, marching forward in time allows for the calculation of air quality hour by hour.

Who is involved

Who is involved?

Federal, state, local and tribal AQ authorities jointly strive to protect human health and other values by protecting air quality; AIRPACT has been developed with support, guidance and cooperation from US EPA Region 10, the WA Department of Ecology, the Oregon Department of Environmental Quality and the Idaho Department of Environmental Quality, and the Puget Sound Clean Air Agency, among others.

For more information, contact:

Civil & Environmental Engineering, PO Box 642910, Washington State University, Pullman WA 99164-2910, 509-335-2576