The Hybrid Single Particle Lagrangian Integrated Trajectory Model (HYSPLIT) is a computer model that is used to compute air parcel trajectories and deposition or dispersion of atmospheric pollutants. It was developed by NOAA and Australia's Bureau of Meteorology.
One popular use of HYSPLIT is to establish whether high levels of air pollution at one location are caused by transport of air contaminants from another location. HYSPLIT's back trajectories, combined with satellite images (for example, from NASA's MODIS satellites), can provide insight into whether high air pollution levels are caused by local air pollution sources or whether an air pollution problem was blown in on the wind.
HYSPLIT is rather unusual in that it may be run in client-server mode (HYSPLIT-WEB) from the NOAA website, allowing members of the public to select gridded historical or forecast datasets, to configure model runs, and retrieve model results with a web browser.
Example of use
Most air pollution in Door County, Wisconsin comes outside the county. This map shows how air travels to the pollution monitor in Newport State Park. Because the monitor at Newport State park is near the shore, only the red lines (which show the lower air currents) meaningfully depict the path of ozone to the monitor. Unfortunately, as shown on the map, these lower air currents carry polluted air from major urban areas. But further inland, the air from higher up mixes more, so all color lines are significant when tracing the path of air pollution further inland. Fortunately, these higher air currents (shown in green and blue) blow in from cleaner, mostly rural areas.
- Photo of the monitoring station on page 128 of WI DNR. "Air Monitoring Network Plan 2016 June 2015" (PDF). EPA. Retrieved 6 February 2019.
- US EPA. "Wisconsin: Northern Milwaukee/Ozaukee Shoreline Area, Sheboygan County Area, Manitowoc County Area, Door County Area Final Area Designations for the 2015 Ozone National Ambient Air Quality Standards Technical Support Document (TSD)" (PDF). Green Book. Retrieved 7 February 2019.