Aerosol forecast by Eta-CMAQ for the poor air quality episode in early February 2005

Many air pollution agencies in the Upper Mid West and the Great Lakes regions had issued air advisories between January 31st and February 4th 2005. Air Quality Index (AQI) issued on the EPA web site in Minnesota peaked at 155 on January 31st. In the Chicago area, AQI measured between 110 and 140 for most of this first week of February. The deterioration of the air quality over these regions for a rather prolonged duration had been attributed to the slow passing of a large high pressure system centered over the Great Lakes during the period. The pressure system was accompanied by extensive cloudiness and snow coverage over the same regions. This combination of meteorological conditions resulted in reduced atmospheric mixing; and high rate of atmospheric particle formation and growth due to high RH in the lower levels. In this study, the National Weather Service's (NWS) Eta-CMAQ Air Quality Forecast System (AQFS) has been used in the research mode to predict the Particulate Matter (PM) concentration and the speciation of this poor air episode. The model result has been first grossly verified favorably by comparing its Aerosol Optical Depth (AOD) and fine particles with diameter less than 2.5 μm (PM2.5) concentration predictions with the observed values by the Aerometric Information Retrieval Now (AIRNOW) network. Speciation analyses of the model results shows that nitrate and anthropogenic organic particles formed the bulk of the particulate matter for most of the time for the high AQI locations and durations. Temporal variation of the speciation analyses have also been done in the study.