Abstract: The six criteria air pollutants of PM2.5, PM10, NO2, SO2, O3 and CO, as designated by the United States Environmental Protection Agency's National Ambient Air Quality Standards, were sampled with portable sensors three times weekly over a period of three months at five locations to determine a relationship between the indoor and outdoor air quality in the Greater Milwaukee Area. Data were catalogued, graphed, and processed through a regression analysis. After the analysis, data with an R2 value of 0.4 or higher were considered as designating a significant relationship. Therefore, between indoor and outdoor air pollution, data only showed PM2.5 to have a statistically important relationship; PM10 and NO2 had statistically non-important relationships; and SO2, O3, and CO had inconclusive relationships. After considering factors not addressed by this study, companies wishing to improve indoor air quality may wish to utilize a higher MERV rated filter to address PM2.5 and PM10; and employ NO2 and/or SO2 sensors to monitor levels of these gases. These gases were singled out as SO2 was the only pollutant to exceed any NAAQS recommended levels indoor and NO2 was nearly exceeding recommended levels.