This report shows how EPA took a closer look at air quality data after the Hazelwood mine fire was over in order to develop a better understanding of the scientific correction factor that needs to be applied to rapid-response monitoring. Early in responding to the fire, EPA was collecting data using portable instruments. These instruments give us a rapid indication of air quality, but we need to apply a scientific correction to the data. The corrected data gives us a more accurate estimate of air quality, which has been published it in this report. Understanding these corrections is important for future use of rapid air monitoring in Victoria.