It is widely recognised that background biological and chemical materials and their continuous environmental fluctuation will significantly influence monitoring. Air movement, sunlight/UV radiation, humidity, rainfall, and inversions are some of the environmental factors that need to be considered during monitoring. Another consideration is where and when to sample with regard to spatial and temporal relevance [19] . For example, the release of pathogens can cause a significant downwind hazard which requires a wide area and long period of sampling [7] .