How we can put ambient air monitoring to good use ?
Ground level concentration can be easily affected if industrial chimneys fails to perform effective plume rise and dispersion.
Why do we conduct ambient air monitoring ? The common practise is to pick parameters from Recommended Malaysia Air Quality Guideline (RMAQG) and evaluate if the ambient air quality either at the periphery of a factory or any sensitive recipient adjacent to the stationary source (factory chimneys). However, what most of the stake holders (factor representatives and testing providers) fail to understand is the relevance between the parameters derived from RMAQG and the activities from the factory. What if the contributor to the parameters tested are from fugitives sources from external factors such as roads or adjacent factories. How does ambient air monitoring results going to assist the factory representative to establish any improvements measures when you cant connect the dot in the very first beginning.
In any monitoring, the objective of the monitoring being carried out must be clearly defined. Ambient air monitoring is ground level concentration testing. However, the ambient air monitoring assessment must clearly define its objective on why it is being conducted. There is no point doing a screening test just to evaluate the quality of air based on the criterion established in RMAQG. There has to be an association of how the industrial activity of any premises may impact the ground level concentration. Prior to establishing any monitoring plans, the industrial premise must identify the emission / discharges of airborne pollutants. These pollutants can be generated and discharged via stationary sources such as chimneys and fugitive sources via dispersion of contamination air from the enclosed building escaping out to the environment.
Once these pollutants are identified, it is good to have a baseline monitoring prior to start any process emitting those identified pollutants. However if it not possible, then. the baseline monitoring can be done simultaneously with other ,monitoring such as stack / chimney emission monitoring and area emission monitoring. The monitoring strategy as such will identify the source of the pollutant, its pollution pathway and the recipient.
Effective plume rise and down wash based on chimney efflux velocity performance.
The functionality of a chimney is to create plume rise for effective dispersion of residual pollutants upon abatement of air cleaning device. A chimney is to generate adequate momentum of vertical discharge (efflux velocity) to enhance the buoyancy of the emission so that plume rise will take place with the interaction of the wind. An effective plume rise will disperse on an elevated plane trailing on horizontal trajectory without reaching ground level while its gets diluted via the dispersion process. However this phenomenon is only sustainable while the efflux velocity of the chimney discharge are maintained high. The drop in efflux velocity way much below than the wind around the tip of the chimney will force the emission downwards around the chimney itself. This short change of path downward is too short distance for any adequate amount of dilution to take place causing the rise in ground level concentration of the specific pollutants discharged from the chimney.
This is why ambient air monitoring can be a very good performance monitoring parameter to be combined with the periodic emission monitoring. In the event of dwindling performance in the efflux velocity due to fan failure, resistance build up or combustion process failure in the aspect of combustion flue gas chimney, the seventy of down wash impact to the ground level concentration must be evaluated for its risk by conducing ambient air monitoring.