Ambient air sampling is a technique of measurement of the concentrations of the air pollutants like SO2, NOx, O3, CO, SPM, RSPM, etc. In addition, it also include measurement of the meteorological parameters such as wind speed, direction, temperature, solar radiation and relative humidity.
There are two types of sampling – continuous and time averaged in-situ sampling. Continuous sampling is carried out by automatic sensors, optical or electrochemical, and spectroscopic methods which produce continuous records of concentration values. The specific time-averaged concentration data can then be obtained from continuous records. Samples are then analyzed by established physical, chemical and biological methods for the concentration values which are the effective average over air sampling includes:
a) Selection of sampling procedures including procedures of analysis of samples.
b) Sampling location
c) Period of sampling, frequency of sampling and duration
d) Auxiliary measurements (including meteorological parameters)
e) Processing of data.
Method of Particulate matter Sampling
Generally there are two methods - (a) Volumetric filtration- sampling a volume of air through a filter medium at a known flow rate for a specified and (b) Gravimetric- by weighing the mass of particles.
Volumetric filtration method
Objective- Sampling of suspended particulate matter in ambient air and the determination of its concentration.
Instruments- High volume sampler with SPM filter Manifold.
Auxiliaries- High volume sampler with airflow manometer for measuring flow rate, microfiber filter (8’’x10’’).
Sampling Location – Sampling station should be located depending upon the objective of measurement campaign and be kept at an altitude depending upon the type of study region (roadways, industrial area, disposal sites, residential tract, etc.). Generally it is kept at a height of about 3 to 10 m from the ground level and sufficiently away from the disturbance or direct obstacle from the source under consideration.
Sampling Frequency – 24 hours at least twice a week making about 104 samples a year.
Procedure of Sampling-
Condition a filter paper in oven
Prepare a sampling assembly by uncorking screws of the bracket
Take the initial weight of the filter paper (Wi, mg)
Place the filter in the sampling system securely and tighten the screws of the bracket
Set the timer for the period of sampling
Start the sampler and adjust flow rate to about 2 litre/min for 24 hours
Note the flow rate at the end of the desired sampling period and stop the sampler
Transit the sampling train to environment laboratory carefully with scientific precautions
Take final weight of the exposed filter with a standard balance (Wf, mg)
Condition the filter paper again for the same period as was done prior to smapling.
Concentration of SPM in μg/m3 = (Wf – Wi)/TVA x10^6
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