Ambient air quality monitoring in India: NAAQS 2009 and CPCB

What are the NAAQS 2009 standards?

NAAQS 2009 is CPCB Notification No. B-29016/20/90/PCI-L dated 18 November 2009, issued under Section 16(2)(h) of the Air (Prevention and Control of Pollution) Act, 1981. It replaced the earlier standards of 1994 and 1998 and took effect immediately.

The notification has two area categories: "Industrial, Residential, Rural and Other Area", and "Ecologically Sensitive Area (notified by Central Government)". For most pollutants the two limits are the same; they differ only for the annual SO2 and NO2 standards.

Watch the units: CO is in mg/m³, benzo(a)pyrene, arsenic and nickel are in ng/m³, and the rest are in µg/m³.

The notification's footnotes matter as much as the numbers:

• An annual standard is the annual arithmetic mean of at least 104 measurements a year at a site, taken twice a week, 24-hourly, at uniform intervals.
• The 24-hour, 8-hour and 1-hour standards shall be met 98 % of the time in a year. They may be exceeded 2 % of the time, but not on two consecutive days of monitoring.
• When results exceed the limits on two consecutive monitoring days, that is adequate reason to start regular or continuous monitoring and further investigation.

Which ambient air monitoring parameters should a lab measure?

Under CPCB's National Air Quality Monitoring Programme (NAMP), four pollutants are monitored at all locations: SO2, NO2, PM10 and PM2.5. CPCB also records wind speed and direction, relative humidity and temperature, because results mean little without the weather that produced them.

Projects and industries often need more of the 12 NAAQS parameters, such as ozone, CO, ammonia, lead or benzene. The list is set by the consent, the environmental clearance conditions or the customer's monitoring plan. Agree it in writing before the field team leaves.

What is the ambient air quality monitoring frequency under CPCB guidelines?

Under NAMP, CPCB monitors for 24 hours, twice a week, to get 104 observations in a year. Gaseous pollutants are sampled 4-hourly and particulate matter 8-hourly, and PM2.5 is sampled on a 24-hour basis.

This ambient air quality monitoring frequency is what an annual NAAQS comparison needs. A one-off or short campaign can only be compared with the 24-hour, 8-hour or 1-hour standards. Never compare a single 24-hour PM10 result with the annual limit of 60 µg/m³, and never call one result an annual average.

How is PM10 measured by the gravimetric method?

CPCB's Guidelines for the Measurement of Ambient Air Pollutants, Volume I, describe the gravimetric method. Air is drawn through a size-selective inlet and a 20.3 × 25.4 cm glass fibre filter, typically at 1132 L/min. PM10 is the weight gained by the filter divided by the volume of air sampled.

The main steps from the CPCB protocol:

1. Inspect the filter for pinholes and mark its identification number.
2. Condition the filter for 24 hours in a room at 20 to 30 °C and 40 to 50 % relative humidity, or in an airtight desiccator, then weigh it (initial weight).
3. Load the filter, record the flow rate and the elapsed-time meter, and sample, commonly for 8 or 24 hours, reading the flow rate hourly.
4. Remove the filter into a clean envelope or container, and record total time and average flow.
5. Condition the exposed filter again for 24 hours and weigh it (final weight).
6. Calculate the concentration: C (µg/m³) = (Wf − Wi) × 10⁶ / V, with weights in grams and V in m³.

The CPCB protocol cites IS 5182 (Part 23) and calls for periodic calibration of the sampler with an orifice transfer standard. Field and lab blanks belong in your quality control.

Worked example: PM10 from filter weights

Here is a 24-hour run, worked through step by step.

1. Volume of air: V = 1.12 m³/min × 1440 min = 1612.8 m³.
2. Mass collected: 2650.8 − 2512.4 = 138.4 mg = 138,400 µg.
3. Concentration: 138,400 µg / 1612.8 m³ = 85.8 µg/m³, reported as 86 µg/m³.
4. Comparison: 86 µg/m³ is within the 24-hour PM10 limit of 100 µg/m³ for both area categories.

Two unit traps catch new analysts. If weights are entered in grams in a formula that expects milligrams, the result is a thousand times too small and will always "pass". If the flow is in L/min and treated as m³/min, the result is a thousand times too small as well. Write the expected unit beside every input on the worksheet.

Where should an ambient air sampler be sited?

Site the sampler where it represents the area, away from the direct influence of a single source. CPCB's PM2.5 protocol in Volume I gives these siting rules:

• Inlet height 3 to 10 m above ground, at a suitable distance from any direct pollution source, including traffic.
• Distance to an obstacle such as a building more than twice the obstacle's height above the sampler.
• Unrestricted airflow in three of the four quadrants.
• More than 20 m from trees.
• At least 2 m between collocated samplers.

Record the location with coordinates, photographs and a sketch, so that a later campaign can return to the same point.

How should ambient air monitoring results be reported?

A good ambient air report lets the reader check every number against the standard. Include:

• Customer, project and the purpose of monitoring.
• Each location: name, coordinates and area category.
• Start and end date and time, duration, and the averaging time of each result.
• Sampler ID, its calibration status, average flow rate and air volume.
• Filter or absorber IDs and the method for each parameter.
• Weather during sampling.
• Results in NAAQS units, beside the limit for the same averaging time and area category.
• A clear note where a result exceeds a limit, and whether the next monitoring day also exceeded.

For several locations in one campaign, a combined report with parameters against locations is easier to read than one report per filter. See our guide to NABL test report format for the general report requirements.

MoEF&CC recognises environmental laboratories under Sections 12 and 13 of the Environment (Protection) Act, 1986, and customers may also want NABL accreditation for the parameters. Check what the consent or clearance requires before you quote.