Ambient air quality monitoring stations measure real time and peak concentration levels of dangerous pollutants in air.
Industrial and vehicular emissions along with other anthropogenic activities release air pollutants in the atmosphere across Indian cities. It is important to monitor them and keep them under control in order to prevent risk to human health and protect the survival of other living organisms.
Number of AAQM station across India
Centre of Pollution Control Board (CPCB) initiated a nationwide ambient air quality monitoring programme called national air quality monitoring programme (NAQMP) which comprises of 342 monitoring stations all over 127 Indian cities/towns located in 26 states and 4 union territories of the country.
Below are the objectives of the N.A.M.P.
- To determine the current status and trends of ambient air quality
- To examine if the prescribed ambient air quality standards are maintained or not
- To identify the cities that do not abide by the standards
- To gain knowledge and an insight required for developing preventive and corrective measures
- To understand the natural cleansing process undergoing in the environment through various processes such as pollution dilution, dispersion, wind based movement, dry deposition, precipitation and chemical transformation of the pollutants released.
NAQMP focuses on four air pollutants for regular monitoring at all the stations:
- Sulphur dioxide (SO2)
- Nitrogen oxides (NOx)
- Suspended particulate matter (SPM)
- Respirable suspended matter (PM10)
NAQM also considers geographical parameters while conducting measurements such as:
- Wind speed
- Wind direction
- Relative humidity
Ambient air quality monitoring is performed for 24 hours which includes 4 hours of gaseous pollutants sampling and 8 hours of PM sampling, repeated twice a week to yield 104 observations in a year.
Importance of Ambient Air Quality Monitoring stations AAQMS
Ambient air quality monitoring stations help in examining the effectiveness of prescribed standards and assess the quality of life. Depending upon the conditions, measures can be implemented to maintain the ambient air quality standards.
Ambient air quality monitoring stations in a city
The number of stations installed in a city is decided based upon the records of sources of air pollution and emission and the number may vary depending on factors such as the distribution of pollutants, data needed for monitoring, pollutants examined and the area population. In 1977, the World Health Organization (WHO) provided a set of guidelines on the location of monitoring stations.
Parameters influencing site selection for AAQM Station
The parameters influencing site selections for ambient air quality monitoring are sites which indicate possibility or traces of air pollution such as industrial areas, cities and traffic junctions.
Measurements from different cities allow a comparison and help to observe a trend in the patterns of air quality at various metropolitan locations. Factors such as long term site availability, easy access to the site during a year of conducting measurements, sufficient supply of water, electricity and telephone connection, and safe and protected site from adverse weather conditions determine the suitability of a site for the establishment of air quality monitoring stations. Since geographical parameters influence air quality measurements, they are measured during AAQM as well.
Evaluation of air pollutants
Below are the parameters which can be recorded by AAQM station and respective sensor to measure air quality:
- The velocity of air is measured by an anemometer
- Wind direction is measured by wind vane
- Rainfall and precipitation by precipitation gauge or rain gauge
- Temperature by thermometer
- Humidity dry and wet bulb hygrometers
- Humidity of air by sling psychrometers
- Mixing height by SODAR
SO2 and nitrogen dioxide (NO2) are analyzed by wet chemical method which is easy to use in India. High volume sampler is used for measuring particulate matter and respirable particulate matter sample for RSPM in India.
The measurements of ozone, lead, CO are performed by laboratory methods. Field and laboratory measurements are conducted by experts (That’s us!) who ensure maintenance of quality control, and the data collected is handled and analyzed appropriated along with application of corrections wherever necessary.
The data obtained using AAQM stations is utilized by CPCB to examine the nationwide status of air pollutants.
Benefits for AAQM stations
It has been observed that SO2 and NO2 levels in residential areas of all the cities abide by the prescribed National Ambient Air Quality Standards (NAAQS). However, a decreasing trend has been found in the SO2 levels in some cities including Delhi and Lucknow. The RSPM levels have been discovered to exceed the prescribed NAAQS in residential areas of many cities displaying fluctuating trends in the values recorded.
There can be high levels of carbon monoxide (CO) in Delhi due to an increase in the number of vehicles per person, but despite an increase in the vehicular population, CO levels in Delhi have reduced during the past years. This can be attributed to the implementation of measures such as conversion of three wheelers of CNG in Delhi.
Karnataka State Pollution Control Board has installed and commissioned two Continuous Ambient Air Quality Monitoring Stations (CAAQMS), one at City Railway Station, Bangalore and another at Nisarga Bhavan, Saneguruvanahalli in Bangalore. Both the stations operate for 24 hours throughout the year and the data recovered is sent to the CPCB.