Ambient Air Testing

Ambient air is atmospheric air in its natural state. It is what we breathe in when the atmosphere is not contaminated by air-borne pollutants. Ambient air is vital to the survival of humans and animals. The composition of ambient air varies depending on the elevation above sea level as well as human factors such as the level of pollution. The ambient air quality, therefore, is directly affected by the activities of people.

The World Health Organization estimates that globally 1 in 8 deaths (approximately 7 million people in 2012) are attributable to ambient air pollution, of which over half are due to outdoor pollutants (both urban and rural). 92% of the world's population live in areas where air quality fails to meet WHO targets and it is estimated that outdoor particulate air pollution is responsible for the loss of 69.7 million disability-adjusted life years worldwide. Recent Supreme Court cases in the United States of America and the United Kingdom, have increased public awareness of polluted air. Google news returns for "air pollution" have increased by a factor of 919 between 2006 and 2016 (in comparison, returns for "cystic fibrosis" have increased by a factor of 298). Air pollution is associated with a host of communicable and non-communicable diseases including pneumonia, cancer, asthma, stroke and heart disease, diabetes and dementia, although evidence for the strength of these associations varies.

Fig. 1 The effect of ambient air pollution on birth weight

The two major goals of testing for air pollutants are identification and quantification of a sample of ambient air. Air pollution measurement techniques generally pass through evolutionary stages. The first is the qualitative identification stage. This is followed by separate collection and quantification stages. The last stage is the concurrent collection and quantification of a given pollutant.

Taking gaseous SO₂ as an example. The presence of SO₂ in ambient air can be detected by exposing a lead peroxide candle for a period of time and then measuring the amount of lead sulfate formed. Because the volume of air in contact with the candle was not measured, the technique could not quantify the amount of SO₂ per unit volume of air.

The next stage involved passing a known volume of ambient air through an absorbing solution in a container in the field and then returning this container to the laboratory for a quantitative determination of the amount of absorbed SO₂. The United Nations Environmental Program–World Health Organization's worldwide air sampling and analysis network used this method for SO₂, the only gaseous pollutant measured by the network. The final evolutionary step has been the concurrent collection and quantification of SO₂. An example of this is the flame photometric SO₂ analyzer, in which SO₂-laden air is fed into an H2 flame, and light emissions from electronically excited combustion products are detected by a photomultiplier tube. Prior calibration of the analyzer permits the rapid determination of SO₂. This is but one of the many methods available for the measurement of SO₂.

Hundreds of chemical species are present in urban atmospheres. The gaseous air pollutants most commonly monitored are CO, O₃, NO₂, SO₂, and nonmethane volatile organic compounds (NMVOCs). Measurement of specific hydrocarbon compounds is becoming routine in the United States for two reasons: (1) their potential role as air toxics and (2) the need for detailed hydrocarbon data for control of urban ozone concentrations. Hydrochloric acid (HCl), ammonia (NH3), and hydrogen fluoride (HF) are occasionally measured. Calibration standards and procedures are available for all of these analytic techniques, ensuring the quality of the analytical results. The following pictures show some detective principles of ambient air pollutants.

Fig. 2 Calibration apparatus for ozone analyzer (UV) (Vallero, D. A 2008) Fig. 3 Schematic diagram of chemiluminescent detector for NO₂ and NO. PMT: photomultiplier tube (Vallero, D. A 2008) Fig.4 NDIR analyzer (Vallero, D. A 2008)

Alfa Chemistry is professional in ambient air testing and we can provide accurate and reliable tests results within the time constraint. Please feel free to contact us if you have any concern or would like us to perform any ambient air testing. Check our instruments list to see our capabilities.

Reference

• Vallero, D. A. (2008). 17 – ambient air pollutants: analysis and measurement. Fundamentals of Air Pollution, 106(3), 472-499.