The Importance of Monitoring Volatile Organic Compounds (VOCs) in Air Quality Determination

Poor urban air quality accounts for 7 million deaths per year, according to the World Health Organization. Unless poor air quality can be addressed, death rates will continue to rise.

Photochemical and sulfurous smog not only differ in composition but are also distinct in regard to the weather conditions that give rise to them. Photochemical smog emerges in hot, sunny conditions and typically peaks in the afternoon.

Sulfurous smog occurs in cold, damp atmospheres, peaking at dawn. The wind may also carry pollution into a city, in particular the smoke generated from power station emissions and the burning of vegetation.

Clean Air

The Earth’s atmosphere is diverse. Biological, physical and chemical processes are all part of ‘clean air’, a gas mix that is free of toxic gases and particulates – it is exceptionally well-balanced for supporting planetary life.

Except for halocarbons and a number of inert gases, the concentration of gases in the atmosphere remains in constant flux and is actively mediated by living processes.

The mix of gases in clean air is generally at an optimal level for life. Oxygen is balanced at a concentration that allows aerobic organisms, such as humans, to breathe easily, whilst not too high as to result in inextinguishable forest fires.

Carbon dioxide is abundant enough to support plant growth, both as a source of carbon and in preserving sufficient warmth from the sun. Essential elements of life, including sulfur and iodine, are carried from land to sea in the form of volatile organic compounds (VOCs).

Several gases, which are toxic and dangerous to existence are extracted by chemical and physical adsorption on solid particles (particulates), which eventually fall out of the air under gravity as rain or dust.

Moreover, a series of chemical reactions, including reactions with sunlight (photochemical reactions), maintain an atmosphere that is almost entirely free of specific VOCs released by plants; it would seem to their own and wider benefit.

For instance, recently, it was established that when bruised, leaves release pheromones (VOC messengers) that attract predators of leaf-eating insects.

The Importance of Monitoring Volatile Organic Compounds (VOCs) in Air Quality Determination

Image Credit: Ion Science

“Photochemical smog is a major environmental pollution culprit, produced when sunlight reacts with nitrogen oxides (NOX) and at least one volatile organic compound (VOC) in the atmosphere.”

Human Impact on Air Quality

Gases and particulates emerging as a result of human activity encounter the exact same processes as those naturally occurring: being either photochemically oxidized and/or in condensing and forming on particulates which eventually fall out as dust or rain.

However, the sheer amount of ‘primary pollutants’ emitted by human activity can be hazardous, as well as producing ‘secondary pollutants’ through a number of different reactions.

Additionally, when high concentrations of VOCs, for example, are released into the air, they can ‘overwhelm’ the very low concentrations of extremely reactive atmospheric cleansing agents, including OH and NO3, meaning that they remain unchanged for prolonged periods of time.

Primary pollutants that are released directly into the atmosphere, include:

  • CO from vehicle exhaust, wood and coal burning.
  • NO and NO2 (‘NOx’), chiefly from vehicle exhaust and coal fired power stations.
  • SO2 and SO3 (‘SOx’) primarily from sulfurous coal burning stoves and power stations.
  • VOCs apart from methane from the following sources:
    • Unburnt hydrocarbons from vehicles - This pollutant is eradicated where legislation controls catalytic conversion of unburnt hydrocarbons.
    • Solvent release and spills - These can occur as a result of badly managed industrial plant processes, fugitive emissions and spillages, but also as a distinguishing feature of urban pollution due to volatilization of solvents in domestic products, such as cleaners and polishes.
    • Terpenes from forest fires. 

Secondary pollutants, resulting from action of sunlight on NOx and VOCs, are: 

  • Aldehydes such as formaldehyde, a harmful biocide.
  • Ozone, O3, which in the lower atmosphere is extremely hazardous to all lifeforms.
  • Acid rain is a secondary pollutant, formed by the reaction of rain droplets with NOx and SOx
  • A resultant photochemical or ‘Los Angeles’ smog made up of particulates often containing metal oxides, nitric acid, PAN, dissolved VOC’s and SVOC’s.
  • Peroxyacyl nitrates (PANs).
  • Sulfurous or London smog, formed from sulfurous coal burning, made up of water, ash, PAH’s, sulfuric acid and nitric acid.

The Importance of Monitoring Volatile Organic Compounds (VOCs) in Air Quality Determination

Image Credit: Ion Science

Monitoring VOCs of Urban Air Quality 

10.0 eV VOC Gas Sensor

The Importance of Monitoring Volatile Organic Compounds (VOCs) in Air Quality Determination

Image Credit: Ion Science

Range: 0 to >100 ppm. Minimum detection limit: 5 ppb. 10.0 eV lamp. 

The 10.0 eV VOC gas sensor - MiniPID 2 is utilized for the improved selectivity of compounds with lower ionization energies. 

11.7 eV VOC Gas Sensor

The Importance of Monitoring Volatile Organic Compounds (VOCs) in Air Quality Determination

Image Credit: Ion Science

Range: 0 to >100 ppm. Minimum detection limit: 100 ppb. 11.7 eV lamp. 

The 11.7 eV VOC gas sensor lamp expands the range of detectable compounds, exclusively available via ION Science. 

High Sensitivity VOC Gas Sensor

The Importance of Monitoring Volatile Organic Compounds (VOCs) in Air Quality Determination

Image Credit: Ion Science

Range: 0 to 3 ppm. Minimum detection limit: 0.5 ppb. 10.6 eV lamp. 

The high sensitivity VOC gas sensor possesses the highest sensitivity VOC gas sensor. It is ideal for sub-PPB level detection. 

PPB VOC Gas Sensor

The Importance of Monitoring Volatile Organic Compounds (VOCs) in Air Quality Determination

Image Credit: Ion Science

Range: 0 to >40 ppm. Minimum detection limit: 1 ppb. 10.6 eV lamp. 

The PPB VOC gas sensor - MiniPID 2 is optimized to offer an exceedingly low background which enables optimum low-end sensitivity. 

PPB WR VOC Gas Sensor

The Importance of Monitoring Volatile Organic Compounds (VOCs) in Air Quality Determination

Image Credit: Ion Science

Range: >200 ppm. Minimum detection limit: 20 ppb. 

The MiniPID 2 PPB Wide Range VOC gas sensor is optimized to produce an exceptionally low background which facilitates optimum low-end sensitivity. 

PPM VOC Gas Sensor

The Importance of Monitoring Volatile Organic Compounds (VOCs) in Air Quality Determination

Image Credit: Ion Science

Range: 0 to 4000 ppm. Minimum detection limit: 100 ppb. 10.6 eV lamp. 

The PPM VOC gas sensor - MiniPID 2 was developed for detecting VOCs across the widest dynamic range on the market without jeopardizing performance. 

PPM WR VOC Gas Sensor

The Importance of Monitoring Volatile Organic Compounds (VOCs) in Air Quality Determination

Image Credit: Ion Science

Range: >10,000 ppm. Minimum detection limit: 500 ppb. 10.6 eV lamp. 

The MiniPID PPM WR VOC gas sensor has been developed for detecting VOCs over the widest dynamic range on the market without jeopardizing performance. 

Sensor Development Kit (SDK)

The Importance of Monitoring Volatile Organic Compounds (VOCs) in Air Quality Determination

Image Credit: Ion Science

Sensor Development Kit (SDK) for incorporating the MiniPID 2 photoionization sensor.

This information has been sourced, reviewed and adapted from materials provided by Ion Science.

For more information on this source, please visit Ion Science.

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