Outdoor air quality monitoring is the process of taking a systematic and long-term assessment of pollutant levels by measuring the quantity and types of various pollutants in the surrounding environment.
Outdoor is often referred to as ambient air. Some of the common sources of outdoor air pollution are emissions caused by combustion processes such as motor vehicle emissions, solid fuel burning, and industrial activities.
While some natural forces can also trigger pollution such as ash from a volcanic eruption, smoke from wildfires, and emission from vegetation. Most common outdoor air pollutants of include Ozone (O3), Nitrogen dioxide (NO2), Carbon monoxide (CO), Sulphur dioxide (SO2), particulate matter (PM2.5, PM 1, AND PM10)
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Outdoor Air Quality Monitoring Devices
Outdoor or ambient air quality devices are equipment used in the collection and assessment of air pollutants in the environment to determine the concentration level of the individual gases found in the environment. Direct-reading air quality instruments or monitors provide information at the time of sampling, enabling rapid decision-making.
These instruments provide the trained and experienced user the capability to determine if site personnel are exposed to airborne concentrations which exceed instantaneous exposure limits for specific hazardous air contaminants.
Air quality monitors can be useful in identifying oxygen-deficient or oxygen-enriched atmospheres, which can be dangerous to life or health conditions, increased levels of airborne pollutants, flammable atmospheres, and radioactive hazards.
Direct reading instruments are particularly useful for identifying point source contamination or emissions such as gas leaks. Periodic monitoring of airborne levels with a real-time monitor is often critical, especially before and during work activities.
The list below are some outdoor air quality monitor devices
- Photo Ionization Detectors
- Single Gas Monitors and Tube
- Multi-Gas Hand Held Monitor
- Flame Ionization Detection
- Particulate Matter Monitor
- Air Velocity
- Landfill Gas Monitor
- Gas Leak Detectors
- Multi-Gas Monitor with Photo Ionization Detector
1. Photo Ionization Detectors
Photo Ionization Detectors make use of a fan or a pump to attract air into the instrument’s detector. A high-energy ultraviolet (UV) light source ionize the chemicals in the air stream.
The charged molecules are collected on a charged surface, which generates a current that is directly proportional to the concentration of the chemical in the air being sampled.
The ionization potential (IP) describes the amount of energy needed to induce ionization in a particular chemical. Photo Ionization Detectors are used for, Site characterization, Exposure monitoring, etc.
2. Single Gas Monitors and Tube
Single gas and monitor tubes are devices that can monitor carbon dioxide, carbon monoxide, hydrogen sulfide, and a variety of additional toxic gases. Whose sample concentration is shown in parts per million(ppm), percent oxygen, or percent LEL (Lower Explosive Limit).
3. Multi Gas Hand Held Monitor
Multi-gas monitors incorporate separate sensors for oxygen, combustible atmosphere, and up to three toxic gases in the same handheld monitor. These monitors may function in active mode or in passive mode, where a pump module is used to attract air across the sensors.
In an oxygen-deficient atmosphere, many flammable gas sensors do not provide reliable readings. Therefore, oxygen content must always be checked before taking combustible gas readings. Flammable gases and vapors are tested second for fire or explosion risk. Monitoring for toxicity is conducted last.
4. Flame Ionization Detection
This device makes use of flame to dissociate airborne pollutants. Once they are been dissociated, then they can be detected and measured.
Flame Ionization Detectors are the most sensitive for saturated hydrocarbons (alkanes), and unsaturated hydrocarbons (alkenes and alkynes).
5. Particulate Matter Monitor
This instrument is used to monitor particulate matter such as dust, smoke, mists, and fumes. They can be used for monitoring the respirable fraction of dust, and are small enough to use for personal exposure monitoring.
In the monitor, aerosol photometers operate by detecting scattered light. The amount of light reaching the detector is proportional to the number of particles passing through the detection chamber which is known as nephelometers.
6. Air Velocity
Velocity meters (hot wire anemometers) are handheld devices with an extendable narrow rod used to measure air speed (velocity). They can be used to monitor the effectiveness of ventilation systems and local exhaust systems.
7. Landfill Gas Monitor
Specialized landfill gas (LFG) systems are used to extract, collect and control gas migration and surface emissions. Landfill gas field monitoring is important for the safe and successful operation of Landfill gas systems as there is a need for a routine check on emissions from the landfill site.
8. Gas Leak Detectors
Gas leak detectors are handheld device devices for the gas check. They provide stable, repeatable readings of multiple gases and gas mixtures. This shows an advanced micro thermal conductivity sensor, Gas check effectively detects many gases in ultra-low concentrations.
- They are available in four models; G1, G2, G3, and Tesla
- They are Fast, accurate leak detection
- They are Simple handed operation
- They are particularly sensitive to ammonia, argon, butane, helium, hydrogen, and SF6
- They have auto ambient air calibration
9. Multi-Gas Monitor with Photo Ionization Detector
Multi-gas monitors incorporate separate sensors for oxygen, combustible atmosphere, and up to three toxic gases in the same handheld monitor. The sample concentration is displayed in ppm, percent oxygen, or percent LEL (Lower Explosive Limit), as applicable.
How Do You Measure Outdoor (Ambient) Air Quality
Outdoor air quality can be measured using an electric monitor that consistently tests and reports the levels of pollutants and humidity through an in-built display panel.
It can also be measured using an air quality index which works like a thermometer that runs from 0o to 500o. The air quality index helps to indicate changes in the amount of pollution in the air. However, there are specific methods implored for the measurement of ambient air quality which includes:
- Passive Monitoring
- Active (Semi-Automatic) Sampling
- Automatic Point Monitoring
- Use of Photo-chemical and Optical Sensor Systems
- Remote Optical or Long-Path Monitoring
i. Passive Monitoring
In the passive monitoring method, the diffusion tubes absorb a specific pollutant from the ambient air. The tubes with the air pollutants content are sent to a laboratory where proper analysis is conducted to see how much pollution will be detected. The diffusion tubes normally monitor for 2-4 weeks at a time and no power supply is needed for this process.
ii. Active (Semi-Automatic) Sampling
This is done with the use of an analyzer. The analyzer absorbs the ambient air through a filter for a set period for example one filter per day or more per day. The filters which are used to obtain the air content are transported to a laboratory for analysis to detect the level of air pollution in that environment.
iii. Automatic Point Monitoring
This is done with the use analyzer also but it is slightly different from active sampling. In automatic sampling, the analyzer pulls the ambient air however only the specific gas that is to be measured is obtained and its concentration is determined. Automatic point monitors pollutants for 24 hours a day The Data obtained from the site of study is sent directly to your computer which makes it accessible instantly by anyone.
iv. Use of Photo-chemical and Optical Sensor Systems
These are portable monitoring tools that can continuously monitor a range of pollutants. The sensors are of low sensitivity and are mostly suitable for identifying hotpots at roadsides and near point sources.
Data can be downloaded to your computer and analyzed.
v. Remote Optical or Long-Path Monitoring
In this method of sampling, pollution is detected between a light source and a detector which are placed separately at a site. Without delay, measurements can be taken with this type of sampling. Data can be sent from the analyzer directly to your computer which means it can also be seen instantly
Globally, there is an increasing awareness of environmental health, and the quality of the air we breathe. This awareness has put pressure on those generating pollutants, like fugitive emissions, to increase their monitoring, control, and reporting activities. Fugitive emissions such as road construction dust, release from vents, stacks, chimneys, vehicular emissions, and industrial emissions impact outdoor air quality.
Therefore outdoor air quality monitoring is an important environmental exercise that has to be conducted on a daily down to hourly basis, to ascertain ambient air pollution levels in a region. The information obtained will show the status of the air quality we breathe.
However, while air quality monitoring itself does not reduce the pollution rate of the atmosphere, but then, it provides us with adequate information on the abundance of the pollution, where the pollution is, and when the pollution occurred.
With this also, a conclusion can be drawn on the level of success made in reducing air pollution with the aid of the data obtained, and at the level at which it has been reduced. And if need be suggest aggressive measures to be put in place to achieve more results.
Outdoor Air Quality Monitoring – FAQs
Do air quality monitors actually work?
Air quality monitors are great tool that ensures that the air we are breathing is safe. As 70%-85% according to the research of the obtained air quality result from air quality monitoring are highly accurate and reliable. They are helpful and beyond contradiction of very great advantage to human health, because having the proper knowledge of the ambient air will help in enacting measures to address human attitudes in the environment concerning air pollution
What is the best outdoor air quality monitor?
There are varieties of outdoor air quality devices which vary from city to city, which means that the best quality of ambient air monitor is dependent on the regions air quality standard as decided by the environmental protection agencies.
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Ahamefula Ascension is a Real Estate Consultant, Data Analyst, and Content writer. He is the founder of Hope Ablaze Foundation and a Graduate of Environmental Management in one of the prestigious colleges in the country. He is obsessed with Reading, Research and Writing.