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Palliser Airshed Society

Data Collection

Passive vs. Continuous Sampling
Passive Monitoring

Passive sampling devices can monitor air pollutants without the need for electricity, data loggers or pumps. Passive sampling devices are lightweight, portable and relatively simple to operate. No active movement of air through the sampler is necessary. A major advantage of using a passive sampling system is that a network of multiple samplers can be used over a large area to determine the spatial variation of pollutant levels. Passive samplers are also useful for looking at long-term trends of air pollutants at specific locations. However, since sampling is conducted over a period of about one month, events that last for a short time period, such as one hour, may be "averaged out".

Continuous Monitoring Station

Continuous monitoring equipment will provide nearly instantaneous measurements of ambient concentrations for several pollutants. Continuous sampling involves drawing air through a commercial analyzer calibrated to produce an output that is proportional to the ambient pollutant concentration. This gives the greatest resolution but is costly, due largely to the capital and operating costs involved.

Real-time Data

Continuous or real-time monitoring involves outside (referred to as ambient) air drawn through a commercial analyzer. The resulting analyzer response produces an output that is proportional to the ambient concentration of the compound being monitored. The measurement is continuous 24 hours a day, 7 days a week and thus able to produce instantaneous or episodic data (please see health effects). Averages of the data are collected in 1-minute and 1-hour forms for detailed examination. Daily diagnostics are automated to determine operational status of all analyzers.

The Palliser Airshed continuous monitoring program allows a greater variety of monitoring than previously monitored in the past. Parameters currently measured continuously include carbon dioxide (CO), sulphur dioxide (SO2), nitrogen dioxide (NO2), ozone (O3), and total hydrocarbons (THC). Respirable particulate matter less than 2.5 microns in size (PM2.5) are also measured using continuous methods. These methods are capable of measuring concentrations well below normal detection levels, which helps in assessing potential chronic or acute exposures. Data collected for this methodology undergoes rigorous QA/QC checks which expose any deficiencies or trends with the data, creating an assessment tool to evaluate pollutant changes over time.

Meteorology measurements are also performed continuously to indicate various conditions during the collection of data. Examples of meteorological parameters include wind speed (WS), wind direction (WD), temperature (ET), relative humidity (RH), and solar/global radiation (GR). The measurements of these parameters allow the relationship of ambient air pollutants and changing weather patterns to be examined in detail.

Monthly Data

Passive systems have been developed for sulphur dioxide (SO2), ozone (O3), and nitrogen dioxide (NO2), as well as other gases, but are less precise than continuous and integrated methods. Passive sampling systems are used to collect integrated samples for analysis. Unlike the systems described above, they have no moving parts and require no electricity, making them suitable for use in remote locations. This cost effective measure allow a greater range of area to be measured, and trends can be spotted throughout the data relating to variations of seasons.

The concept requires a sampler housing reactive chemicals be exposed to ambient air for a known period. The chemicals will react to specific compounds within the atmosphere (i.e. the O3 sampler will react with O3 gases). The samplers are collected and analyzed at a laboratory to produce an average concentration for the sampling period.


NOX/NO/NO2 analyzer
NOX Analyzer

Measurement is made by a chemiluminescent based nitrogen oxides analyzer designed to measure ambient levels of NO, NO2, and NOX. The principle of measurement is based upon the reaction of the NO molecule with an internal source of ozone in an evacuated reaction cell which results in the emission of light. The analyzer is a single reaction chambered instrument that measures the NO in a sample gas which is alternately passed through or around a catalytic converter to convert the NO2 to NO. The measurement of the untreated sample provides a NO value and the measurement of the converted sample provides the NOX measurement with NO2 calculated as the difference between the two measurements.

O3 analyzer
O3 Analyzer

The O3 analyzer operates on the Ultra Violet (UV) absorption principle (Beer-Lambert relationship) of specific wavelengths of UV light created by O3. One such wavelength of light is passed through a glass sample cell that alternately contains the measurement sample and then a reference sample that is selectively scrubbed of O3. The difference in UV light attenuation between the sample and reference gas streams provides a measurement of the O3 present in the gas sample. The analyzer uses the difference based on the UV absorption principle to calculate the O3 concentration in the sample.

CO analyzer
CO Analyzer

The CO analyzer operates on the Infrared absorption principle. CO molecules absorb Infrared light in the sample mode, and in reference mode there are no CO molecules present. the signal from the two modes is subtracted and based on the air flow through the instrument, a CO concentration is derived.

PM2.5 analyzer

At the heart of the analyzer is the tapered element oscillating microbalance (TEOM), which is a patented inertial mass measurement technique for making a direct measurement of the particle mass collected on a filter in real time. Dust particles are separated via a flow splitter, and the smaller mass is collected on the filter thus changing the frequency of the oscillation. The difference in oscillation is measured and an output directly proportional to the mass is generated.

THC analyzer
THC Analyzer

The Total Hydrocarbon (THC) Analyzer offers both flexibility and reliability by combining proven Flame Ionization Detection (FID) technology with automatic diagnostics. The sample is passed through a flame, ionizing the molecule(s). Carbons released during this process are measured and an output proportional to the concentration is measured and averaged.

Meteorological Station

The Meteorological Station includes a Wind Speed Sensor and Wind Direction Sensor which provides detailed information on horizontal wind velocity and wind direction. The station also includes a temperature, relative humidity, and solar/global radiation probes that are calibrated to traceable standards.



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