15.Jul.2026
General guideline for NO2 installations
NO₂ Sensor Coverage
In open and unobstructed parking areas, a monitoring distance of approximately 15 meters (50 feet) may be used as a preliminary guideline for NO₂ sensor placement.
As an initial design reference, each sensor may typically monitor an area of approximately 400–500 m². However, the actual effective coverage can vary significantly depending on the car park layout, ceiling height, walls, columns, ramps, supply and exhaust locations, Jet Fan airflow patterns, and vehicle traffic.
Therefore, the required number of sensors should not be determined simply by dividing the total parking area by the nominal coverage area of each sensor. Sensor placement should also consider actual airflow patterns and locations where vehicle emissions are most likely to accumulate.
Particular attention should be given to:
NO₂ Sensor Mounting Height
The mounting height of an NO₂ sensor should be determined based on the monitoring objective, vehicle exhaust characteristics, local airflow conditions, ventilation system design, and the sensor manufacturer's recommendations.
Where the primary objective is to monitor potential human exposure to NO₂, the breathing zone may be considered as part of the sensor placement strategy. A typical mounting height is approximately 1.2–1.8 meters (4–6 feet) above the finished floor.
However, NO₂ emitted from vehicle exhaust is affected by exhaust temperature, air mixing, mechanical ventilation, and Jet Fan airflow. Therefore, sensor mounting height should not be determined solely based on the density of NO₂ relative to air.
Important Considerations for Sensor Location
To obtain representative air quality measurements, NO₂ sensors should be installed in locations where surrounding air can circulate freely around the sensing element.
Where site conditions permit, installation on open interior columns may be preferable to wall mounting, as this allows the sensor to be exposed more effectively to the surrounding air.
Sensors should not be installed directly in:
Supply air streams, immediately adjacent to exhaust openings, or locations exposed to strong direct airflow from Jet Fans.
Excessive localized airflow may dilute or redirect pollutants and result in measurements that do not accurately represent the actual air quality within the monitoring zone.
NO₂ sensors also require periodic inspection and calibration. Installation locations should therefore provide sufficient accessibility for routine calibration, sensor replacement, and maintenance.
NO₂ Sensor Measurement Range
Typical NO₂ gas detection ranges for car park applications include:
0–20 ppm or 0–50 ppm
The appropriate measurement range should be selected according to the car park application, ventilation control requirements, and project specifications.
For systems primarily intended for low-concentration air quality monitoring and demand-controlled ventilation, particular attention should be given to the sensor's resolution, accuracy, and long-term stability at low concentrations, rather than selecting a sensor solely based on its maximum measurement range.
Integration of NO₂ Monitoring with Ventilation Systems
NO₂ gas detectors can be integrated with DDC, PLC, BMS, or car park ventilation control systems through standard outputs and communication interfaces such as 4–20 mA, 0–10 V, relay contacts, or RS-485 Modbus.
The ventilation system can then be controlled in stages according to the measured NO₂ concentration. For example:
Stage 1: 0.7 ppm
Activate the first stage of ventilation or increase fan speed.
Stage 2: 1.5 ppm
Increase ventilation capacity, activate additional fans, or initiate a high-level alarm condition.
The 0.7 ppm and 1.5 ppm values above are provided only as examples of a possible control strategy and should not be interpreted as mandatory regulatory alarm thresholds for all applications.
Actual setpoints should be determined in accordance with applicable local regulations, project specifications, occupational exposure requirements, and the recommendations of the equipment manufacturer.
Why Should Car Parks Consider Both CO and NO₂ Monitoring?
Traditional car park ventilation systems commonly use Carbon Monoxide (CO) as a primary indicator of vehicle exhaust pollution. However, CO and NO₂ are associated with different vehicle emission characteristics.
CO monitoring is generally more relevant to emissions from gasoline-powered vehicles, while car parks with significant traffic from diesel-powered cars, trucks, buses, or other diesel vehicles should also evaluate the need for NO₂ monitoring.
Modern car park air quality monitoring systems may therefore incorporate both:
CO (Carbon Monoxide) + NO₂ (Nitrogen Dioxide)
Using multiple gas measurements for Demand-Controlled Ventilation (DCV) allows the ventilation system to respond more effectively to actual air quality conditions than systems operating solely on fixed schedules or continuously at full ventilation capacity.
From Personnel Safety to Indoor Air Quality Management
In addition to high-concentration alarms and car park ventilation control, modern building design increasingly considers the potential health effects associated with long-term exposure to low concentrations of air pollutants.
For example, the WELL Building Standard includes more stringent NO₂ concentration targets for enhanced indoor air quality, with certain Enhanced Air Quality criteria reaching approximately 21 ppb (0.021 ppm).
This demonstrates that NO₂ monitoring is no longer limited to activating ventilation when concentrations reach alarm levels. It can also provide valuable data for indoor air quality management, smart ventilation strategies, and healthy building design.
Design Considerations
The sensor coverage, mounting heights, and alarm setpoints described in this article are provided as general engineering design guidelines only and should not be interpreted as fixed regulatory requirements applicable to every project.
Final system design should take into consideration applicable local regulations, project specifications, actual car park layout and ventilation conditions, as well as the installation and operating requirements specified by the gas detector manufacturer.
In open and unobstructed parking areas, a monitoring distance of approximately 15 meters (50 feet) may be used as a preliminary guideline for NO₂ sensor placement.
As an initial design reference, each sensor may typically monitor an area of approximately 400–500 m². However, the actual effective coverage can vary significantly depending on the car park layout, ceiling height, walls, columns, ramps, supply and exhaust locations, Jet Fan airflow patterns, and vehicle traffic.
Therefore, the required number of sensors should not be determined simply by dividing the total parking area by the nominal coverage area of each sensor. Sensor placement should also consider actual airflow patterns and locations where vehicle emissions are most likely to accumulate.
Particular attention should be given to:
- Vehicle entrances, exits, and ramps
- Areas where vehicles frequently queue or idle
- Poorly ventilated corners and potential dead zones
- Columns or other locations that provide representative air sampling
- Areas frequently occupied or accessed by diesel-powered vehicles
NO₂ Sensor Mounting Height
The mounting height of an NO₂ sensor should be determined based on the monitoring objective, vehicle exhaust characteristics, local airflow conditions, ventilation system design, and the sensor manufacturer's recommendations.
Where the primary objective is to monitor potential human exposure to NO₂, the breathing zone may be considered as part of the sensor placement strategy. A typical mounting height is approximately 1.2–1.8 meters (4–6 feet) above the finished floor.
However, NO₂ emitted from vehicle exhaust is affected by exhaust temperature, air mixing, mechanical ventilation, and Jet Fan airflow. Therefore, sensor mounting height should not be determined solely based on the density of NO₂ relative to air.
Important Considerations for Sensor Location
To obtain representative air quality measurements, NO₂ sensors should be installed in locations where surrounding air can circulate freely around the sensing element.
Where site conditions permit, installation on open interior columns may be preferable to wall mounting, as this allows the sensor to be exposed more effectively to the surrounding air.
Sensors should not be installed directly in:
Supply air streams, immediately adjacent to exhaust openings, or locations exposed to strong direct airflow from Jet Fans.
Excessive localized airflow may dilute or redirect pollutants and result in measurements that do not accurately represent the actual air quality within the monitoring zone.
NO₂ sensors also require periodic inspection and calibration. Installation locations should therefore provide sufficient accessibility for routine calibration, sensor replacement, and maintenance.
NO₂ Sensor Measurement Range
Typical NO₂ gas detection ranges for car park applications include:
0–20 ppm or 0–50 ppm
The appropriate measurement range should be selected according to the car park application, ventilation control requirements, and project specifications.
For systems primarily intended for low-concentration air quality monitoring and demand-controlled ventilation, particular attention should be given to the sensor's resolution, accuracy, and long-term stability at low concentrations, rather than selecting a sensor solely based on its maximum measurement range.
Integration of NO₂ Monitoring with Ventilation Systems
NO₂ gas detectors can be integrated with DDC, PLC, BMS, or car park ventilation control systems through standard outputs and communication interfaces such as 4–20 mA, 0–10 V, relay contacts, or RS-485 Modbus.
The ventilation system can then be controlled in stages according to the measured NO₂ concentration. For example:
Stage 1: 0.7 ppm
Activate the first stage of ventilation or increase fan speed.
Stage 2: 1.5 ppm
Increase ventilation capacity, activate additional fans, or initiate a high-level alarm condition.
The 0.7 ppm and 1.5 ppm values above are provided only as examples of a possible control strategy and should not be interpreted as mandatory regulatory alarm thresholds for all applications.
Actual setpoints should be determined in accordance with applicable local regulations, project specifications, occupational exposure requirements, and the recommendations of the equipment manufacturer.
Why Should Car Parks Consider Both CO and NO₂ Monitoring?
Traditional car park ventilation systems commonly use Carbon Monoxide (CO) as a primary indicator of vehicle exhaust pollution. However, CO and NO₂ are associated with different vehicle emission characteristics.
CO monitoring is generally more relevant to emissions from gasoline-powered vehicles, while car parks with significant traffic from diesel-powered cars, trucks, buses, or other diesel vehicles should also evaluate the need for NO₂ monitoring.
Modern car park air quality monitoring systems may therefore incorporate both:
CO (Carbon Monoxide) + NO₂ (Nitrogen Dioxide)
Using multiple gas measurements for Demand-Controlled Ventilation (DCV) allows the ventilation system to respond more effectively to actual air quality conditions than systems operating solely on fixed schedules or continuously at full ventilation capacity.
From Personnel Safety to Indoor Air Quality Management
In addition to high-concentration alarms and car park ventilation control, modern building design increasingly considers the potential health effects associated with long-term exposure to low concentrations of air pollutants.
For example, the WELL Building Standard includes more stringent NO₂ concentration targets for enhanced indoor air quality, with certain Enhanced Air Quality criteria reaching approximately 21 ppb (0.021 ppm).
This demonstrates that NO₂ monitoring is no longer limited to activating ventilation when concentrations reach alarm levels. It can also provide valuable data for indoor air quality management, smart ventilation strategies, and healthy building design.
Design Considerations
The sensor coverage, mounting heights, and alarm setpoints described in this article are provided as general engineering design guidelines only and should not be interpreted as fixed regulatory requirements applicable to every project.
Final system design should take into consideration applicable local regulations, project specifications, actual car park layout and ventilation conditions, as well as the installation and operating requirements specified by the gas detector manufacturer.
Other
-
15 Sep 2026Taiwan Industry Week 2026
-
01 Nov 20242024 Refrigeration & HVAC Taiwan
