54 August 2015
The Indoor Air Pollutant
Environment and Our
• Carbon monoxide (CO) is a colorless, odorless
gas that interferes with the delivery of oxygen
throughout the body. CO causes headaches,
dizziness, weakness, nausea, and even death.
(Ivan Blumenthal, www.ncbi.nlm.nih.gov/pmc/
❍ Sensor Chosen: MQ- 7 CO 50-3,000 PPM
Parallax gas sensor board (see Figure 1).
•Volatile organic compounds (VOCs) are chemicals
found in paints and lacquers, paint strippers,
cleaning supplies, varnishes and waxes, pesticides,
building materials and furnishings, office
equipment, moth repellents, air fresheners, and
dry-cleaned clothing. VOCs evaporate into the air
when these products are used, or sometimes even
when they are stored. (P. Wolkoff, et. al.
❍ Sensor Chosen: GROVE HCHO 1-50 PPM
Grove gas sensor board (see Figure 2).
• Combustion pollutants are gasses that come from
fuel-burning appliances. The amount depends on
the appliance, and how well it is installed,
maintained, and vented. Fuel types also vary;
typically, propane and methane. In my case, we
use propane for our kitchen stove and gas
fireplace. (A. Kazragis, A. Gailius,
❍ Sensor Chosen: MQ- 2 combustible gas and
smoke 300-10,000 PPM Grove gas sensor
board (see Figure 3).
Background and Theory
in Applying a Gas Sensor
Gas sensors are widely available for various gas
types, sensitivity levels, and different cost factors. All of
the MQ sensor series are inexpensive (MQ- 7 CO,
HOCHO, and MQ- 2 LPG) with reasonable PPM (PPM
stands for one part per million) resolution. This sensor
series uses a small inside heater in conjunction with an
electro-chemical sensor. The heater allows for good
sensitivity against a range of gasses that occur indoors
at room temperature.
The preferred sensor wiring is to connect both
sensor ‘A’ pins together and both sensor ‘B’ pins
Parallax MQ- 7
CO sensor and
GROVE MQ- 2
LPG sensor and
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