Toxic gas sensing
Air pollution sources often emit a mixture of toxic gases. For instance, diesel engines emit carbon monoxide and nitric oxides. Elevated atmospheric concentrations of these toxic gases are harmful to human health and the environment. For example, nitric oxide pollution forms acid rain.
Schematic of Electrochemical Cell
The ObservAir uses interchangeable electrochemical cells to monitor toxic gases. Cells contain three electrodes in contact with an electrolyte. Gas diffuses through a membrane and oxidizes or reduces the working electrode, thereby generating a small electrical current that is proportional to the targeted gas concentration. The reference electrode does not contact gases and generates a baseline signal. By comparing the working and reference currents, gas concentrations are logged in real time.
The ObservAir can monitor up to two of the six gaseous pollutants listed below (any combination thereof). A brief introduction is provided for each. All six are toxic to human health and the environment.
Carbon monoxide (CO): Colorless, odorless product of incomplete fossil fuel or biomass combustion.
Nitric oxide (NO): Colorless gas formed when oxygen and nitrogen react at high temperatures (>2800 F). Common sources include lightning strikes and internal combustion engines, notably diesel. Reacts with ozone to form NO2 in the atmosphere.
Nitric oxide (NO2): Reddish-brown gas formed at high temperatures, like NO. Associated with smog and acid rain. Degrades in sunlight to form ozone and NO in the atmosphere.
Hydrogen sulfide (H2S): Colorless gas released during fossil fuel extraction/processing, and formed naturally during anaerobic decay of biomass. Smells like rotten eggs.
Sulfur dioxide (SO2): Colorless, pungent gas that is mainly emitted by fossil fuel combustion (notably coal power plants), but also by volcanic eruptions and chemical processing.
Ozone (O3): Light blue gas with distinctive smell. Ground-level ozone is a secondary pollutant, formed when NO2 and other gases chemically react in the atmosphere.