Benzene Sensor


Benzene (C6H6) is an anthropogenic chemical associated with a range of acute and long-term adverse health effects and diseases, including cancer and aplastic anemia. Exposure to benzene can occur occupationally and domestically, as a consequence of using petroleum products, active/passive smoking, industrial leakage, and forest fires. The Environmental Protection Agency (EPA) defines the maximum contaminant level (MCL) for benzene in an aqueous environment to be 5ppb; the short-term exposure limit for 15 minutes is 5ppm and the maximum exposure standard for 8 hours is 1ppm.

Because of its strong effects on human health, sensors are needed to detect trace quantities of benzene yet no such product exists in the market, particularly one with suitable detection limit, reasonable detection bandwidth, and portability. I work with Dr. Ritobrata Sur under supervision of Prof. Ronald K. Hanson and Prof. Robert B. Jackson for a GPS-enabled benzene-specific sensor that is both in-situ and field-deployable.

Challenges

  • Size/Portability

  • Cost

  • Bandwidth

  • Sticky molecule

  • Broadband absorption

  • Interference

  • Easy-to-use

  • Flexibility

Approaches

  • Multi-pass design and packaging

  • Design tradeoff, no bottleneck or waste

  • Laser absorption spectroscopy

  • Flowing cell scheme

  • Wavelength modulation

  • Lower-pressure features

  • Backend code for processing/analysis

  • Battery-powered & cordless

Laboratory calibration and testing

The results suggest a detection limit of 0.2ppm at 2Hz bandwidth. The oscillations are partially attributable to inadequacy of the mass flow controllers; better detection limits can be achieved with longer averaging time or higher optical path length.

Field campaign

Sensor independently runs in the truck of my car, with inlet hose installed upstream, on the front passenger side of the car.

f.t. Prof. Rob Jackson & Colin Finnegan

Results: observed occurrences of elevated benzene (1ppm) concentration in heavy traffic

Emission likely comes from unburnt gasoline in car exhaust.

Results: elevated atmospheric benzene levels of 2-20ppm near gas station nozzles

Gasoline contains benzene and amounts depend on providers.