Sensor Network Testbed Proposed
California government officials are challenged annually to reduce ground-level ozone. While air quality in terms of ozone in southern California has ranked second worst in the nation for the past two years, the area suffered no Stage 1 alerts in the year 2000.¹ (Federal ozone standards classify a Stage 1 episode as a 1-hour period in which ozone levels exceed 0.20 ppm.) In addition, southern California finished the year with only 17 health advisories, a standard that indicates greater than 0.15 ppm ozone in one hour. These trends indicate great improvement in air quality for the state over past decades, underscoring the value and need to continue careful monitoring of ozone levels.
People often find confusing the fact that ground-level ozone (the main component of smog) differs from the ozone that exists above the troposphere. While high ozone forms a protective shield that filters out UV radiation from the sun that can damage human proteins and DNA, ground-level ozone can irritate eyes, destroy lung tissue, and exacerbate chronic respiratory diseases.² Ozone is detrimental not only to humans but also to plants, as is often evidenced by unhealthy trees that flank busy roads and freeways.
In this context, Calit² PIs seek to build a small wireless sensor network to monitor not only air but also water pollution. The network will provide an experimentation platform to develop technologies and methodologies for data acquisition and analysis. We expect to acquire off-the-shelf sensors and package them in a single wireless "station." We expect to deploy these stations at eight locations around UCSD and five in the Santa Margarita ecological preserve (managed by SDSU) in northeast San Diego County. All stations will be equipped with video monitoring equipment, and statistical information will be channeled to and made publicly available on the Internet.
Air Pollution
Initial sensing stations for air contaminants will detect temperature, relative humidity, and carbon monoxide (CO), with subsequent models being equipped with additional sensors for nitrogen oxides (NOx), ozone, and carbon dioxide (CO2). CO is a colorless, tasteless, and odorless gas produced as a by-product of combustion. When absorbed by the body, it is attracted to hemoglobin in the bloodstream and, upon binding, prevents the hemoglobin from transporting oxygen from the lungs to cells, tissues, and vital organs. While exposure to CO over long periods of time is dangerous, the long half-life of the carboxyhemoglobin formed in the blood (about five hours) can extend and compound the effects of even very short-term exposure. In the U.S. alone, some 10,000 people seek medical attention, and nearly 5,000 die, from CO poisoning each year.³
Over time we want to upgrade the sensor arrays to detect additional gases (NOx, ozone, and CO2). The oxides NO and NO2 can react with volatile organic compounds (which are also by-products of automobile emissions) to create ground-level ozone and are responsible for the production of acid rain. Automobiles, trucks, and buses generate about half of these harmful compounds, with the remaining half released by industries and power plants. NOx is monitored over vast areas of the lower atmosphere via an existing satellite network, but our network of compact, localized detectors would qualify and expand upon this database.
Although CO2 is a natural component of the air, excess levels of the gas induced by burning fossil fuels can be harmful environmentally. High concentrations of CO2 in the atmosphere trap the sun's heat and contribute to global warming. Presently, there are no federally established standards for CO2, as the gas poses no direct human health risks.
We expect to implement the air sensing stations at a parking garage, a bus stop, a bridge, and a loading dock, all at UCSD. For comparative analysis (away from environments heavily populated by cars and busses), we will install stations inside and outside Pacific Hall, one of the chemistry and biology research buildings on campus.
Water Pollutants
Our initial devices will not detect specific water pollutants but monitor changes in the temperature and pH of the water to obtain a general indication of water quality. For example, dissolved organic compounds and other chemical contaminants can alter pH levels, pinpointing areas of high toxicity. Sensing stations will be sited off the Scripps Pier and in local drainage systems.
Task List
Our task list includes the following:
- Construction of prototype air quality monitor
- Construction of prototype water quality monitor
- Development of protocols for testing and calibration of sensor modules
- Validation and testing of stations
- Fabrication and laboratory reproducibility testing of sensor arrays
- Distribution of stations to specified locations
- Wiring, programming, and evaluation of Internet compatibility
Participants
Expected participants include the following:
Tom Garcia (Graviton)
James S. Ha (Quantum Group)
Andy Kummel (UCSD Department of Chemistry and Biochemistry)
Michael Nova (Graviton)
Michael Sailor (UCSD Department of Chemistry and Biochemistry)
Ivan Schuller (UCSD Physics)
Jan Talbot (UCSD MAE)
Frank Vernon (UCSD SIO)
Thanks to Jamie Link, a Calit² graduate fellow, and Tina Perez, a UCSD undergraduate student, who assisted in preparing this document.
References
1. http://www.aqmd.gov/news1/Smog_season_2000.htm
2. wysiwyg://17/http://www.dep.state.pa.us
3. http://www.coma-cosha.org/detectors.htm
4. http://home.ica.net/~jwilmot/fire/carbonmonoxide.htm
5. http://www.mcagcc.usmc.mil/Base/firedept/prevention/co2.htm