NPS: Explore Nature» Air Resources Division-Special Studies:Portable Ozone Systems

Portable Ozone Monitoring Systems (POMS)

Overview

Portable ozone system at Tuweep site in Grand Canyon National Park, Arizona

A new option for ozone monitoring recently became available when a small low-power ozone analyzer was offered commercially. The National Park Service (NPS) has configured the analyzers with a datalogger, weather measurements, and solar-power on an open-frame system that is transportable and has low site impact. Two POMS versions are available: one with and one without filter-pack sampling.

Locations

US Map showing Portable Ozone Monitoring Stations

Additional Map networks» Ozone - Deposition - Meteorology - Visibility - Studies

The portable ozone systems were tested at Rocky Mountain and Isle Royale NP prior to actual deployments. Since then stations have been installed at:

Grand Canyon NP: Tuweep on the north rim
Lake Mead NRA: Meadview
Isle Royale NP
Big South Fork NRA
Black Canyon of the Gunnison NP

A table (pdf) with POMS deployments is also available as well as more detailed information in the Monitoring History Database.

The 2B Tech ozone analyzers have been used for specialized studies at:

Great Smoky Mountains NP - for ozone injury coneflower studies
Yosemite NP - spatial and vertical elevation distributions of ozone.
Joshua Tree NP - ozone gradient study.

Learn more about the individual NPS air pollutant monitoring programs.

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Procedures

Two ozone analyzers and the datalogger in weather-proof case.

The portable ozone analyzers operate on the same principle as the instruments we use in our regular network, UV absorption by ozone. To reduce the size and power, miniaturized electronics and subsystems are used in the analyzers. In the configuration used by the NPS, a primary analyzer samples ambient air all the time and a secondary analyzer is turned on briefly at night to check the first instrument. A datalogger controls the systems, collects all the data, and is used for the communications.

Data is extracted from the system using a data transfer module, by phone, or over a satellite link. Weather and CASTNet-protocol filter-pack data can also be collected. Power can be supplied with solar panels or by regular line power. Data validation, storage, and reporting follows a similar sequence as with our GPMN ozone monitoring network.

Costs estimates and equipment lists are available in a fact sheet (53 kb, PDF). Design details (175 kb, PDF) are also available for the POMS II. Operational guidelines are available in the standard operating procedure (SOP) (1 mb, PDF) and operator's guide (2.2 mb, PDF). A graph showing the results of the colocation of a portable monitor with the existing monitor at Rocky Mountain NP is also available.

The portable systems measure the following parameters:

ambient ozone
wind speed
wind direction
relative humidity
ambient temperature
rainfall
with CastNet-protocol filter pack (optional)

sulfate, nitrate, ammonium, nitric acid, sulfur dioxide

Results

View of smaller, lighter, less expensive POMS II unit ideal for ozone survey studies.

Field tests during 2002 showed that the portable systems closely matched the ozone measured at our regular monitoring stations. Lab tests of the 2B Tech ozone analyzers showed that an operational range of -10 C to 50 C gave equivalent results. Some day-to-night differences were seen in monitoring during 2004 and the portables produced early morning spikes that were offscale. This behavior was traced to a humidity sensitivity. Addition of Napion dryer tubes on the inlet of the analyzers solved both problems. Field use of the portables in 2005 and 2006 demonstrated that the humidity problem had been resolved. Co-located portable analyzers and co-located portables next to certified equivalent UV-absorption analyzers at field locations demonstrated good performance resulting in the deployment of eighteen POMS units in fifteen parks in 2006.

NPS plans to continue to use the portable ozone systems for survey and temporary monitoring projects. Plots, summaries, and hourly datasets for all the portable ozone systems are available from the interactive data query web page. Current hourly values for many of the portable systems are posted on the Current Ozone and Weather Data in National Parks webpages during the summer. POMS data can be found in the 2005 Annual Data Summary report. The report also provides a comparison between POMS data and other monitors.

Contacts

John D. Ray, Program Manager 303-969-2820

References

"Mechanism and Elementation of a Water Vapor Interference in the Measurement of Ozone by UV Absorbance," Kevin L. Wilson and John W. Birks, Environ. Sci. Technol. 40(20), pp 6361 - 6367 (2006).

"Miniaturized Ultraviolet Ozonesonde for Atmospheric Measurements," J. A. Bognar and J. W. Birks, Analytical Chemistry 68, 3059-3062 (1996)

The Model 202 ozone analyzer used in these systems is from 2B Tech: http://twobtech.com/model_202.htm