Understanding the spatial and temporal distribution of carbon monoxide (CO)
is key to being able to establish appropriate control strategies. Studies
of CO in urban areas have traditionally used either multiple reference
type instrumented sites or "saturated" areas with bag samplers. The saturation
type studies are a brute force method of collecting air samples to better
understand the spatial distribution of CO. By their nature the studies
have required labor intensive methods to deploy and retrieve samples and
perform the analysis. While the bag type samplers worked for longer averages,
they have lacked the time resolution desired to really understand the behavior
of urban CO plumes.
During the winter of 2001/2002, I, along with T&B Systems, designed
a CO saturation study using a new and inexpensive technology for a saturation
study in the Las Vegas Valley which is a region that has traditionally
experienced CO levels in excess of the national ambient air quality standard.
In recent years the CO levels have dropped in the valley as a result of
extensive control measures and traffic control improvements in spite of
this being one of the fastest growing urban areas in the nation. A question
that was raised was whether the observed drop in concentrations was due to
actually improved air quality, or whether it was a case of not measuring
for CO in the correct regions. The study was designed to answer this question
using two technologies. One technology was the saturation of the valley with
CO measurement sites. The second technology was mobile sampling using an
instrumented van to map out the CO distribution during meteorological and
emissions conditions conducive to higher CO levels.
The overall study was funded by Clark County and consisted of three
phases:
As a key ingredient for the study, the mobile van was designed to map
in real-time the observed CO concentrations and aid in the selection of fixed
sites for further deployment of the saturation network samplers. The van
was outfitted with a reference type CO analyzer as well as two CO type data
loggers, similar to those used for the fixed site data collection. To further
aid in understanding the role of meteorological conditions, outside ambient
temperature was also measured. A GPS system was used to document the van
position as well as provide a real-time display of position on a street map
of Las Vegas. A digital camera documented the traffic in front of the van
by taking time-stamped pictures every 30 seconds. All position and CO data
were recorded as one-minute averages. Three laptop computers, operating through
a local area network, continuously logged and updated navigational and
data displays on two of the computers so that real-time observations and
decisions could be made. 