The Leading Edge of Las Vegas. Dr. Vic Etyemezian, A DRI air quality scientist in Las Vegas, installs a small Doppler SODAR on the roof of Palo Verde High School on the western edge of the city. The instrument tracks the movement of air carrying pollutants into the valley from southern California.

Federal enforcers, armed with strengthening data showing the correlation between serious respiratory ailments and extremely small airborne particles and other air pollutants, are focusing on the bottom line of public health.

Under the National Ambient Air Quality Standards (NAAQS), strict limits have been imposed on the levels of extremely small airborne particulates, ozone, and carbon monoxide, and more significant, a new approach for assessing the long-term impact of local planning on air quality, a concept called "transportation conformity," is forcing local air quality planners to completely rethink their once acceptable strategies.

This new approach doesn't mean we're all supposed to start driving identical low-emission vehicles. Transportation conformity borrows the non-degradation approach to air quality that's been used to protect public parks and recreation areas, and applies it to any transportation project involving the expenditure of federal funds. It's a sort of "zero tolerance" for exacerbating pollution if federal funds are involved.

The fastest growing metropolitan area in the country, Las Vegas is one of six urban areas considered by the U.S. Environmental Protection Agency to be in "serious" violation of the NAAQS for airborne particulates. Air quality authorities, caught in a squeeze between rapid growth and tightening federal regulations, are fighting day-to-day at the street level with auto smog checks, better traffic controls, construction site dust inspections and special phone lines for citizen to report violations.

At the strategic level, the Clark County's comprehensive planners are are trying to anticipate air quality impacts on a scale of decades, working in a setting where a year's growth for them equals a decade or more for most major cities.

Their visions of new traffic corridors, monorails, and expanded mass transit run head on into the implications of transportation conformity in arguments with federal regulators, i.e., does new freeway capacity merely encourage more outlying construction, more driving, and further auto pollution, or does it help reduce the clouds of emissions that build over stalled traffic?

What's Blowing in the Wind. Dr. Bob Keislar of DRI puts a protective cover over the speaker/receiver array on a large Doppler SODAR located in Jean, Nevada. The high frequency sound pulses from the SODAR reflect off moving air at various elevations and reveal the direction and speed of winds that may transport pollution into southern Nevada.

And it's not just federal agencies that have southern Nevada authorities looking over their shoulders. The local population, in a clear and constant voice, has plainly stated that air quality is at the top of their list of local government concerns.

Joining in the battle with Clark County and federal agencies, DRI scientists are now working at both the short- and long-term ends of the clean air spectrum in a new $1 million, three-year research effort funded by the National Transportation Administration.

Known as the Southern Nevada Air Quality Study (SNAQS), the project's goals are to develop new, high tech weapons against local dust and vehicle pollutant sources, to determine how much of the particulate load is locally produced and how much is imported, and to design advanced air quality modeling tools with applicability for urban health efforts well beyond the southern Nevada desert.

Dr. John Watson, DRI's principal investigator for the new research program, says new pollutant sensing technology, combined with geographic information systems (GIS) capabilities and regional airshed information, will combine to help local planners understand and manage the complex character of air pollution conditions better.

"A computer-based model is only valuable to the extent that the information upon which it is based accurately represents the condition being modeled," Watson says. In the past, the state-of-the-art in modeling urban air pollution has been heavily based on statistical analyses, definitely useful for defining current problems, but not sufficient for evaluating the effectiveness of different possible approaches for solving those problems.

According to Watson, "SNAQS is an experimental effort to develop the basis of a new model that can be used predictively while producing some practical new technology and methodology to support it."

Additional DRI research faculty working with Watson on the project are Drs. Judy Chow, Vic Etyemezian, Mark Green, Robert Keislar, Darko Koracin, Hampden Kuhns, Hans Moosmüller, and William Stockwell, all of DRI's Division of Atmospheric Sciences, and David Schorran of DRI's Division of Earth and Ecosystems Sciences. Dr. Brian Johnson, and associate professor of chemistry at the University of Nevada, Las Vegas, is also working on the project.

To get a handle on road dust, DRI will equip project vehicles with particulate monitors that will measure the concentration of particles in the air in front of and behind the vehicle's front tire, giving an indication of the amount of road dust emissions contributed from streets in various locations. Coupled with a global positioning system that pinpoints the measurements within meters, the method creates a map showing sources of pollutants are entering the valley's airshed from the streets and roadways.

"It's not hard to spot a plume of visible dust and say, 'Hey, we've got to control that'," Watson says. "However, our past studies on dust loading here have indicated that a lot of the fine particles are lofted by wind and traffic from streets over more widely dispersed areas, and those particles can't be seen by a casual observer."

Not too far from an obvious dust source, Watson says, the levels drop back toward urban concentrations, but the valley's overall readings are staying pretty high.

"This information can allow the county to zero in on problem areas for street cleaning and other actions and perhaps allocate some extra effort on what may be the specific off-road sources of a neighborhood's road dust problem, a construction site or an unpaved road or parking lot." As in most metropolitan areas, automobile and diesel emissions are the cause of most of the air pollution. For decades, universal smog checks have been one of the primary tactics used at the local level to reduce these emissions: every car, every year, whether they need it or not. In recent years, local air quality managers have been experimenting with a new approach based on identifying the roughly 20 percent of the vehicles on the road that are responsible for as much as half of the emissions. One of DRI's tasks under the SNAQS project is to develop a new instrument that will help make this approach more effective.

LIDAR Than Air: Prototype Vehicle Emissions Detector. Dr. Hans Moosmuller, right, adjusts the heat sink holding an infrared laser of a prototype LIDAR while Dr. Bob Keisler attaches the telescope that will direct the laser's beam through vehicle tail pipe plumes to detect particulate emissions. The LIDAR sits on an instrument that will also analyze carbon monoxide, hydrocarbons, carbon dioxide, and oxides of nitrogen emitted from tail pipes as vehicles pass by selected monitoring locations in the Las Vegas valley.

Using an infrared laser known as a LIDAR, field operators stationed at selected locations around the valley can measure the particulates coming from individual exhaust pipes or lofted off the road as the vehicles pass through the beam. By comparing the measurements just before the vehicle passes with those taken immediately after, the contributions of particulates from that vehicle can be determined.

The LIDAR is operated in conjunction with a commercially available instrument that uses a standard infrared beam to measure the carbon monoxide, hydrocarbons, and carbon dioxide, and with an ultraviolet beam to measure the oxides of nitrogen emitted from tailpipes. All together, they produce a pretty complete picture of the on-road performance of individual vehicles.

After the LIDAR is calibrated on a carefully controlled section of roadway, it will be employed at various locations around the valley, most likely at freeway on-ramps and other locations where engines are put under a heavier than normal load.

Working with a database from the Nevada Department of Motor Vehicles, the exhaust levels of passing autos can be compared to the last smog test data and other information to indicate the effectiveness of the smog tests. This information can be used to suggest possible ways to improve emission performance.

Don't Blame the Desert for the Dust. Left undisturbed, desert surfaces will contribute only modestly to particulate levels as wind speeds increase, compared to dramatic increases in urban areas with construction activitiy as well as unpaved roads and parking areas. This graph is based on data from previous studies in sourthern Nevada measuring PM10 particulates - only one-fifth the diamaeter of a human hair or smaller - which can be inhaled and affect human health.

These improvements may range from repairs and simple tune-ups to correcting illegally modified exhaust systems. To test this approach, DRI has participated in field experiments where high-emitting vehicles were identified on the road and repaired at the project's expense while the vehicles' owners used a free rental vehicle for a day or two.

"The interesting thing we found in many of these on-road traffic studies was that it isn't just old junkers that are the high emitters," Watson points out. "Later model vehicles can produce a lot of smog if they're out of tune, have mechanical problems, or the owners have made modification that defeat the smog control system, intentionally or otherwise."

From there, in addition to targeting high emitters, further control strategies such as public education to minimize cold starts or re-engineering on-ramps with gentler slopes can be identified. Incorporated with the county's geographic information system (GIS) and an extensive travel-load model showing traffic volumes by time of day and location, the new data can produce a dynamic emissions model describing the variable character of air quality conditions across the valley. The GIS emissions model can help identify where the major sources of vehicle pollution are located. In addition, the model can be used for planning purposes to determine the effectiveness of emissions controls such as paving dirt roads, development of a light rail system, designation of car pool lanes on expressways and major thoroughfares, and the expansion of existing bus routes.

The Dirt on Dust Dr. Hampden Kuhns, a DRI air quality scientist in Las Vegas, shows the sensor positioned behind the front tire of a vehicle to measure extemely small, invisible particles of dust and other pollutants kicked up by traffic along various roadways around Las Vegas. The sensor on the hood measures particulate levels in the air just before the vehicle stirs them up.

The SNAQS project isn't only looking at the "home grown" additives to the valley's air, because not all of the air pollutants found in Las Vegas are produced there.

In August, DRI scientists established an instrumented site at Jean, Nevada, and began sampling the air moving into the valley from southern California. Doppler SODAR devices that reflect high frequency sound pulses off air moving at various altitudes determine the direction and speed of the winds. Other instruments at that site measure ozone, methyl chloroform and the very small particles that can remain in suspension for long periods and can be transported long distances. The methyl chloroform, found in very small amounts, is specific to industrial emissions in the Los Angeles Basin and acts as a tracer to show the origination of the pollutant plume.

Watson notes that previous analyses have shown that air pollutant transport into Las Vegas from the southwest is most common during the summer, when ozone readings are higher in Las Vegas. Winter airflow, when particulate levels are more of an issue in Las Vegas Valley, is more variable, and the local contributions and imported levels need to be distinguished.

According to Watson, "NAAQS imposes a hard ceiling on how high the levels of smaller particulates can go, so the only room southern Nevada air quality managers have to maneuver in is the difference between what's being transported into the area and that ceiling."

"This leads into an even bigger aspect of the transportation conformity concept. Las Vegas is one of the major metropolitan sources of particulates in the Southwest, along with Los Angeles, Phoenix, and Tucson. At some point, all of these cities are going to be called on to reconcile the impacts these particulates have on visibility and on exposed downwind populations," Watson says. "The federal government hasn't brought that issue up yet, but it's definitely on the short list." Vehicle exhaust, dust particles and outside pollutant sources-all big obstacles for southern Nevada planners and air quality managers eyeing the big federal stick. With the foundation for a transportation emissions model developed by DRI in place, they should have a better chance in staying closer to the carrot.

~ John Doherty

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