Where I Stand: Despite improvements, air quality still a concern

Friday, Aug. 9, 1996 | 11:59 a.m.

TIRED OF DAYS when you can't see the mountains? Today's guest columnist, Michael Naylor, director of the Air Pollution Control Division of the Clark County Health District, discusses how environmental controls have improved the air in the Las Vegas Valley, even though it doesn't look like it.

IS AIR QUALITY in the Las Vegas Valley improving or deteriorating?

The government -- at the federal, state and local levels -- has been working for decades to improve air quality. For most indicators of air pollution, their efforts have been successful, despite our rapid growth in population.

Although progress has been made in reducing or controlling carbon monoxide, inhalable particulate matter and other EPA-regulated pollutants, there has been a decline in visual air quality.

The Clark County Health District monitors for inhalable particulate matter, ozone, carbon monoxide, nitrogen dioxide, sulfur dioxide, a visibility index, pollen, spores and odor. These pollutants are present as gases or solids. Several air pollutants, such as ozone and carbon monoxide, cannot be seen or smelled.

One of the most conspicuous forms of our pollution is the clouds of blowing dust during high winds. The smaller particles of dust consist of very tiny fragments of soil particles, smaller than 10 millionths of a meter (10 micrometers) or half of one-thousandth of an inch. These can be inhaled into our lungs and are identified as inhalable particulate.

Standards for air quality are based on EPA-sponsored health effects research. As long as air pollution levels are within these public health standards, the EPA indicates that public health is protected. When standards for a pollutant are exceeded, the EPA classifies the surrounding area as "non-attainment."

There are only two pollutants for which the EPA classifies the Las Vegas area as non-attainment: carbon monoxide and dust. The valley is in attainment of the EPA standards for ozone, nitrogen dioxide and sulfur dioxide.

Based on more than 10 years of monitoring, the district has seen carbon monoxide levels drop substantially, while inhalable particulate matter levels have dropped only slightly.

The carbon monoxide levels in the Las Vegas Valley have been dropping for two decades, despite a tripling of daily vehicle miles. This is the result of cleaner, newer cars, Nevada smog check requirements, the district's oxygenated gasoline program and the Division of Agriculture's wintertime program limiting Reid vapor pressure in gasoline. Improvements in roads/highways and traffic light signals have helped. The combination of federal, state and local carbon monoxide control measures has proved to be relatively inexpensive and effective.

Since 1988, the only carbon monoxide monitor in the valley (out of 12 sites) to measure excess levels has been the well-publicized East Charleston/28th Street station, which experiences relatively low winds during wintertime inversion episodes. We suspect the levels measured there are also distorted by the emissions from cars starting up in an adjacent parking lot that disperse slowly because of nearby trees and block walls.

With the EPA's endorsement, two new monitors in the same area -- at Crestwood and Sunrise Acres -- became operational in July. They should improve the representation of carbon monoxide levels in the area.

Further reduction in emissions of carbon monoxide will depend on whether smog check stations and roadside monitoring can improve the ability to identify and repair the minority of vehicles that account for most of the overall emissions. This will be a challenge, since the cost of effective repair may far exceed the maximum amounts that vehicle owners must pay: $100 to $200.

The modest improvement in inhalable particulate matter levels is attributable to better compliance by contractors at construction sites and by operators at sand and gravel processing facilities. Recently, larger penalties have been imposed by the APC Hearing Board.

With the participation of several public works departments, the district is expediting a program to pave busy unpaved roads. Several miles are being paved this year under the program.

We can expect dust levels to improve, but it is unlikely that there can be compliance with the standard on all occasions. On some windy days, neighborhood air quality stations will record unhealthful levels of inhalable particulate matter if there are significant nearby sources of particulate, such as disturbed vacant land, ongoing construction activity and busy unpaved roads. We also experience some regional episodes when nearly all stations measure excessive levels.

Despite the progress noted above, visual air quality appears to be declining.

The visibility index for urban haze is measured in units of visual range. During the summer, at the central valley station, the morning visual range drops to as low as 10 to 15 miles. The afternoon visual range is typically 60 to 100 miles. The station has been showing an increased number of days per season with poor visibility and a decrease in the number of days with good visibility.

Some examples: In the fourth quarter of 1994, there were eight days when the visual range at 8 a.m. was less than 10 miles; during the fourth quarter of 1995, there were 10 such days. During the first two quarters of 1995, there were 79 days with noon-time visibility exceeding 50 miles. In 1996, this dropped to 69 days during the same period.

Visibility impairment relates especially to the smallest particles in the inhalable size range. They are only one-millionth of a meter (one micrometer) in width, or less than one ten-thousandth of an inch.

Visual air quality is not measured with an ambient air quality standard. Many people are perplexed when, despite low levels of inhalable particulate matter, carbon monoxide and ozone, the day appears to be hazy. The Clark County Department of Comprehensive Planning and the health district are seeking to evaluate causes of the poor visual air quality and strategies for improvement. Limited research to date suggests the tiny soil particles are mostly responsible.