• CARBON MONOXIDE
  
• OZONE
  
• NITROGEN DIOXIDE
  
• SULFUR DIOXIDE
  
• PARTICULATE MATTER AS PM10
  
• PARTICULATE MATTER AS PM2.5
  
  

CARBON MONOXIDE

The Nevada and national standard for a one-hour period is 35 ppm carbon monoxide. The eight-hour average must not reach 9.5 ppm under the national standard of 9 ppm. At altitudes above 5,000 feet, the state eight-hour standard is reduced to 6.0 ppm, because of the decrease in available oxygen at higher altitudes. The lower level of 6.0 ppm for eight hours provides better protection of human health and welfare at high elevations. The Nevada monitoring sites at Lake Tahoe are the only monitoring sites in the state currently subject to this elevation-related state standard. Following are summaries of the findings for carbon monoxide monitoring in Nevada.

In Carson City, the East Fifth Street site recorded lower carbon monoxide concentrations than other Carson City sites as a result of this site's greater distance from major traffic corridors. The Roberts House and Ann Street sites in the downtown area are similar with respect to proximity to heavy upwind traffic along North Carson Street (US 395) and residential wood burning. No exceedances were recorded and there was no substantial change in concentrations over the years monitored that cannot be attributed to meteorological conditions. The Long Street site, a few blocks northeast of the Roberts House site, recorded concentrations lower than the concentrations previously recorded at the Roberts House site.

At Stateline, carbon monoxide concentrations monitored along the edge of the Horizon Casino Resort parking lot, downwind from the casino core area, were low, based on available data for the last two decades. Nonetheless, the Lake Tahoe hydrographic basin was designated a nonattainment area (severity of nonattainment not classified) for carbon monoxide by the EPA based on monitoring at South Lake Tahoe, California and on monitoring at Stateline in the 1970's. On June 1, 1998 the California side of the Lake Tahoe hydrographic basin was redesignated to attainment of the carbon monoxide standards. The State of Nevada requested redesignation of the Nevada side of the Lake Tahoe hydrographic basin to attainment of the carbon monoxide standards and submitted a limited maintenance plan to the EPA. As part of this plan and by multiagency cooperative agreement, the California Air Resources Board is conducting carbon monoxide monitoring at Harvey's Resort Hotel, very close to the thoroughfare through the casino complex at Stateline. This is a microscale site, which monitors the highest concentrations. There have been no violations of the standard at this site since monitoring began in October 1999.

Monitoring in Minden for 1998 and 1999 showed low carbon monoxide concentrations.

OZONE

The national one-hour ozone standard of 0.12 ppm is attained when, based on a three-year average, the expected number of days per year with a maximum hourly average above the standard is not more than one. The 1997 national eight-hour standard is based on a three-year average of the annual fourth-highest daily maximum eight-hour average ozone concentrations. This three-year average is not to exceed 0.08 ppm. The state ozone standard, a one-hour average concentration not to be exceeded, is 0.12 ppm. The exception is the Lake Tahoe Basin where the state standard is 0.10 ppm.

There were no violations of the national one-hour or eight-hour standard within the State's jurisdiction. The State submitted its eight-hour ozone designation requests to the EPA, and on April 15, 2004 the EPA designated all the State's jurisdiction as attainment/ unclassifiable for the new eight-hour ozone standard.

Clark County has areas being designated as nonattainment for the new eight-hour ozone standard.

NITROGEN DIOXIDE

The standard for nitrogen oxide compounds is related to the levels of nitrogen dioxide (NO2). The state standard for nitrogen dioxide in effect until late 2002, expressed as the annual arithmetic mean (yearly average), is 0.05 ppm. The national nitrogen dioxide annual standard is 0.053 ppm.

There are no areas in Nevada designated nonattainment for nitrogen dioxide. SLAMS monitoring for nitrogen dioxide has been performed in Stateline, and Carson City. Nitrogen dioxide concentrations are generally less than one-fifth of the standard.

SULFUR DIOXIDE

Because sulfur dioxide can have long-term as well as short-term effects, three separate standards have been established. The first health-related, or primary, standard is the annual arithmetic mean (yearly average). A yearly safe exposure level of 0.030 ppm has been established for the public. The other health-related standard, a 24-hour (daily) average, is 0.14 ppm. The national secondary standard and state standard require that an exposure for a three-hour period not exceed an average of 0.5 ppm.

The state and local agencies did not operate sulfur dioxide monitoring sites for most of the report period. Monitoring data from industrial sources indicate that the sulfur dioxide standard was not violated during the period under review.

The central Steptoe Valley in the Ely area was listed by the EPA until 2002 as not meeting primary standards for SO2. This designation was based on copper smelting activity at McGill that ceased operation in 1983. The Nevada Bureau of Air Quality Planning initiated a request by the State of Nevada for the EPA to reclassify this area to attainment. The reclassification became effective on April 12, 2002.

PARTICULATE MATTER AS PM10

Total suspended particulates (TSP) monitoring was abandoned in favor of PM10 monitoring by the EPA in 1987 and by the state in 1991. The PM10 standards reflect the important health effects of particles in the inhalable size range, while eliminating from consideration the larger suspended particles previously sampled under the TSP standards. The PM10 annual standard is 50 µg/m3. The 24-hour PM10 standard is 150 µg/m3. As discussed in the section on state and national ambient air quality standards, the national 24-hour PM10 standard is based on the number of expected exceedances from the analysis of three or more years' data. The 1997 PM10 standards, which involve calculating concentrations for local conditions instead of standard conditions, and which use 99th percentile concentrations instead of the number of exceedances for comparison to the 24-hour standard, were vacated by the courts (D.C. Circuit, May 14, 1999). Only the original PM10 standard is in effect.

The number of exceedances of the 24-hour standard can be affected by the sampling schedule, when samples are not collected on an every-day schedule. For example, the number of exceedances monitored may need to be multiplied by six when sampling is on an every-sixth-day schedule, or be multiplied by three when sampling is on an every-third-day schedule. An every-sixth-day schedule can be identified when the number of samples for a complete calendar year approaches 61; an every-third-day schedule can be identified when the number of samples for a complete calendar year approaches 122. Following are summaries of the findings for PM10 monitoring in Nevada:

With the exception of monitoring at Pahrump, PM10 concentrations were below the annual and 24-hour standards at all state operated monitoring sites for the purpose of regulatory determinations. Although exceedances of the 24-hour standard were recorded, they were discounted from nonattainment determinations under the EPA policies for exceptional events and natural events. An exceedance of the 24-hour standard was recorded in Carson City on January 10, 1997, the EPA classified the exceedance an exceptional event related to silt deposition from a flood. In Battle Mountain during 1990, one exceedance of the 24-hour standard was excluded from regulatory determinations as an exceptional event due to high winds. Exceedances of the 24-hour standard on August 13, 1996 in McGill and on October 18, 1996, April 23, 1998 and January 11, 2000 in Battle Mountain were excluded as natural events due to high winds. An exceedance of the 24-hour standard in Battle Mountain on August 2, 2000 was flagged by the Bureau of Air Quality Planning as a natural event for wildfire smoke and discounted. PM10 data from one site in Lovelock, the high school, were disqualified by the EPA due to siting concerns. There were no other exceedances of the 24-hour or annual standards for the years reported at these locations.

Monitoring at Pahrump has resulted in multiple exceedances of the 24-hour PM10 standard since 2001. The exceedances were not all related to high winds. Exceedances at Pahrump related to high winds can no longer be discounted for regulatory purposes under the EPA PM10 natural events policy, since the exceedances also relate to man-made surface disturbances where the best available measures to control fugitive dust have not been applied. As a result of these exceedances a portion of the Pahrump Valley, in Nye County, is in nonattainment for particulate matter less than 10 microns (PM10). The EPA, State, Pahrump Town Board and Nye County have agreed to use a memorandum of understanding (MOU) to address the nonattainment classification. The MOU was signed in September 2003, giving the cooperative agencies until 2009 to bring the area back into attainment. Control strategies must be in place by 2006 and must remain in place to ensure that the Pahrump Valley will continue to attain the standards in the future.

PARTICULATE MATTER AS PM2.5

The annual PM2.5 standard is met when the three-year spatial average of the annual averages of the monitors in an area does not exceed 15.0 µg/m3. The 24-hour PM2.5 standard is met when the three-year average of the annual 98th percentile of the distribution of concentrations at each monitoring site does not exceed 65 µg/m3. As discussed under the heading, Particulate Matter as PM10, the number of exceedances can be affected by the sampling schedule when every-day sampling is not done.

Monitoring for PM2.5 was not required by the EPA within the jurisdiction of the state. Screening monitoring was conducted at three locations in the jurisdiction of the state beginning in 1998 and 1999 with uncertified monitors, which are not as labor-intensive as FRM monitors. The screening monitoring indicated that PM2.5 concentrations were generally low at all three locations: Carson City, Gardnerville, and Fernley. The highest concentrations of the year at these locations can be expected when winds are relatively calm during the evening, night and early morning hours of the months of December and January. This is indicative of residential wood smoke as the source of the higher concentrations. In addition, an exceedance (100 mg/m3) of the 24-hour PM2.5 standard was recorded at Incline Village in 2001 by Washoe County as a result of a smoke plume impact from a California forest fire in the El Dorado National Forest, again indicating smoke as the source of highest PM2.5 concentrations for rural Nevada.

Attainment classifications based on three years of data collected with EPA-certified federal reference method (FRM) monitors were published by the EPA in December 2004. The EPA has designated all air quality jurisdictions in Nevada as attainment/unclassifiable for the PM2.5 standard.