Supplemental Information for

The Nevada Rural Ozone Initiative (NVROI): Insights to Understanding Air Pollution in Complex Terrain

Mae Sexauer Gustin1, Rebekka Fine1, Matthieu Miller1, Dan Jaffe2, Joel Burley3

1Department of Natural Resources and Environmental Science, MS 186, University of Nevada-Reno, Reno, NV, USA 895572School of Science and Technology, University of Washington-Bothell, 18115 Campus Way NE, Bothell,3Department of Chemistry, Saint Mary's College of California, Moraga, CA 94575-4527, USA

Corresponding Author: Mae Sexauer Gustin, 001-775-784-4203, mgustin@cabnr.unr.edu

Detailed description of potential sources of ozone to Nevada

Ozone in the marine boundary layer is generally considered to be low given the high number of

reactants (cf. Donaldson and George, 2012; Jammoul et al., 2008; Kramm et al., 1995); however, past

measurements of O3 off the coast of southern California indicate that pollution derived from urban areas in

California may accumulate offshore (cf. Rosenthal et al., 2003).

Emissions from other states, in particular California, are important to consider because Nevada is

generally downwind. For example, based on data collected in 2001, Lin (2010) showed an addition of 1000 tons

of NOx to California and Nevada emissions would affect the 90th percentile O3 in Nevada. Based on the 2008

National Emission Inventory (NEI), NOx emissions in Nevada were roughly 104 tons per year. Of these NOx

emissions, 42% were from highway vehicles, 29% off highway vehicles, 18% fossil fuel production, and 11% were

biogenic emissions. Biogenic NOx emissions in Nevada have not been directly measured; however, they are

expected to be low due to low concentrations of nitrogen in the soils (Personal Communication: Professor Dale

Johnson, Soil Scientist, Emeritus Faculty University of Nevada-Reno), lack of moisture, and sparse vegetation. An

additional nitrogen source that is not accounted for in the NEI is emission from heap leaching at mines, in

particular emissions of HCN, NO3-, NO2

- , and NH4+, which would potentially be released from cyanide solution (cf.

Johnson et al., 2000). However, this source is likely to be low given the fact that the mining industry wants to

minimize loss of cyanide solution. In contrast to NOx emissions in Nevada, the mean annual NOx emissions for

California in 2008 were ~106 tons y-1 with 78% being derived from mobile sources

(http://www.epa.gov/ttnchie1/net/2008inventory.html).

Stratospheric intrusions have been suggested to contribute up to 40 ppbv to the surface in the Western

USA (cf. Langford et al., 2009; Langford et al., 2012; Langford and Reid, 1998; Lin et al., 2012). There is current

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debate about the relative importance of this process (see discussion in Lin et al. 2012), and the frequency has

been suggested to vary from year to year (cf. Bourqui and Trepanier, 2010; Lin et al. 2012).

Additional sources include lightning and wildfires. It is estimated that Nevada is hit with 1000 strikes/day

during May to September (http://www.wrcc.dri.edu/fire/tidbits.html). Wildfires are typically designated as a

natural source; however, these may also be due to anthropogenic actions or forcings associated with climate

change. The extent to which wildfire emissions contribute O3 and precursors will depend on fire characteristics

(Jaffe and Wigder, 2012) and distance from the fire.

Detailed description of development of the NVROI network

Summary data from the Western Regional Climate Center (WRCC, 2012), derived primarily from

measurements at airports located near or within cities/towns, were used due to the long open fetch

characteristic of airport sites. Assessment of prevailing surface wind directions resulted in segregating the State

into 3 general areas: (1) the North, (2) the Southwest, and (3) the Southeast. The North is roughly bounded by

the US Interstate-80 and Highway 50 corridor and delineated as the area located north of 39o latitude (Figure 1).

Across this area, the prevailing winds are from the west during the spring, summer, and fall, but are more

complicated in the winter when winds come out of the north and south. South of 39oN, the southern half of the

State can be subdivided into two areas with the southeastern area having surface air flow from predominantly

the south in the spring, summer and fall; and winter air flow from primarily the west and north. The general

surface flow in the southwestern region is from the north. It is important to note that surface flow in this area of

complex terrain can vary throughout the day, may not coincide with synoptic and upper level flow patterns, and

will be influenced by local topography.

Based on the assessment of prevailing winds, sampling locations were chosen to include high elevation

and valley locations within each area. Most locations have a broad open fetch and sparse surface vegetation.

Most sites are in secure areas and have collaborating operators who regularly visit to perform routine checks

and maintenance.

During the first year of data collection, we assessed the results being obtained, the terrain features, and

the general wind patterns at each sites. Based on this information, new sites were added to the network.

Currently in each region of the State, we have both high elevation (> 2000 m) and valley locations. The latter

may be conduits for regional air transport from large urban centers that could provide both NOx and VOCs,

whereas the high elevation locations would be minimally influenced by surface transport of local pollution and

thus, provide an idea of the potential for free tropospheric inputs.

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Summary of past ozone concentrations reported for National Parks of the western U.S.

Burley and Ray (2007) collected data in select areas as a function of elevation at Yosemite

National Park in 2003 and 2005; however, these data were not collected simultaneously at all sites. The

highest concentrations during the night were measured at Crane Flat (65 to 79 ppbv, 2022 m). Crane

Flat data were collected on top of a lookout for a week. Burley and Ray (2007) suggested this location

was more exposed to the free troposphere. Based on meteorological analyses over a 5-day period,

Bao et al. (2008) suggested that 5 factors influence air movement in the Central Valley of California and

could be influencing air movement into Yosemite. These include (1) daytime low-level marine flow

through the Carquinez Strait into the Sacramento River delta; (2) daytime movement up and down the

San Joaquin Valley; (3) up slope (day time) and downslope (nighttime) flows; (4) a nocturnal low level

jet driven by geostrophic winds and the Coriolis Force; and (5) orographic eddies. Based on this list, to

understand these data, all these air masses need to be considered.

At Yosemite, surface winds (based on data collected in spring and summer 2010-2012) are

dominated by surface terrain flow patterns with air moving up the valleys from the south-southwest to

south-southeast during the day, and then down the valley from the east to east-northeast at night (see

Wright et al., 2014). Recent satellite data collected by NASA of the Rim Fire, August 22 and 26th,

showed that air at Yosemite may be transported from high elevation over the Sierras and into Nevada

(cf. NASA 2013). During the day, O3 concentrations measured at all locations by Burley and Ray (2007)

were not statistically significantly different and ranged from 50 to 60 ppbv. Burley and Ray (2007)

suggested this was due to deep vertical mixing. During the night, they suggested local topography was

influencing the observed values. The high values measured for Crane Flat at night reflect an inversion

over the Central Valley with the Crane Flat location sitting in a residual layer that has received pollution

from Modesto. Lower values were associated with valley locations measured at night by Burley and

Ray (2007) and were suggested to be due to the O3 being consumed by surfaces in areas of stagnant air

movement in the park. In the valleys the high convective mixing during the day is bringing free

tropospheric air to the surface, and then during the night this is consumed through reactions with

plant and lithogenic surfaces. Thus most of the O3 impacting the park is from the free troposphere

reflecting Asian contributions. This conclusion is similar to that reached by Wright et al. (2014) based

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on mercury measured using passive samplers from the Pacific Ocean to Great Basin National Park.

Based on Burley and Ray (2007) data collected at Turtleback Dome, a high elevation location that

overlooks Yosemite Valley, O3 concentrations at night were ~55 ppbv. These increased over the course

of a day by roughly 10 to 15 ppbv. This increased amount reflects an additional input from either the

Yosemite or Central Valley due to up valley flow.

Burley and Bytnerowicz (2011) reported O3 concentrations for the White Mountains of

California/Nevada for June to October 2009. Monthly mean concentrations were found to increase

with elevation. Based on the data presented mean concentration for 20 July to October was ~45 ppbv.

Data collected at two high elevation locations in 2011, showed hourly concentrations that ranged from

19 to 74 ppbv, and mean and median concentrations from July 20 to October 15 ranged from 51 to 54

ppbv (with >98% data coverage). Hourly mean and median values for these locations in 2012 (mean

and median 53 to 56 ppbv) were higher than those reported for the previous year with hourly

concentrations ranging from 12 to 78 ppbv (> 97% data coverage). It is noteworthy that

concentrations measured in Yosemite at the same locations above were also lower in 2011 (mean

values of 49 to 52 ppbv, and median values of 50 to 53 ppbv).

Burley and Bytnerowicz (2011) showed that O3 mixing ratios at the White Mountains valley site

(Owens Valley) location were the same as the high elevation locations during the day, however, valley

O3 decreased gradually overnight. This decrease can be attributed to reaction with surfaces that

occurred at a rate of 1.67 ppbv per hour going from 45 to 20 ppbv early in the morning. This increase in

O3 at the Owens Valley site increased with local sunrise as top down entrainment of free troposphere

air was mixed to the surface. This pattern was also used to explain observations of O3 at a location on

the eastern side of the Sierra Nevada Mountains just east of Reno during RAMIX (Gustin et al., 2013).

At this location, maximum values in CO, O3, and gaseous oxidized mercury were observed at 1100 to

1200 h corresponding with the time of maximum height of the mixed boundary layer. Based on the

data presented in Burley and Bytnerowicz (2011), top down entrainment resulted in daily increases in

air concentrations of ~4 to 8 ppbv/h depending on month. These values are similar to those measured

for 2011 during the NVROI. The highest values were observed during the day at the Crooked Creek site

(3088 m). This pattern can be attributed to the fact that this location is in a topographic bowl with

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some forest vegetation. As the winds calm down at night, an inversion would be established over the

small valley and O3 reacts with surfaces at this location.

In their time series plots (Burley and Bytnerowicz, 2011) showed distinct days with mean

concentrations of 55 to 65 ppbv that occur simultaneously at each high elevation sampling location.

These are also observed at the valley locations but are of lower concentration due to dilution of free

troposphere air with valley air. These events represent distinct polluted parcels of air coming into the

site from the free troposphere.

Detailed description of impacts of ozone on vegetation

Work in the 1980s that focused on the effect of Los Angeles pollution on local forests showed that jffrey and ponderosa pines were most sensitive (Miller et al., 1983). These are important species across western ecosystems. Earlier work by Miller et al. (1963) showed an average daily peak O3 concentration of 90 ppbv associated with stands of declining ponderosa pine. Takemoto et al. (1997) showed exposures of 40 to 60 ppbv could yield increased chlorotic mottle and premature senescence of Ponderosa Pine needles. The effective dose or commonly used threshold for causing either a reduction in growth or yield or visible injury is 40 ppb (cf. Cape, 2008).

The bi-weekly averages (48 to 72 ppbv) measured in the summer at Sequoia National Park that is

located on the eastern slope of the California San Joaquin Valley from May to November 1999

(Bytnerowicz et al., 2002) exceeded these values. Daily mean averages reported by Fine et al.

(submitted) for high elevations across Nevada and those measured in 2011 at Yosemite National Park

for 20 July to Oct 15th 2011 (Crane Flat--mean +/- standard deviation of 52 + 12 ppbv (median 53; range

10 to 83 ppbv, n=2073 hourly measurements with 39 missing>T-14-49 +/- 11 ppbv (median 49.5 range

11 to 77 ppbv, n= 1775 with 337 missing)> Tioga Pass-45+/- 8.5 ppv ( median 46; range 7 to 17 ppbv,

n= 2051 with 61 missing) also exceed the threshold value. The maximum values measured in Nevada

and at Yosemite are higher than reported in Burley and Ray (2007) that report data collected in 2003 to

2005. These data suggest that there are forest exposures of concern in the western United States.

Exposure to these concentrations would especially be a problem early in the growing season when

plants are physiologically active and their stomata are open (Panek and Goldstein, 2001). Overall

impacts on vegetation are a topic of discussion because increased CO2 may reduce the O3 effect by

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promoting stomata closure while increased nitrogen deposition may promote growth. However, more

recent work with Arabidopsis (common name: rockcress) has shown that chronic exposure decreases

photosynthesis, promotes early senescence, and reduces productivity (Ainsworth et al., 2012).

Ainsworth et al. (2012) pointed out the following in their review. Chronic exposure, unlike toxic

exposure, has been found to be irreversible and reduce the ability of stomata to respond to

environmental stimuli. Leaf age, plant development stage, and species influence the magnitude of the

effect. Drought exacerbates the effect because of the influence of O3 on stomata sensitivity to abscisic

acid. Thus, impacts could be greater in the western USA where drought is a common phenomenon.

Detailed description of each NVROI site

Peavine Peak (PEAV; 2515 m) is a prominent peak ~1000 m above the cities of Reno and Sparks,

which are located to the south (Figure 2). The sampling site is located above the tree line on the

summit. This concave mountain is located just east of the Sierra Nevada Mountains. There are two

peaks that are slightly higher to the west, Babbitt (2670 m) and Verdi (2574 m), in the Bald Mountain

Range. Beyond this range, the Sierra Nevada Mountains rise abruptly to similar elevations within 3.5

km (Figure 2).

The Nevada Agriculture Experiment Station farm (FARM) site is located on the east side of

Reno. This location is at the end of a topographic bowl that houses the Reno/Sparks metropolitan area.

This location receives air from the metropolitan area and the free troposphere (cf. Gustin et al., 2013;

Lyman and Gustin, 2009). The Central Valley of California, which is west of the Sierra Nevada

Mountains, could also contribute O3 and precursors to this area. Based on data collected in 2003,

Dolislager et al. (2012) suggested that Central Valley pollution was not generally transported to the

crest of the Sierras by way of intact air parcels, but could be lofted and lead to increased regional

background values. Traces of smoke from the recent American and RIM Fires show that direct input of

air from California to Nevada is possible (NASA, 2013). This air could impact surface sites across Nevada

with daytime mixing. The FARM was a location of a National Mercury Deposition Network site (MDN-

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NV-98) and has been the location of mercury research in the past (cf. Lyman et al., 2009 a and b; 2010;

Gustin et al., 2013).

Paradise Valley (PAVA) is located in the north center of a valley on a ranch where atmospheric

Hg, O3, and other criteria pollutants have been measured (cf. Lyman et al., 2008; Weiss-Penzias et al.,

2009). The valley is closed in by the Santa Rosa Mountains to the west and north, and the Hot Springs

Range to the east. Paradise Valley is connected to the I-80 corridor, and several large valleys to the

south that have mining and agricultural activities. Interstate 80 is to the south (~30 km) and is the

major trucking route crossing the State. Approximately 2000 to 3000 trucks move across the State per

day (NVDOT, 2011). The sampling site is located in an area of cleared pasture surrounded by

sagebrush, rabbit brush, and native grasses. In the local area there are small ranching operations that

grow alfalfa and raise cattle. These operations use diesel fuel and have wood stoves for home heating.

This site has been a National Mercury Deposition Network site (MDN-NV-02) for ~ 10 years. Data was

collected at Hinkey Summit (HISU) in the Santa Rosa Mountains for 4 weeks to compare with the data

collected simultaneously in PAVA. The HISU site was located above tree line on a flat graveled area on

the summit. This area was devoid of any significant vegetation and also housed a local communication

site.

South Fork State Recreation Area (SFRA) is a popular fishing area on the eastern side of the

State and the NVROI site is located adjacent to the park headquarters in an area managed by Nevada

State Parks employees. This site is located south of the town of Elko (population: 18000

(www.census.gov)) in the Huntington Valley. Just north of SFRA are the Diamond Mountains, to the

west are the Sulfur and Pinon Mountains, and to the east are the Ruby Mountains. The only local

impacts at this site may be periodic vehicle emissions. This location is sparsely vegetated with

sagebrush, rabbit brush, and grasses.

The Berlin Ichthyosaur State Park (BISP) location is perched on the west side of the Shoshone

Mountains that are a part of the Toiyabe Range. The sampling location is at 2082 m, sparsely vegetated

with native plants, and overlooks the Ione Valley. This site is managed by the employees of the Berlin

Ichthyosaur State Park. The sampling site is removed from the small campground area and main visitor

areas at the park. The nearest town is Gabbs, which in 2010 was reported to have ~270 people

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(www.census.gov). Given the connectivity of the valleys between the ranges from north to south, this

location could see some flow from line sources such as Highways (Hwy) 50 or 95 that are 80 km away.

Highway 50 in this area would have <100 trucks per day (NVDOT, 2011).

Warm Springs Summit (WSSU) is located on a bare hill above the summit of a pass that

connects Stone Cabin Valley and Hot Creek Valley. It is located at the southern end of the Hot Creek

Range. The site is situated above US Hwy 6, a lightly traveled road (~ 200 trucks per day; NVDOT, 2011),

and approximately 90 km east of the town of Tonopah that has ~2500 people (www.census.gov).

The Railroad Valley site (RRVA) is approximately 20 km east of Warm Springs Summit in the

center of a playa ~ 16 km away from Hwy 6. There is some minor oil extraction here. There is no

vegetation on the playa. Our instruments are co-located with an AErosol RObotic NETwork (AERONET)

sampling site operated by the University of Arizona and the National Air and Space Administration

(NASA). In addition, NASA conducts monthly flights from California to Railroad Valley in support of the

AJAX (Alpha Jet Atmospheric eXperiment) project. The jet does a vertical profile over RRVA and also

flies by WSSU and BISP (cf. Yates et al., 2013 ).

The White River Valley location (WRVA) is near the town of Preston (population < 100;

www.census.gov). The Egan Range bounds the valley to the east, and the White Pine and Monitor

Ranges are to the west. Highway 6 is north of the valley whereas Hwy 318 (~ 300 trucks per day;

NVDOT, 2011) runs along the valley. Small agricultural operations are present throughout the valley.

Great Basin National Park (GBNP) is located on the east side of the Snake Range. The sampling

location is in a forested area near the park headquarters in a slight topographic bowl. The general

location is at the confluence of two deep canyons. Air flow down these canyons will be influenced by

incident radiation. The UNR/Nevada Division of Environmental Protection air sampling trailer is co-

located with the IMPROVE (Interagency Monitoring of Protected Visual Environments) and CASTNet

(Clean Air Status and Trends Network) sites. The site has pinyon/juniper forest vegetation.

Echo Peak (ECPK) is located on the Nevada Nuclear Security Site. This remote site is situated on

a cleared hill surrounded by pinyon-juniper forest, on the southern edge of a broad plateau. This site is

operated in cooperation with the USA Department of Energy.

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The Cathedral Gorge State Park (CGSP) site is operated by Nevada State Parks employees. This

site is situated above Meadow Valley Wash in the Meadow Valley. This site is on a small ridge within a

topographic bowl that is bounded by the Bristol, Highland, and Chief Ranges to the west, the Clover

and Delamar Mountains to the south, and rolling hills that make up the border with Utah to the east.

The O3 monitor is situated on a small ridge within Meadow Valley. The main park lies to the west, Hwy

93 is to the east, and a small agricultural operation is directly south. Meadow Valley Wash drains to

the south and eventually ends up at Lake Mead, the source of water for Las Vegas. This location is

topographically connected to Las Vegas by way of a surface pathway that would pass air from Las

Vegas over Lake Mead, and then up Meadow Valley Wash. Alternatively, air could move north out of

Las Vegas up the Dry Lake Valley then up the Meadow Valley Wash. Caliente, the town directly to the

south of the park, has a population of ~1200 (www.census.gov). Approximately 300 trucks per day

travel on Hwy 93 (NVDOT, 2011).

The Pahrump (PRMP) site is located on private property ~10 miles north of the town of

Pahrump. This location is separated from Las Vegas (population 2 million) by the abrupt Spring

Mountains that host the Mount Charleston Wilderness Area and Mount Charleston Peak (3632 m). The

population of Pahrump is 37000 (www.census.gov, visited 4/4/2013). This site is sparsely vegetated

with well-developed desert pavement.

Angel Peak (AGPK; 2682 m) is 45 km northwest of Las Vegas (~900 m) on the eastern slope of

Mount Charleston (3632 m). This location is situated on top of a bare peak and surrounded by a low

density pinyon pine forest.

Methods

Details on ozone measurements

During the first year of the field campaign, our method detection limit for O3 averaged 2.5 ppbv

(range of 1.5 to 3.4 ppbv) at the four POMS sites and was 0.3 ppbv (Teledyne 400E) and 3.5 ppbv

(Thermo 49i) for the analyzers in operation at Paradise Valley. At the four POMS sites, average

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precision was 3.9% (range of 1.3 to 6.2%) and mean bias was 3.4%. For Paradise Valley, average

precision was 5.0% and bias was ±3.8%.

At these 5 sites, multi-point calibration checks of the analyzers were performed at initial set up, at

approximate 6 month intervals, and after any significant maintenance. Automated daily zero checks

were performed at the POMS sites (BISP, WRVA, SFSR, and CGSP) using a solenoid switch that routed

the sampling stream from ambient air to zero air (ambient air passed through an external Hopcalite

scrubber) for 15 minutes each day. The monthly mean of these daily zero checks ranged from -3.3 to

1.0 ppbv. The sampling height at all sites was 3 to 4 meters above the ground. At the POMS sites, an

empty, downward facing filter holder was attached to the inlet to prevent bugs and large debris from

entering the sampling line. The sampling line consisted of 0.635 cm (outer diameter) Teflon tubing.

The total length of the sampling line was approximately 2 m. The sample stream was routed through a

particulate filter (5.0 µm Millipore Mitex™ Membrane Filter) approximately 1.5 m from the inlet. From

the particulate filter, a short run of sampling line directed the sample stream to the inlet of the

analyzer. At Paradise Valley, the O3 analyzer was housed within a climate controlled sampling shelter.

The sampling inlet was mounted approximately 1.5 m above the roof of the trailer and protected with

a plastic rain shield. Ambient air was routed to the analyzer via Teflon sampling lines and a glass

manifold. The sample stream passed through a particulate filter located between the manifold and the

analyzer. The total length of the sampling line was less than 3 m. Particulate filters were changed

every 4 to 6 weeks by on-site operators from cooperating agencies or cooperating private land-owners.

Sampling lines, analyzer pumps, external O3 scrubbers, and analytical O3 scrubbers were changed every

six months at each site. Bug screens, rain shields, and the glass manifold at Paradise Valley were

cleaned at least every six months. At the ECPK and PEAV sites, the O3 analzyers were housed in climate

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controlled communication buildings maintained by external agencies. Dedicated sampling lines were

routed outside of these shelters to elevated, protected intakes. A Teflon filter was positioned at

instruments’ inlets. At the shelter-based sites, intake screens, sampling lines, and O3 scrubbers were

changed or cleaned every six months.

The FARM site O3 analyzer was housed in a temperature controlled air sampling shelter and the

inlet was at 4 m above ground and 1 m above the roof. A Teflon® filter was attached to the instrument

inlet and replaced bi-weekly.

A POMS unit, which was used at Hinkey Summit during an elevation transect in the spring, was co-

located in Paradise Valley adjacent to the monitoring shelter. Nine hours of O3 measurements were

collected simultaneously by the 2B Technologies M205 instrument in the POMS unit and the Thermo

49i instrument in the monitoring shelter. Concentrations measured by the Thermo 49i instrument

were an average (± s) of 4.5 ± 0 ppbv lower than that measured by the 2B Technologies M205

instrument.

Hourly data, calculated from 1 min averages, were retrieved from the POMS sites via satellite

modem. Ozone data from these sites were accepted as valid if the concentration was between 0 and

500 ppbv (the calibrated range of the instrument), measurements were available for at least 75% of

the hour, instrument volumetric flow was at least 1.2 Lpm, and data was bracketed by valid zero and

calibration checks (semi-annual). Fifteen minute data from PAVA was internally logged by the

instrument then manually downloaded approximately every 6 weeks. Hourly data was computed from

the logged 15 minute data.

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The 2B Technologies instruments were calibrated using a 2B Technologies M306 O3 calibration

source. The M306 calibration sources were calibrated at the factory using a NIST-traceable O3

standard. The Thermo and Teledyne instruments deployed at Paradise Valley were calibrated using a

Teledyne API 700E dynamic dilution calibrator and Teledyne API 701 zero air generator. In past field

campaigns, the performance of the Teledyne API 700E was verified with a transfer standard at Washoe

County Health Department. The performance of the 700E was verified prior to field deployment for

this campaign using a Thermo 49C as a working standard. The Thermo 49C had been calibrated at

Washoe County Health Department using a NIST-traceable transfer O3 standard. As a secondary check,

the performance of the 700E was also verified using a Thermo 49i as a working standard. In this

capacity, the Thermo 49i had been calibrated in our lab using a Teledyne API 700U dilution calibrator

that was calibrated with a NIST-traceable O3 standard at the Teledyne API factory the month prior. In

both tests, multi-point concentrations of O3 generated by the 700E were within 5% of the working

standards. By conducting multiple comparisons between instruments and calibrators, we sought to

ensure that the performance of all operational instruments were verified and NIST traceable.

Precision and bias were calculated with the EPA’s Data Assessment and Statistical Calculator

(http://www.epa.gov/ttn/amtic/qareport.html) using the routine multi-point calibration checks at

each site. The detection limit of the analyzers deployed at each site was estimated by multiplying the

standard deviation of the annual mean of the routine blank checks by two. 2B Technologies reported a

detection limit of 2 ppbv for the M205 O3 analyzers.

Details on co-located measurements

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On several occasions, instruments were co-located to compare the consistency of

measurements. At Paradise Valley, a 2B Technologies instrument was deployed alongside the Thermo

instrument for 38 days (1/18/2013 – 1/23/2013 and 2/14/2013 – 3/14/2013). The 15 minute average

O3 concentrations measured by the Thermo 49i were an average of 2.0% less (± 6.0%, n = 3163) than

the 2B Technologies M205 analyzer. The mean absolute difference (0.6 ppb) was within the

manufacturer-stated instrument precision (± 1.0 ppb).

At GBNP, a Teledyne 400E and a 2B Technologies M211 (Interference free model) O3 analyzer

were installed in the UNR/Nevada Division of Environmental Protection air sampling trailer which is

adjacent to the CASTNet trailer that houses the O3 monitor operated by the National Park Service

(NPS). The instruments were co-located for 27 days (4/11/2013 – 5/07/2013). Comparing 1 h mean O3

concentrations, the 2B Technologies M211 analyzer reported 7.7% (± 1.4 %, n = 585) higher ambient

concentrations than the CASNET reported O3 concentrations Teledyne 400E. However, this difference

is attributable to a disparity in the calibration factors of each instrument, with the 2B Technologies

M211 reporting 7.8% higher recovery than the 400E during calibration span checks (400 ppb O3) in

clean interferent-free air. The comparability of the two measurements, when adjusted for the

calibration offset, indicates that measurements at GBNP are not significantly impacted by ambient O3

interferents. The NPS O3 analyzer at GBNP, during this same time period, reported mean O3

concentrations that were 0.5 ppb (1.0 ± 5.6 %, n = 577) higher than the mean concentration measured

by the 2B Technologies M211. This difference in O3 concentrations is not statistically significant (2-

sample t-test, p = 0.166, α = 0.05).

Details on meteorological measurements

The meteorological measurements at the POMS sites were made with a Climatronics All-In-One

sensor which employs a sonic anemometer for wind measurements. These sensors were factory

calibrated prior to field deployment. They have no moving parts and require minimal power to

operate, making them well suited to deployment at rural, solar powered monitoring sites. One hour

averages, calculated from one minute data, were retrieved from the POMS data loggers via satellite

modem. Meteorological data was accepted as valid if it fell within the operating range reported by the

manufacturer: 0 to 50 m/s for wind speed; 0 to 359.9° for wind direction; -40 to 55°C for temperature;

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and 0 to 100% for relative humidity. The sigma theta of wind direction was accepted as valid if a valid

wind direction measurement was obtained for the hour. The performance and calibration of the

Climatronics sensors was verified at the factory within 4 months prior to field deployments.

At Great Basin, Paradise Valley, Echo Peak, and Peavine Peak, wind speed and direction were

measured using an RM Young AQ wind sensor (model 05035) that uses a helicoid propeller to measure

wind speed and a lightweight vane to measure wind direction. The calibration of the wind sensor was

verified using an anemometer drive to simulate wind speed at five points across the operational range.

A Campbell HMP45C probe was used for temperature and relative humidity measurements. Solar

radiation was measured at Paradise Valley using a Licor li1200x solar pyranometer. Additional

meteorological data from Great Basin National Park was downloaded from the National Park Service

Gaseous Pollutant and Meteorological Data website (http://ard-request.air-resource.com/data.aspx).

Barometric pressure was measured at Echo Peak and Peavine Peak from the beginning of site

operation, at Paradise Valley from January 2013 (Vaisala PTB110), and at Great Basin beginning in March

2012. Barometric pressure measurements were intermittent at Great Basin National Park and

unavailable at Paradise Valley during the first year of the field campaign. Pressure data from nearby

locations was obtained from the National Climatic Data Center to supplement the data sets for these

locations. Supplemental pressure data for Paradise Valley was from the Winnemucca Airport (80 km

south; 1313 m asl, 40.8967° N 117.8058° W) whereas supplement data for Great Basin National Park

was from Yelland Field in Ely, NV (~105 km west; 1908 m asl, 39.3016° N 117.8058° W). At FARM,

meteorological data are available from a Western Regional Climate Center (WRCC) site (1330 m asl,

39.5030˚N, 117.7378˚ W) 1 km southwest of the sampling site. Various sensors (including solar

14

radiation, wind speed, wind direction, air temperature, soil temperature, relative humidity, dew point,

pressure, and precipitation) are set at appropriate heights (e.g. 3 m for the wind sensor).

Specific calculations

To aid in the direct comparison of meteorological conditions among sites, local station

atmospheric pressure was converted to mean sea level pressure following the weather reporting

conventions at Lawrence Livermore National Lab

(http://www-metdat.llnl.gov/cgi-pub/faq.pl#pressure) where Mean Sea Level Pressure (MSLP) and

Station Pressure (SP) are in mB and site elevation (SE) is in m (Equation SI 1):

Equation SI 1: MSLP = SP/ ((288 – 0.0065*SE)/288)^5.256)

The Pasquill-Gifford (PG) atmospheric stability class was calculated using the sigma theta of

wind direction, wind speed, and time of day following the procedure described in the EPA’s

Meteorological Modeling Guidance for Regulatory Modeling Applications report available at

http://www.epa.gov/scram001/guidance/met/mmgrma.pdf. This procedure can provide a general

picture of stability conditions when meteorological measurements are limited. The Pasquill-Gifford

stability class was calculated at the four POMS sites and Great Basin National Park. Sigma theta of

wind direction was not logged at Paradise Valley and as a result, this calculation was not possible for

that location. With the exception of a handful of days, this procedure predicted neutral atmospheric

conditions at our site locations. There was not any significant diel or season pattern detected following

this procedure. Given the complex terrain and arid climate, neutral conditions seem unlikely and thus

this method may not be useful for calculating stability in this setting. Other measurements are

necessary to accurately determine atmospheric stability conditions at these field sites.

Dew point temperature was calculated using ambient air temperature and relative humidity

following the method described by the NOAA National Weather Service Forecast Office

(http://www.srh.noaa.gov/epz/?n=wxcalc). Following Weiss-Penzias et al. ( 2006), water vapor was

calculated in g/kg using RH (relative humidity) in percent, BP (station barometric pressure) in mB,

Temp (ambient air temperature) in degrees Celsius (Equation SI 2):

15

Equation SI 2: Water vapor = 38.02*(RH/BP)^((Temp*17.67)/(Temp + 243.5))

Data analyses

Monthly grids and time series plots were compiled for O3 and meteorological parameters for

each monitoring site in Microsoft Excel 2011. Regression, correlation, comparison of means, and

ANalysis Of VAriance (ANOVA) were computed using Minitab® 16 statistical software.

Ozone data were normalized by subtracting the site monthly mean from the site daily mean.

This was intended to remove the site specific and seasonal bias and allow for direct comparison of O3

between sites. To evaluate the role of local, surface meteorology on observed ozone, average

meteorological parameters associated with periods of elevated ozone (> 90th percentile of normalized

O3 for each season) were compared to average conditions for the season at each site.

Results

Site specific meteorology

Highest seasonal mean (± s; seasonal maximum) wind speeds occurred in the spring at South

Fork State Recreation Area (3±2 m/s; 10m/s), Berlin Ichthyosaur State Park (5±3 m/s; 29m/s), and

Cathedral Gorge State Park (4±3 m/s; 21 m/s) (SI Table 1). Paradise Valley recorded the highest

seasonal mean wind speeds in the spring (3±2 m/s; 12 m/s) and summer (3±2 m/s; 8 m/s); despite

similar means, wind speeds were statistically significantly (p = 0.04) greater in the spring than the

summer at Paradise Valley. The seasonal mean wind speed at Great Basin National Park was consistent

(3±1 m/s) in the summer, fall, and spring; however, wind speed was statistically significantly (p = 0.00)

lower in the fall than the spring and summer (not significantly different, p = 0.45). Of the high

elevation sites (>2000 m), wind speed was statistically significantly greater (p = 0.00; 95% CI = 1.38 to

1.51 m/s) at Berlin Ichthyosaur State Park than at Great Basin National Park. This is likely reflective of

site characteristics. The monitoring site at Berlin Ichthyosaur State Park has low shrub vegetation

whereas the site at Great Basin National Park is surrounded by pinyon-juniper forest which would

temper wind speeds by introducing more frictional force due to the presence of greater surface

roughness (Whiteman, 2000).

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Over all seasons at the low elevations (<2000 m), wind speed was significantly (p = 0.00)

different between sites with the fastest wind speeds occurring in the following hierarchy: White River

Valley > Cathedral Gorge State Park > Paradise Valley > South Fork State Recreation Area. Cathedral

Gorge State Park and White River Valley are characterized by low shrub habitat and subject to rapid

surface heating that likely promotes thermally driven up-valley and down-valley winds at these

locations (Whiteman, 2000). Surface heating, and thus thermally driven winds, are tempered at the

Paradise Valley and South Fork State Recreation Area due to higher densities of surface vegetation

(Houghton et al., 1975). At South Fork State Recreation Area, a large reservoir (4.8 km long x 0.8 km

wide) is located to the west of the monitoring site and extends to northwest and southeast of the site.

At Paradise Valley, agricultural operations create generally more verdant land cover when compared to

other low elevation sites. These features, an adjacent body of water and verdant landscape, temper

changes in ambient air temperature as a result of weaker sensible heat fluxes (Whiteman, 2000) and

subsequently moderate wind speed.

Terrain driven diel wind patterns were apparent at all sites during the spring and summer

(Figure SI 1). At Paradise Valley, up-valley winds dominated during the day with nighttime flow

predominately resulting from mountain drainage flow out of the Santa Rosa Mountains located at the

northwest end of the valley. At South Fork State Recreation Area, the large reservoir to the west of the

monitoring site led to a dominant lake breeze during daylight hours. At night, the drainage out of the

Ruby Mountains located to the southeast of the site was channeled up the broad Huntington Valley,

south of the site, leading to a predominant south wind. Drainage out of the Sulphur Springs Range to

the southwest of the site was also common.

At Great Basin National Park, a predominant southwest wind was present throughout day and

night hours. To the west of the site is the Snake Range with multiple peaks extending more than 3000

m high. The Baker Creek drainage extends from Baker Lake, a glacial cirque on the east side of the

crest, down the east slope of the range and represents a likely transport corridor for air. The general

orientation of the Baker Creek drainage is consistent with the wind direction measured at the site. The

monitoring site at Berlin Ichthyosaur State Park is located on a plateau extending out into a wide valley

that is oriented southwest to northeast. Up-valley winds dominated daytime flow and down-valley

17

winds were dominant at night. Cross-valley flow was also present, primarily during transition hours

around sunset and sunrise.

The upper end of White River Valley is oriented in a northwest to southeast direction and the

length of the valley runs north to south. Up-valley flow was also predominant during the day at White

River Valley and down valley flow from the upper end of the valley was present at night. Winds from

the northeast occurred for a few hours after sunrise. This would be consistent with rapid heating of

the eastern slope causing upslope flow to dominate at this time. Winds at Cathedral Gorge State Park

are characterized by up-valley flow during the day and down-valley flow at night.

Seasonal meteorology

Wind direction was variable during the fall and winter at the northern low elevation sites

(Paradise Valley and South Fork State Recreation Area) which likely reflected the presence of frequent

inversions setting up in the valleys that slowed surface wind speeds and moderated the influence of

the surrounding terrain. At Great Basin National Park, winds were consistent across seasons where

data was available. Northeast winds occurred for a few hours after dawn, which would be consistent

with upslope flow then southwest winds during the day. At night, flow was mostly from the southwest

suggesting that the consistent influence of gravitational settling of air masses promotes downslope

mountain drainage flows. At Berlin Ichthyosaur State Park and White River Valley, daytime winds were

variable but with a dominant flow from the north. At Berlin Ichthyosaur State Park, downslope flow

from the Shoshone Mountains and Toiyabe Range to the east and northeast was dominant at night.

Nighttime winds at White River Valley were similar across all seasons with a mostly northwest flow.

The direction of wind flow at Cathedral Gorge State did not differ markedly between seasons (Figure SI

18F). Unlike other sites in the NVROI, this site rarely sees snow cover and would be less prone to

developing persistent winter time inversions, thus allowing connectivity with surrounding terrain to be

maintained during all seasons.

Across all sites, temperatures were lowest in the winter (mean ± s ranged from -3 ± 8°C to 2 ±

5°C), gradually increased through the spring (8 ± 9°C to 13 ± 8°C), reached a maximum in the summer

(18 ± 8°C to 25 ± 6°C), and declined in the fall (1 ± 6°C to 15 ± 8°C) (Table SI 4). Of the low elevation

sites, the highest mean and maximum temperatures were at Cathedral Gorge State Park (25 ± 6°C;

18

37°C) whereas Paradise Valley generally had the lowest mean and minimum temperature (-2 ± 7°C; -

21°C). At the high elevation sites, mean and maximum temperatures were similar with Great Basin

National Park experiencing slightly warmer temperatures than Berlin Ichthyosaur State Park during the

spring and summer months.

Relative humidity was highest during the winter (mean ± s ranged from 44 ± 22% to 64 ± 21%)

and lowest during the summer (20 ± 14% to 31 ± 21%). At the low elevation sites, the northern sites

were generally more humid than the southern sites. On a seasonal basis, relative humidity was similar

at the high elevation sites (Table SI 4).

Seasonal mean dew point temperature ranged from -12 ± 6 to 2 ± 7°C with lowest dew point

temperatures occurring during the spring and the highest during the winter (Table SI 13). Past studies

have used dew point temperature as a means to elucidate the sources of air masses contributing to

observed ozone concentrations (Fishman et al., 1987).

Across all sites, seasonal mean water vapor concentrations (± s) ranged from 2.2 ± 1.0 to 5.0 ±

3.2 g/kg with the lowest concentrations measured during the winter and the highest during the

summer (Table SI 13). Mean concentrations were generally lower at the high elevation site (BISP) than

at the low elevations sites. These calculated concentrations and seasonal trends are consistent with

those reported by Ambrose et al. (2011) for Mt. Bachelor Observatory (2763 m asl) in Oregon (2.4 to

5.8 g/kg), which is frequently impacted by free tropospheric air. This suggests that water vapor, used

in coordination with measurements of other pollutants, may be useful in segregating the influence of

the free troposphere and the boundary layer during periods of enhanced ozone at NVROI sites.

Station pressure was measured at four sites and converted to mean sea level pressure in order

to compare sites at various elevations. Mean sea level pressure was similar at all sites across three

seasons and was slightly higher at the high elevation site (BISP was 1021 ± 4 mB versus ~1018 ± 3 to 4

mB at the lower elevation sites) in the summer (Table SI 4). Because cold air is denser than warm air,

the slightly higher pressure at high elevation sites could be a result of slightly cooler temperatures at

the high elevation site compared to the low elevation sites.

19

Detailed assessment of ozone concentrations and meteorological conditions during elevated O3

concentrations

The influence of meteorology on elevated O3 concentrations (Daily normalized mean > 90th

percentile normalized O3 concentrations) was evaluated seasonally at each site. In the summer, during

days with elevated O3 concentrations, wind speed was significantly (p ≤ 0.02) higher than average at

BISP, GBNP, and SFSR. Relative humidity was significantly (p ≤ 0.05) lower than average at BISP, GBNP,

WRVA, and CGSP whereas water vapor and dew point temperature were significantly lower (p ≤ 0.06)

at all sites where O3 data were collected throughout the summer months (i.e. all sites except for

PAVA). This suggests that O3 concentrations were enhanced at the high elevation and northern valley

sites as a result of transport. At the other sites where wind speed was not significantly different on

enhanced O3 days, vertical transport may be important and would not be adequately captured by

single point measurements of wind speed. The lower relative humidity associated with enhanced O3

days at the high elevation and southern valley sites suggests that convective surface heating, which

would be more efficient under lower humidity conditions and would promote vertical mixing as well as

horizontal transport, contributed to enhancing observed O3 at these sites. Prior studies in the west

(Ambrose et al., 2011; Weiss-Penzias et al., 2009), and in Florida (Gustin et al., 2012), have suggested

that decreasing water vapor is associated with intrusion of air from the free troposphere. The

negative relationship of O3 with dew point and relative humidity is further suggestive of input from the

free troposphere (cf. Weiss-Penzias et al., 2009; Gustin et al., 2013).

In the fall, meteorological variables on days with enhanced O3 were generally consistent with

average conditions across sites with a few exceptions: relative humidity, water vapor, and dew point

temperature were significantly (p ≤ 0.03) lower than average at BISP; and barometric pressure was

significantly (p = 0.04) lower at CGSP. Upper level winds influencing Nevada generally take a more

westerly approach beginning in the fall. Therefore, Berlin Ichthyosaur State Park, which is the most

westerly high elevation site in the network, could be intercepting free tropospheric air masses in

isolation. Thus, these air masses intercepted at Berlin Ichthyosaur State Park had consistently lower

water vapor, dew point, and relative humidity, but as they continue across the State, surface friction

and gravity waves associated with complex terrain disrupt geostrophic transport and dilute the

20

characteristics of these air masses. Thermal lows are frequently centered in the southern part of the

State, where Cathedral Gorge is located. This synoptic pattern would tend to be to bring in regional

pollution.

Local meteorology was significantly different than average on winter days with elevated O3. Wind

speed was significantly (p ≤ 0.05) higher at low elevation sites, indicating that transport promotes

higher O3 concentrations. Temperature was significantly higher than average at the northern valley

sites which could indicate that local photochemical production is important; however, when coupled

with associated higher wind speeds, the positive association between temperature and O3 could

support the role of convectively driven transport (vertical or horizontal).

Similar to fall, meteorological variables on days with enhanced O3 during the spring were generally

consistent with average conditions across sites with a few exceptions: wind speed was greater than

average (p ≤ 0.07) at CGSP and PAVA; temperature was greater than average (p = 0.07) at GBNP;

relative humidity was lower than average at BISP, GBNP, SFSR, and PAVA (p ≤ 0.14), water vapor and

dew point temperature were lower than average at BISP and PAVA (p ≤ 0.11). The lower dew point

temperature and water vapor concentrations coincident with elevated O3 at the westernmost sites

(BISP and PAVA), further suggest that these sites are intercepting undiluted air derived from the free

troposphere, the properties of which will be altered as air parcels are subject to surface friction and

vertical mixing while traversing the State.

Calculation of the W126 cumulative exposure index.

The W126 index was calculated by sigmoidal weighting. “The sigmoidal weighting function is of the

form:

where: M and A are arbitrary positive constants

wi = weighting factor for concentration ci

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ci = concentration i (in ppm)

The arbitrary positive constants M and A are 4403 and 126 ppm-1, respectively. Their values were

subjectively determined to develop a weighting function that (1) focused on hourly average

concentrations as low as 0.04 ppm, (2) had an inflection point near 0.065 ppm, and (3) had an equal

weighting of 1 for hourly average concentrations at approximately 0.10 ppm and above.

The name for the W126 exposure index was derived from the following:

"W" was associated with the word "weighted" and;

The number "126" was associated with the 126 value of the constant "A" in the W126 equation (see

above).” (http://www.asl-associates.com/w126.htm)

22

SI Table 1: Seasonal summary of meteorological parameters for six sites within the Nevada Rural Ozone Initiative Network for July 2011 to June 2012. The abbreviations in the table correspond to the following parameters: WS (wind speed); T (temperature); RH (relative humidity); and MSLP (mean sea level pressure).

23

(A) Paradise Valley

(B) South Fork State Recreation Area

(C) Great Basin National Park

(D) Berlin Ichthyosaur State Park

(E) White River Valley

24

(F) Cathedral Gorge State Park

Figure SI 1: Seasonal surface winds measured at six sites within the Nevada Rural Ozone Initiative Network during the first year of measurements. Wind roses are presented by season beginning with spring (March to May 2012) on the left, then summer (July to Aug 2011 and June 2012), then fall (Sept to Nov 2011), and winter (Dec 2011 and Jan to Feb 2012) on the right. Winter wind data was not available for Great Basin National Park (Figure 1C). The color key below figures A to F provides the range of wind speeds (m/s) corresponding to the colors on the wind roses.

25

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Webpages

(http://www.epa.gov/ttnchie1/net/2008inventory.html)

(http://www.wrcc.dri.edu/fire/tidbits.html

www.census.gov, visited 4/4/2013

http://www.epa.gov/ttn/amtic/qareport.html

http://ard-request.air-resource.com/data.aspx

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http://www.epa.gov/scram001/guidance/met/mmgrma.pdf

http://www.srh.noaa.gov/epz/?n=wxcalc

http://www.asl-associates.com/w126.htm

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