### Journal of Environm ental Monitoring



## Baseline ambient gaseous ammonia concentrations in the Four Corners area and eastern Oklahoma, USA

Mark E. Sather * a , Johnson Mathew b
, Nghia Nguyen b
, John Lay b
, George Golod b
, Robert Vet c , Joseph Cotie d
, Terry Hertel d
, Erik Aaboe d
, Ryan Callison e , Jacque Adam e , Danielle Keese e , Jeremy Freise e , April Hathcoat e , Brenda Sakizzie f
, Michael King f
, Chris Lee f
, Sylvia Oliva g , George San Miguel g , Leon Crow h and Frank Geasland h

a

Air Quality Analysis Section, U.S. Environmental Protection Agency (EPA) Re gion 6, 1445 Ross Avenue, Dallas, TX 75202, USA b Houston Laboratory, U.S. EPA Region 6, 10625 Fallstone Road, Houston, TX 77099, USA
c Environment Canada, Air Quality Research Divi sion, 4905 Dufferin Street, Toronto, Ontario, Canada M3H 5T4 d

New Mexico Environment Department, 1301 Si ler Road Building B, Santa Fe, NM 87507, USA
e Cherokee Nation Environmental Programs, 208 E. Allen Road, Tahlequah, OK 74464, USA f

Southern Ute Indian Tribe, Air Quality Program, P.O. Box 737, Ignacio, CO 81137, USA gMesa Verde National Park, Natural Resources, Mesa Verde, CO 81330, USA h Quapaw Tribe of Oklahoma, P.O. Box 765, Quapaw, OK 74363, USA Received 12th May 2008 , Accepted 11th September 2008 First published on the web 25th September 2008

Ambient ammonia monitoring using Ogawa passive samp lers was conducted in the Four Corners area and eastern Oklahoma, USA during 2007. The resulting data wi ll be useful in the multipollutant management of ozone, nitrogen oxides, and visibili ty (atmospheric regional haze) in the Four Corners area, an area with growing oil/gas production and incr easing coal-based power plant c onstruction. The passive monitoring data also add new ambient ammonia concentration inform ation for the U.S. and will be useful to scientists involved in present and future visibility modeling ex ercises. Three week integrated passive ammonia samples were taken at five sites in the Four Co rners area and two sites in eastern Oklahoma from December, 2006 through December, 2007 (January, 2008 for two sites). Results show significantly higher regional background ammonia concentr ations in eastern Oklahoma (1.8 pa rts per billion (ppb) arithmetic mean) compared to the Four Corners area (0.2 ppb arithmetic mean). Annual mean ammonia concentrations for all Four Corners area site s for the 2007 study ranged from 0.2 ppb to 1.5 ppb. Peak ambient ammonia concentrations occurred in the spri ng and summer in both area s. The passive samplers deployed at the Stilwell, Oklahoma site compared favor ably with other passive samplers and a continuous ammonia monitoring instrument.



### 1. Introduction In late 2005 the Four Corners Air Qualit yTask Force (FCAQTF) was formed to address air qualityissues Journals Journal of Environmental Monitorin g Advance Articles DOI: 10.1039/b807984 f J. Environ. Monit. , 2008 DOI: 10.1039/b807984f Pa p e r Page 1 of 11 Baseline ambient gaseous ammonia concentrations in the Four Corners area and ea..... (DOI: 10.1

...

9/30/2008 htt p ://www.rsc.or g /delivery/

_

ArticleLinkin g /ArticleLinkin g .cfm?JournalCode=EM&Year=2008&

...associated with growth in the oil/gas pr oduction and coal-fired power plant industries. 1 The Four Corners area includes southwest Colorado, northwest New Mexi co, southeast Utah, and nor theast Arizona. One of the concerns of the FCAQTF is that ambient ozone con centrations in the area may not meet the new U.S. 8 hour ozone standard of 0.07 5 parts per million (ppm). 2 In order to mitigate in creases in ambient ozone concentrations, certain controls ar e being considered for the ozone precursor nitrogen oxides, such as selective and non-selective catalytic reduction on o il and gas production equipment and power plants. The use of selective or non-sel ective catalytic reduction controls would, however, result in the release of more ammonia emissions to the atmosphere. Ammonia is know n to be a precursor of fine particulate matter, 3 which adversely affects public health, atmosphe ric visibility, and aci d deposition patterns. 4 Currently, it is not known whether or not increased ammonia emissions in the Four Co rners area would be significant enough to cause a degradation in atmo spheric visibility. To enable air quality managers to answer this question in the future, ambient monitoring of gaseous ammonia (NH 3 ) was instituted to set a current baseline. Then in the future, after nitrogen oxide c ontrols have been implemented along with any gaseous ammonia increases due to growth in other source s such as population and mobile vehicles, ambient monitoring of gaseous NH 3 can take place again to compare to th e current baseline. Thus, the states of New Mexico and Colorado in the Four Corners area requested to work with the U.S. Environmental Protection Agency (EPA) Region 6 in 2006 in order to obtain a current ambient ammonia monitoring baseline. To keep costs low Ogawa passive sampling devices (PSDs) were depl oyed for the baseline study, and the U.S. EPA Region 6 laboratory in Houston, Te xas, provided the laboratory preparation and ion chromatographic (IC) analytical work. Simple to use PSDs, includi ng the Ogawa PSD, have been successfully used in many published ambient ammonia stud ies around the world. 5

– 15 The U.S. currently lacks a routine national Federal Reference Method (F RM) ambient monitoring network for ammonia, so the data from the 2007 study in th e Four Corners area and eastern Oklahoma also add new ambient ammonia concentration information for the U.S., adding to previous ambient ammonia monitoring data collected in eastern, western, and southeastern U.S. states. 14

– 19 

### 2. Experimental 2.1 Study sites There were six passive ammonia sites that sampled for the entire year-long study. In addition, in response to the Quapaw Tribe's interest in obtaining ambi ent ammonia concentrations around a nearby mushroom processing facility, a sevent h site participated in th e study for the last eight 3 week integrated sampling periods. A map of all study s ites from the three different ar eas, including annual mean ammonia concentrations for the six sites thatoperated year-long, is depicted in Fig. 1 . A variety of site types was desired and included: regional backgr ound sites in both the Four Corner s area (Mesa Verde National Park) and eastern Oklahoma (Stilwell); oil and gas development impacted sites in the Four Corners area (Navajo Lake and Southern Ute). The Southern Ute site wa s also impacted by mobile source emissions, being nearby a major highway; a coal-fired power plant impact ed site in the Four Corners area (Substation); an urban site in the Four Corners area (Farmington Airport), and finally a ne arby source oriented site situated to record higher ambient ammonia concentratio ns (Quapaw site in northeastern Oklahoma). Page 2 of 11 Baseline ambient gaseous ammonia concentrations in the Four Corners area and ea..... (DOI: 10.1

...

9/30/2008 htt p ://www.rsc.or g /delivery/

_

ArticleLinkin g /ArticleLinkin g .cfm?JournalCode=EM&Year=2008&

...2.2 Field instrumentation For the passive ammonia sampling, Ogawa passive sa mpling devices (PSDs) were used, previously obtained from Ogawa & Co., Inc., Pompano Beach, Flor ida. The Ogawa PSD is composed of a solid c y lindrical pol y meric body(two centimetres b ythree centimetres lon g ) with a diffusion barrier and two Fig. 1 Map of the 2007 passive ammonia monitoring sites and annual mean concentrations in the Four Corners area and eastern Oklahoma. Page 3 of 11 Baseline ambient gaseous ammonia concentrations in the Four Corners area and ea..... (DOI: 10.1

...

9/30/2008 htt p ://www.rsc.or g /delivery/

_

ArticleLinkin g /ArticleLinkin g .cfm?JournalCode=EM&Year=2008&

...stainless steel screens on each side . At most of the sites the ammoni a PSDs were mounted on aluminium pole assemblies about 1.5 metres above ground level (agl). A few of the sites installed the aluminium pole assemblies on top of existing air monitoring sampling tr ailers (about 5 metres agl). Each PSD was placed under a rain shelter for wind face velocity and precipitation protection. Gaseous ammonia, upon natural diffusion into the PSD, was collected on filters coated with citric acid. Th e filters used in this study were purchased from Ogawa by the New Mexico Environmen t Department, the Cherokee Nation, and the U.S. EPA Region 6 laboratory in Houston. The detection limit of the ammoni a PSD in our study, defined as two times the standard de viation of the blank values, was 0.18 ug m

− 3 for 3 week integrated deployments, which compares favorably with prev ious passive ammonia field studies. 13,14,20 Every deployment involved duplicate sampling for both field sample s and field transport blanks. The two field transport blanks were averaged and subtracted from each field sample. The two field samples were then averaged for the final ammonia concentration. All calculati ons were done in accordance withthe Ogawa sampling protocol for ammonia 21 and included corrections fo r local ambient temperature. Since 2004 the Cherokee Nation has operated a c ontinuous ammonia monitor at their Stilwell, Oklahoma site. The continuous ammonia monitor is a Pranalytica Nitrolux 200 continuous trace level ammonia analyser, which measures ambient ammonia concentrations by ultrasonic acoustic spectroscopy. Weekly performance checks ( e.g. for error or maintenance flags, filt er or battery change, laser overheat) on the Nitrolux instrument are conducted by the Cherokee Na tion, and once every year th e instrument is sent to Pranalytica for checkout and any required repairs. For 2007 the St ilwell Nitrolux instrument was operated from January 1 through September 15, 2007. 2.3 Laboratory procedures 2.3.1 Sample preparation and handling. Since gaseous ammonia is ubiqui tous in trace quantities in the laboratory environment ( e.g. from human breath and in moisture from sweat glands), and since it was desired to credibly monitor low regional background ammonia concentrations, great care was taken in preparing and handling the passive ammonia PSDs. First, the ammoni a PSDs were prepared in an ammonia-scrubbed down-draft clean hood. The PSDs were then placed into thick (at least 0.05 millimetres thick) Ziploc bags, and the Ziploc bags were then placed into SC475 68 millilitre (ml) pl astic vials with tight screw caps (from Environmenta l Express in Mt. Pleasant, South Ca rolina). The plastic vials, along with log sheets and return mail labels, were then pa cked into thermal bags for either FedEx or UPS small box shipping. Onsite sample change-out training was conducted wi th all of the operators for all of the sites for consistency and to further help in minimizing sample contamination. Powder-free disposable gloves were employed by all laboratory chem ists and monitoring site operators. 2.3.2 Chemical analyses. After each three weeks of sampling the ammonia PSDs were shipped back to the EPA Region 6 Houston laboratory. The ammoni a filters were removed from the PSDs under the down-draft clean hood. The filters were then extracted with 8 ml of deionized water and ultrasonicated for 45 minutes. Sample solutions were analysed using a Metrohm MIC-2 advanced modular ion chromatograph (IC). The Metrohm IC was equipped with a guard co lumn and MetroSep C2-250 (4 millimetres (mm) by 250 mm) separation column for cat ions. An eluent mixture of 4 millimoles (mM) tartaric acid plus 1 mM 2,6-pyridine dicarboxyl ic acid (PDCA) at a fl ow rate of 1 ml min

− 1 was used to elute the ammonium ion (IC detect ion limit for the ammonium ion = 0.025 ppm). The IC was used in nonsuppressed conductivity detect ion mode with detector settings at a range of one millisiemen per centimetre (mS cm

− 1 ) and 100 uS cm

− 1 full scale. 

### 3. Results and discussion 3.1 Precision and comparisons of the passive data The precision for the year-long study wa s reviewed by analysis of the ab solute differences of 124 data pairs from all seven sites ( Fig. 2 ), using the median absolute differenc e and 90th percentile of all of the absolute difference values per Sirois and Vet. 22 The absolute difference betw een duplicate field samples Page 4 of 11 Baseline ambient gaseous ammonia concentrations in the Four Corners area and ea..... (DOI: 10.1

...

9/30/2008 htt p ://www.rsc.or g /delivery/

_

ArticleLinkin g /ArticleLinkin g .cfm?JournalCode=EM&Year=2008&

...had a median value of 0.1 ppb with 90% having a 0.3 ppb or lower difference. Lower precision was measured at the higher ambient ammoni a concentrations (all from the Qu apaw site). For the 16 data pairs from the Quapaw site the absolute difference betw een duplicate field samples had a median value of 0.2 ppb with 90% having a 0.75 ppb or lower difference.

The Ogawa PSDs used in this study have been successfully validated and used in previous published studies. 13,14,18 To support our confidence that the Ogawa PS Ds were providing reli able indicators of ambient ammonia concentrations, we conducted two da ta comparisons. First, at the Stilwell site, the passive ammonia data were compared to the conti nuously running Nitrolux m onitoring data. The Nitrolux monitor operated through September 15, 2007. As seen in Fig. 3 , the passive ammonia data overall tracked well with the Nitrolux ammonia data, with the Nitr olux ammonia concentrations usually higher than the passive ammonia concen trations. The correlation coefficient, r , was 0.74. The difference in arithmetic means was 0.7 ppb, but was not statistically signifi cant (2.6 ppb mean ammonia concentration for the Nitrolux versus a 1.9 ppb mean ammonia concentration for the passive samples). It is important to note that since the Nitrolux monito r was not calibrated on site ( i.e. only calibrated by the manufacturer once a year), the data from the Nitrolux monitor could only be viewed as providing an estimate of ambient ammonia concentrations rather than providing mo re precise measurements of ambient ammonia concentrations. Second, also at the Stilwell site, the passive ammonia data were compared to supplementary passive ammonia data being collected through a shor t-term Environment Canada study. Both studies used the Ogawa passive sampling devi ce (PSD), with the Envir onment Canada Ogawa PSDs slightly modified ( i.e. using 25 millimetre diameter filters instead of 14.5 milli metre diameter filters, and having more holes in the diffusion ba rriers), and operating at 2 week inte rvals instead of 3 week intervals. The Environment Canada PSDs were loaded, unloaded and analysed at their own laboratory in Toronto, Canada. The Environment Canada ammonia study ra n through March, 2007, so a three month comparison with the EPA Region 6 passive da ta was possible. As seen in Table 1 the six week and twelve week average concentrations of the EPA Region 6 passive ammonia data and the Envi ronment Canada passive ammonia data compared within +7% at best and within

− 20% at worst (calculated as 100× [EPAEC]/EPA). Table 1 Comparison of EPA Region 6 and Environment Canada Ogawa passiv e sample data at the Stilwell site; mean ammonia concentrations; 2007 Fig. 2 Precision of the Ogawa NH 3 PSDs for the 2007 Four Corners area and eastern Oklahoma passive ammonia study.

Time period EPA Region 6 sampler mean (ppb) Environment Canada sampler mean (ppb) 1/2–2/13 (first 6 weeks) 1.5 1.4 2/13–3/27 (second 6 weeks) 2.0 2.4 Page 5 of 11 Baseline ambient gaseous ammonia concentrations in the Four Corners area and ea..... (DOI: 10.1

...

9/30/2008 htt p ://www.rsc.or g /delivery/

_

ArticleLinkin g /ArticleLinkin g .cfm?JournalCode=EM&Year=2008&

...Additional information which contri buted to confidence in the passi ve data was obtained from the Quapaw Tribe source-oriented site. This site not only prov ided important data for the tribe concerning ambient ammonia concentrations close to a local mushroom proc essing facility ( i.e. about 0.75 miles NNE of the facility), but also checked the ability of the PSD to adequatelyrecord higher concentrations of ambient ammonia concentrations compared to the c onsiderably lower ambient ammonia concentrations recorded at the Four Corner s area and Stilwell sites. Fig. 4 shows the time series of all passive ammonia samples taken at the Quapaw site (first samples taken July 13–July 31, 2007). The first four sampling periods involved collocated samples taken at slightly different heights (3 metres agl versus 5 metres agl), and those samples tracked close with the platform ambient ammonia concentrat ion average at 4.9 ppb and the trailer top ambient ammonia concentration aver age at 5.0 ppb. For the second four sampling periods, the trailer top pair of duplicate samples was moved about 0.25 miles closer to the mushroom processing plant. All samples tracked well with the samples clos er to the mushroom proce ssing facility recording the higher passive ammonia concen trations (6.4 ppb average at 0.5 miles from the facility versus a 4.8 ppb average at 0.75 miles from the facility). 1/2–3/27 (entire 12 weeks) 1.7 1.9

Fig. 3 Comparison of 3 week integrated passive ammonia data with continuous hourly Nitrolux ammonia data at the Stil well, Oklahoma site; data capture of the Nitrolux monitor > 70% for each time period; 12/12/06–9/11/07. Page 6 of 11 Baseline ambient gaseous ammonia concentrations in the Four Corners area and ea..... (DOI: 10.1

...

9/30/2008 htt p ://www.rsc.or g /delivery/

_

ArticleLinkin g /ArticleLinkin g .cfm?JournalCode=EM&Year=2008&

...3.2 Time series analyses A time series of the 3 week integr ated passive ammonia samples was constructed for each site for the yearlong 2007 study period. For the five Four Corners area sites ( Fig. 5 ) the time series traces of passive ammonia concentrations generally increased from the beginning winter months to the warmer summer months, reaching peak ammonia concentrations during the July 10–July 31, 2007 time period, before generally decreasing in concentrati ons during the fall months. There were two notable exceptions to this general trend. First, the S outhern Ute site recorded an additiona l peak ammonia concentration during the spring (the April 17–May 8, 2007 time period). There is moderate local agricultural activity around the Southern Ute site, so field fert ilization probably caused the spring peak. Second, the Substation site, impacted by two coal-fired power plants, recorded additional peak ammonia concentrations during the fall (the October 2–October 23, 2007 and the October 23 –November 13, 2007 time periods). These fall concentrations at the Substation site were also the highest ambient ammonia concentrations recorded in the Four Corners area for the year-long study.

The time series trace for the Stil well, Oklahoma site is shown in Fig. 6 . The Stilwell site recorded its peak ambient ammonia concentration during the spring (the March 27–April 17, 2007 time period), probably due to agricultur al fertilization activity. Table 2 displays the summary statistics for the five Four Corners area sites and the Stilwell, Oklahoma site. Of note is that the Stilwell site, representin g re g ional Fig. 4 Passive ammonia data time series for the Quapaw, Oklahoma site; 3 w eek integrated samples.

Fig. 5 Passive ammonia data time series for the Four Corners area sites; 3 week integrated samples; ending dates 1/3/08 for Southern Ute and 1/22/08 for Mesa Verde NP. Page 7 of 11 Baseline ambient gaseous ammonia concentrations in the Four Corners area and ea..... (DOI: 10.1

...

9/30/2008 htt p ://www.rsc.or g /delivery/

_

ArticleLinkin g /ArticleLinkin g .cfm?JournalCode=EM&Year=2008&

...b ackground ammonia concentrations fo r eastern Oklahoma (1.8 ppb arithm etic mean), was nine times higher than the regional background site for the Four Corners area (0.2 ppb arithmetic mean at Mesa Verde National Park). Agricultural amm onia emissions, including microbial d ecomposition of animal waste from confined animal feeding operations (CAFOs), are hi gher in the region around eastern Oklahoma compared to the Four Corners area, resulting in a greater c ounty ammonia emissions density for the Stilwell site versus the Four Corners area. 23 Table 2 Summary statistics for Four Corners area and St ilwell, Oklahoma passive ammonia sites; 3 week integrated samples; December 12, 2006–December 26, 2007 a

In the Four Corners area, the urban Farmington Air port site recorded the hi ghest annual mean ammonia concentration (1.5 ppb), followed by the power plant imp acted Substation site (1.1 ppb). The rural Navajo Lake site, located in an area with growing oil and gas production, recorded an annual mean ammonia concentration (0.2 ppb) identical to the regional backgr ound site at Mesa Verde National Park. The Southern Ute site, also located in an area with growing oil and gas producti on but with added mobile source impacts, recorded a hi g her annual mean of 0.8 ppb. Site (type) Mean (ppb) Min. (ppb) Max. (ppb) (ppb) 95% confidence interval around mean (ppb) Substation (power plant impacted) 1.1 0.2 3.5 0.9 0.7–1.6 Farmington Airport (urban) 1.5 0.5 2.9 0.5 1.2–1.7 Navajo Lake (rural, oil/gas impacted) 0.2 No detection 0.5 0.1 0.1–0.3 Southern Ute (oil/gas/mobile source impacted) 0.8 0.3 1.5 0.3 0.7–1.0 Mesa Verde NP (rural, regional background) 0.2 No detection 0.6 0.2 0.1–0.3 Stilwell (rural, regional background) 1.8 0.8 3.3 0.6 1.5–2.1

a Ending dates December 31, 2007 for Substation, Farmington Airport and Navajo Lake, Janua ry 3, 2008 for Southern Ute, and January 22, 2008 for Mesa Verde NP.

Fig. 6 Passive ammonia data time series for the Stilwell, Oklahoma site; 3 week integrated samples. Page 8 of 11 Baseline ambient gaseous ammonia concentrations in the Four Corners area and ea..... (DOI: 10.1

...

9/30/2008 htt p ://www.rsc.or g /delivery/

_

ArticleLinkin g /ArticleLinkin g .cfm?JournalCode=EM&Year=2008&

...3.3 Examination of the passive data in a national and international context
The Four Corners area and eastern Ok lahoma passive ammonia data were re viewed in the context of other United States and Internati onal ammonia monitoring studies. Table 3 presents summaries of some yearlong ambient ammonia monitori ng studies culled from a current litera ture review. The Four Corners area and eastern Oklahoma ranges of annual mean concentr ations for ambient ammonia are lower compared to the International and Delaware, U. S. studies, but similar to the c oncentration ranges seen in the southeastern U.S. states. Peak ambi ent ammonia concentrations in the sp ring or summer or fall were seen at sites in all of the studies, withwinter maxima occurrences rare. Table 3 Comparison of Four Corners area and eastern Oklahoma passive ammonia data with other USA and International studies



### 4. Conclusion The 2007 passive ammonia monitoring study in the Four Corners area and eastern Oklahoma was important because it provided first ti me year-long baseline data of ambi ent ammonia concentrations in the Four Corners area and eastern Oklahoma in a simple and cost-effective manner, and it added new multisite ambient ammonia concentration in formation for additional areas in th e United States. It is important for air quality managers, when assessing nitrogen oxide emission controls for ambient ozone mitigation, to also consider ambient ammonia and at mospheric visibility impacts. The pa ssive ammonia data in this study had a median absolute difference between duplicate field samples of 0.1 ppb, and compared favorably to other collocated passive data and a collocated continuous instrument at the Stilwell, Oklahoma site. In a larger context, the Four Corners area/eastern Oklahoma 2007 ambient am monia concentrations were lower compared to previous international and eastern U.S. st udies, but similar to previ ous measurements taken in some southeastern U.S States. In the future, after the implementation of new nitrogen oxide controls on oil/ g as and power plant sources in the Four Corners area alon g with an y g rowth in other ammonia sources, Study area (reference #) Time period Range of annual mean concentrations (ppb) Peak season(s) Four Corners Area, USA, New Mexico, Colorado (this study) 12/2006–1/2008 0.2–1.5 Summer and fall (also one spring peak) Eastern Oklahoma, USA (this study) 12/2006–12/2007 1.8 (one site) Spring Delaware inland bays, USA 14 4/2000–4/2001 <0.7–>8.6 Spring and summer SE USA, Georgia, Alabama, Mississippi, Florida 17 1/2004–12/2004 0.23–2.44 Spring and late summer/fall Denmark heathland 24 5/1995–5/1996 2.9 (one site) Spring Scotland, UK 10 m from road edges 25 4/2002–4/2003 0.2–4.5 Rural, semi-rural: late summer/fall Other sites with high background: winter Austria and Bavaria 5 10/1995–10/1996 and 4/1998–4/1999 1.3–9 Rural: summer 36 regional sites in Asia, Africa and South America 7 9/1999–8/2000 <1–22 (median values ) Site to site variations
Netherlands 8 9/2000–9/2001 1.4–25.7 Spring Switzerland 9 10/1999–9/2000 0.6–10.7 Summer Page 9 of 11 Baseline ambient gaseous ammonia concentrations in the Four Corners area and ea..... (DOI: 10.1

...

9/30/2008 htt p ://www.rsc.or g /delivery/

_

ArticleLinkin g /ArticleLinkin g .cfm?JournalCode=EM&Year=2008&

...multiple passive samplers are planned to be deployed again to determine if ambient ammonia concentrations have significantly changed from the 2007 baseline data. Si milarly in eastern Oklahoma in the future, passive samplers could be deployed again to determine if ammonia co ncentrations, largely from regional agricultural emissions, have significantly changed. It is reco mmended that the future studies be multi-year in duration in order to properly assess inter-annual vari ability of the ambient ammonia concentrations. The 2007 (and future) passive ammonia da ta should prove useful to modelers in present and future atmospheric visibility modeling exercises of both the Four Corners area and eastern Oklahoma. The models should be more accurate with inclusion of the passive am bient ammonia data, and the models will help determine if any atmospheric changes in ammonia concentrations signifi cantly affect atmospheric visibility. 

### Acknowledgements The authors are grateful to all the field operators involved in day to day careful ambient data collection. The authors thank Mr. Till Stoeckenius of ENVIRON Co rporation for review of the draft manuscript, and thank Maria Martinez, David Nelei gh, Rick McMillin and Dr Melvin Ritter for their support of passive monitoring studies. The authors also thank Melody Lister and Jeff Da nielson for the excellent GIS map production. 

### References

1 Four Corners Air Quality Task Force, Four Corners Air Quality Task Force Report of Mitigation Options , November 1, 2007, http://www.nmenv.state.nm .us/aqb/4C/DraftTaskForceReport.html, accessed May 7, 2008. 2 The U.S. Environmental Protection Agency, Nationa l Ambient Air Quality Standards for Ozone; Final Rule, Fed. Regist. , 2008, 73 (60), 16436–16514. 3 S. Mukhtar, A. Mutlu, S. C. Capareda and C. B. Parnell, Seasonal and Spatial Variations of Ammonia Emissions from an Open-Lot Dairy Operation, J. Air Waste Manage. Assoc. , 2008, 58 , 369–376 [Links]

. 4 K. J. Olszyna, S. T. Bairai and R. L. Tanner, Effect of ambient NH 3 levels on PM2.5 composition in the Great Smoky Mountains National Park, Atmos. Environ. , 2005, 39 , 4593–4606 [Links]

. 5 M. Loflund, A. Kasper-Giebl, S. Stopper, H. Urban, P. Biebl, M. Kirchner, S. Braeutigam and H. Puxbaum, Monitoring ammonia in urban, inne r alpine and pre-alpine ambient air, J. Environ. Monit. , 2002, 4 , 205–209 [Links]

. 6 A. Spangenberg, F. Hofmann and M. Kirchner, De termining the agricultur al ammonia immission using bark bio-monitoring: comparison with passive sampler measurements, J. Environ. Monit. , 2002, 4 , 865–869 [Links]

. 7 G. R. Carmichael, M. Ferm, N. Thongboonchoo, J.-H. Woo, L. Y. Ch an, K. Murano, P. H. Viet, C. Mossberg, R. Bala, J. Boonjawat, P. Upatum, M. Mohan, S. P. Adhikary, A. B. Shrestha, J. J. Pienaar, E. B. Brunke, T. Chen, T. Jie, D. Guoan, L. C. Peng, S. Dhiharto, H. Harjanto, A. M. Jose, W. Kimani, A. Kirouane, J.-P. Lacaux, S. Richard, O. Barturen, J. C. Cerda, A. Athayde, T. Tavares, J. S. Cotrina and E. Bilici, Measurements of sulfur di oxide, ozone and ammonia concentrations in Asia, Africa, and South America using passive samplers, Atmos. Environ. , 2003, 37 , 1293–1308 [Links]

. 8 A. van Pul, H. V. Jaarsveld, T. van der Meulen and G. Velders, Ammonia concentrations in the Netherlands: spatially detailed meas urements and model calculations, Atmos. Environ. , 2004, 38 , 4045–4055 [Links]

. 9 L. Thoni, P. Brang, S. Braun, E. Seitler and B. Rihm, Ammonia monitori ng in Switzerland with passive samplers: patterns, determinants an d comparison with modelled concentrations, Environ. Monit. Assess. , 2004, 98 , 93–107 [Links]

. 10 T. Cassel, L. Ashbaugh, R. Flocchini and D. Meyer, Ammonia Flux from Open-Lot Dairies: Development of Measurement Me thodology and Emission Factors, J. Air Waste Manage. Assoc. , Page 10 of 11 Baseline ambient gaseous ammonia concentrations in the Four Corners area and ea..... (DOI: 1

...

9/30/2008 htt p ://www.rsc.or g /delivery/

_

ArticleLinkin g /ArticleLinkin g .cfm?JournalCode=EM&Year=2008&

...2005, 55 , 816–825 [Links]

. 11 T. Cassel, L. Ashbaugh, R. Flocchini and D. Meyer, Ammonia Emission Factors for Open-Lot Dairies: Direct Measurements and Estimation by Nitrogen Intake, J. Air Waste Manage. Assoc. , 2005, 55 , 826–833 [Links]

. 12 L. Frati, S. Santoni, V. Nicolardi, C. Gaggi, G. Brunialti, A. Guttova, S. Gaudino, A. Pati, S. A. Pirintsos and S. Loppi, Lichen biomonitoring of ammonia emission and nitr ogen deposition around a pig stockfarm, Environ. Pollut. , 2007, 146 , 311–316 [Links]

. 13 M. J. Roadman, J. R. Scudlark, J. J. Meisinge r and W. J. Ullman, Validation of Ogawa passive samplers for the determination of gaseous amm onia concentrations in agricultural settings, Atmos. Environ. , 2003, 37 , 2317–2325 [Links]

. 14 J. R. Scudlark, J. A. Jennings, M. J. Roadman, K. B. Savidge and W. J. Ullman, Atmospheric nitrogen inputs to the Delaware Inland Bays: the role of ammonia, Environ. Pollut. , 2005, 135 , 433–443 [Links]

. 15 S. M. Wilson and M. L. Serre, Use of passive samplers to measure atmosphe ric ammonia levels in a high-density industrial hog farm area of eastern North Carolina, Atmos. Environ. , 2007, 41 , 6074– 6086 [Links]

. 16 V. P. Aneja, A. B. Murthy, W. Battye, R. Battye and W. G. Benjey, Analysis of Ammonia and Aerosol Concentrations and Deposition near th e Free Troposphere at Mt. Mitchell, NC, USA, Atmos. Environ. , 1998, 32 , 353–358 [Links]

. 17 E. S. Edgerton, R. D. Saylor, B. E. Hartsell, J. J. Jansen and D. A. Hans en, Ammonia and ammonium measurements from the s outheastern United States, Atmos. Environ. , 2007, 41 , 3339–3351 [Links]

. 18 M. E. Fenn, L. Geiser, R. Bachman, T. J. Bl ubaugh and A. Bytnerowicz, Atmospheric deposition inputs and effects on lichen chemis try and indicator species in the Columbia River Gorge, USA, Environ. Pollut. , 2007, 146 , 77–91 [Links]

. 19 C. Hunsaker, A. Bytnerowicz, J. Auman and R. Cisneros, Air Pollution and Watershed Research in the Central Sierra Nevada of California: Nitrogen and Ozone, Sci. World J. , 2007, 7 (S1), 206–221. 20 L. Thoni, E. Seitler, A. Blatter and A. Neftel, A passive sampling method to determine ammonia in ambient air, J. Environ. Monit. , 2003, 5 , 96–99 [Links]

. 21 NH 3 Sampling Protocol Using the Ogawa Sampler , version 3.98, Yokohama CityResearch Institute for Environmental Science, Yokohama, Japan, 1st edn, September 2005. 22 A. Sirois and R. Vet, The Precision of Precipitati on Chemistry Measurements in the Canadian Air and Precipitation Monitori ng Network (CAPMON), Environ. Monit. Assess. , 1999, 57 , 301–329 [Links]

. 23 U.S. EPA Air Data , Ammonia emissions density (tons/square mile) data , www.epa.gov/air/da ta/geosel.html, accessed on May 8, 2008. 24 B. Hansen, Weekly Measurements Over One Year of Ammonia Con centrations and Surface Exchange Fluxes at a Danish Heathland wi th Passive Wind-Vane Flux Sample rs in an Aerodynamic Gradient Configuration, Water, Air, Soil Pollut. , 1999, 113 , 357–370 [Links]

. 25 J. N. Cape, Y. S. Tang, N. van Dijk, L. Love, M. A. Sutton and S. C. F. Palmer, Concentrations of ammonia and nitrogen dioxide at roadside verges , and their contribution to nitrogen deposition, Environ. Pollut. , 2004, 132 , 469–478 [Links]

. This journal is © The Royal Society of Chemistry 2008 Page 11 of 11 Baseline ambient gaseous ammonia concentrations in the Four Corners area and ea..... (DOI: 1

...

9/30/2008 htt p ://www.rsc.or g /delivery/

_

ArticleLinkin g /ArticleLinkin g .cfm?JournalCode=EM&Year=2008&

...