1 

## A Pilot Monitoring Study of Atmospheric NHx at Selected

IMPROVE sites

Extended Abstract # 19

Xi Chen 1 , Derek Day 2 , Bret Schichtel 2 , William Malm 2 , Jose Mojica 3 , Chuck McDade 3

, Eva

Hardison 4

, Sonia M. Kreidenweis 1 , and Jeffrey L. Collett, Jr. 1 ,*

1 Atmospheric Science Department, Colorado State University, Fort Collins, CO 80523 USA

2 NPS/CIRA, Colorado State University, Fort Collins, CO 80523 USA

3 Crocker Nuclear Laboratory, University of California, Davis, CA 95616 USA

4

* Corresponding author. Tel.: +1970 491 8697; fax: +1970 491 8483

.

Environmental Chemistry Department, RTI International, RTP, NC 27709 USA

E

- mail address: collett@atmos .colostate.edu (J.L. Collett Jr).



### INTRODUCTION

Among all reactive nitrogen

- bearing species, a mmonia (NH 3 ) is the most abundant basic gas in the atmosphere. The primary sources for atmospheric NH 3 are agricultural emissions such as domestic animals, nitrogen fertilizer application and biomass burning

. 1,2 Due to its acid neutralizing capacity, NH 3 can react with acidic species (e.g., H 2 SO 4 , HNO 3 and HCl) to form secondary inorganic particles.

Visibility is one of most desirable elements in Class I areas like national parks. T he Interagency Monitoring of Protected Visual Environments (IMPROVE) program has been measuring visibility degrading aerosols since 1988 in federally protected areas

. 3,4 Most IMPROVE sites have particle measurements of PM 2.5 mass, elements by XRF, ne gative ions and EC/OC, but no direct cation monitori ng

. 3 Despite the importance of gaseous ammonia in forming atmospheric aerosols and contributing to nitrogen deposition and visibility degradation

, ammonia /ammonium is rarely regularly measured by existing air quality monitoring networks.

The o bjective of this study is in validating whether IMPROVE samplers could be modified to incorporate acid

- impregnated filters to monitor ammonia/ammonium with acceptable accuracy and precision , which is eventually adopted to address ammonia partitioning between ga s and particle phase, monitor impacts from particle formed from ammonia

neutralization on visibility in national parks, and determine sources and contributions of ammonia to excess nitrogen deposition in Rocky Mountain ecosy stems.



### EXPERIMENTAL DESCRIPTIONS

Samplers for NHx (NH 3 and NH 4 + ) study were adapted from regular IMPROVE sampler module B which is installed for monitoring anion species by nylon filters. The IMPROVE mod ule B sampler was originally coupled wit h a carbonate

- coated denuder to remove nitric acid as the nylon filters used for IMPROVE particle collection tend to retain gaseous acidic species, 5
but since the purpose of this study is to measure ammonia/ammonium, the nitric acid denuder is

not included in the modified version

. 3 7mm cellulose fiber filters coated with phosphorous acid2 ( 225

- 18A , SKC Inc., Eight Four, PA ) were used for sampling NHx

. The acid

- coated cellulose
filters used are designed to collect both gas phase NH 3 and PM 2.5 particle phase N H 4 + ; NHx is adopted to refer to a collective of collected NH 3 and N H 4 +

Acid coated cellulose filters were loaded in or unloaded from sampler cartridges in a laminar flow hood or a nitrogen

- atmosphere rigid glovebox with ammonia scrubbing to ensure low background influence to accurately interpret the obtained sampling results. Both sampled cellulose and nylon filters were extracted for ammonium concentration measurements. Collected
filters were extracted in DI wa ter using sonicator for 45 min. Ammonia/ammonium

concentrations were ana lyzed using ion chromatography with Dionex CS12A separation column

. .

Through a pilot study initiated in June 2010, total NHx is being measured on a 1

- in

- 3 day sampling basis at 9 IMPROVE sites, mostly in the Rocky Mountain region of the western U.S.
Table 1 lists details of site locations and elevations., IMPROVE NHx cartridges for each week were kept in individual zip

- seal bag s with a pieces of phosphorous acid

- soaked paper towel included in shipping/storage as NH 3

Table 1. IMPROVE NHx sampling site locations and estimated NH scrubber. Sample cartridge assembly and sample loadings were completed at Colorado State University (CSU) and cartridges were shipped directly to site
operators; while collected sample filters were returned to Research Triangle Institute (RTI) for unloading and subsequent analysis.

3 /NH 4 +

Site dry deposition fluxes.

Site code Latitude Longitude Elev atio n (m) NH 3 Dep (k

gN/ha/yr) dry NH 4 + Dep (k

gN/ha/yr) dry

Bandelier, NM BANDS 35.7797

- 106.2664 1988

Bondville, IL BONDS 40.0520

- 88.3733 263 1.72±0.75 0.21±0.07

Cedar Bluff, KS CEBLS 38.7701

- 99.7634 665

Chiricahua, AZ CHIRS 32.0094

- 109.3890 1554 0.42±0.46 0.17±0.10

Glacier, MT GLACS 48.5105

- 113.9966 975 0.27±0.21 0.01±0.01

Mesa Verde, CO MEVES 37.1984

- 108.4907 2172 0.09±0.09 0.09±0.04
Rocky Mountain, CO ROMOS 40.2783

- 105.5457 2760 0.16±0.15 0.08±0.02

Wind Cave, SD WICAS 43.5576

- 103.4838 1296 0.23±0.19 0.11±0.02

Yellowstone, WY YELLS 44.5653

- 110.4002 2425 0.09±0.03 0.05±0.00



### RESULTS AND DISCUSSION
Collocated sampling t ests at CSU for two weeks revealed excellent agreement between
total NHx measurements made using the NHx IMPROVE module and a conventional URG
annular denuder/filter

- pack sample, meaning that the adapted IMPROVE sampling modules provide reliable measurements at a much lower cost, which are significant concerns and improvements for monitoring of atmospheric pollutants

.
After NHx sampling began in June 2010, a n unidentified prominent peak was observed to
elute after the ammonium peak in IC analysis . The mysterious peak was subsequently determined as methylamine after co mparing with standards and independent validat ion by t ime

of

- flight mass spectrometry. T he source of the appearance of methylamine was successfully

assessed and identified

, which was discovered to be a chemical artifact associated with reaction3 of collecte d ammonia/ammonium on filters wi th the sampling holder in use. The material used
for the filter holder was Polyoxymethylene (POM), which was susceptible to acid degradation.

These findings led to uncovering an unforeseen incompatibility of the material used for standard deployment of IMPROVE network filters with the acid

- coated filters for ammonia/ammonium

collection. Acid etching of IMPROVE POM cartridges was reflected as degradation in releasing formaldehyde. Methylamine as a chemical artifact in this case was subsequently formed from released formaldehyde and collected ammonia/ammonium on filters. Temperatures, duration of

filter stora ge inside cartridges, and degree of acid etching on POM cartridges appear ed to determine extent of methylamine formation and NH 4 +

NHx field blanks collected from April 2011 to January 2012 did not suggest much difference from site to site with average concentration of 0.030±0.007 μg/m loss. After further compatibility tests, Polypropylene was proven to successfully meet all aspects required for NHx sampling ; new cartridges were manufactured and IMPROVE NHx sampling resumed starting from late April

2011.

3

Dry deposition of NH . Collocated samplers were installed at Rocky Mountain National Par k ( ROMOS ) and Bondville, IL ( BONDS ) . Precision of collected NHx suggest that collocated samplers yield excellent
agreement. Monthly average concentrations for IMPROVE NHx sites from April to January 2012 are shown in Figure 1. Overall NHx observed for the sample period at YELLS was lowest in concentration, while CEBLS and BONDS were the highest. NHx measurements showed a pattern of increasing NHx concentrations in late spring/early summer (June) and a decrease in winter, starting in September for most of th e sites. This pattern is consistent with expected seasonal patterns in emissions of ammonia. Both BONDS and CEBLS, however, still exhibit quite abundant winter NHx, which may reflect continued agricultural emissions trapped within a
shallower winter bound ary layer.

3 /NH 4 + was estimated by adopting SO 2 /particulate dry deposition velocities calculated by the Multi

- Layer Model used by CASTNET, which had sites co

- located with most of the pilot IMPROVE NHx samplers (except sites BANDS and CEBLS). As
CAS T NET only reports dry deposition velocities for SO 2 , HNO 3 and fine particles, estimation s of NH 3 deposition velocities were estimated based on those of SO 2 and a scaling factor. Given that solubility is the dominant contributor to determine deposition velocities, SO 2 and NH 3 , with similar solubility as reflected in Henry’s or effective Henry’s law coefficient, are most likely to track each other as of depos ition velocities under various conditions such as surface wetness. A ratio of deposition velocities of NH 3 /SO 2 was estimated from model ing b y Zhang et al. 6 under various land use types and wetness to be 1.15±0.14. Dry deposition fluxes were determined
from NH 3 /NH 4 + concentrations along with dry deposition velocities on a monthly basis . A verage fluxes determined from 04/2011 to 11/2011 are tabulated in table 1. NH 4 + c oncentrations derived in this study

, from cation analysis of the regular IMPROVE ion module filter, r epresent a lower
bound on true values due to volatilization loss of NH 4 + from nylon filters

. Since NH 3 is obtained

as ( NH
x – NH 4 + ) , estimated NH 3 concentrations should be considered upper bounds to the true
values. Because of its much higher deposition veloci t y , dry NH 3 is observed to be a much larger contributor to reactive nitrogen deposition than dry NH 4 + throughout the study region . Dry

NH 3 /NH 4 + deposition flux at BONDS is observed much higher than other sites and possibly exceeding critical loads fo r nitrogen deposition, whi ch was estimated at around 1.5 k gN/ha/yr of nitrogen wet deposition. 7, 84 Figure 1. IMPROVE NHx concentrations from April 2011 to January 2012.



### SUMMARY

IMPROVE samplers were adapted to collect total NHx (gas phase ammonia and particle phase ammonium) to monitor particle impact s on visibility, and determine sources and contributions of ammonia to excess nitrogen deposition in Rocky Mountain ecosystems. Selected sampling site include 9 IMPROVE sites: Rocky Mountain, CO; Mesa Verde , CO; Yellowstone, WY; Glacier, MT; Bandelier, NM; Bondville, IL ; Cedar Bluff, KS ; Wind Cave, S D ; Chiricahua,

AZ . Phosphorous acid coated cellulose filters were evaluated to det ermine their ability to accurately monitor total NHx. Tests in Fort Collins, CO revealed excellent agreement between

total NHx measurements made using the new IMPROVE module and a conventional URG
annular denuder/filter

- pack sample . The IMPROVE NHx sampli ng module can provide reliable

measurements of total NHx at a much lower cost than conventional, multi

- component samplers, facilitating its widespread deployment. Initial NHx filter cartridges were machined from Polyoxymethylene (POM), which proved suscept ible to acid degradation and resulted in artifact methylamine formation during field deployment in 2010. Methylamine was formed from released formaldehyde and collected ammonia/ammonium on filters. After further testing, the

filter holders were remanufactu red from p olypropylene . This eliminated the artifact amine formation and the pilot network was restarted in spring 2011 with the new design. NHx measurements conducted from April to December 2011 showed a pattern of increasing NHx

concentrations in late s pring/early summer (June) and a decrease in winter, starting in September5 for most of the sites. This pattern is consistent with expected seasonal patterns in agricultural
emissions of ammonia. Both Bondville and Cedar Bluff , however, still exhibit quite abundant winter NHx, which may reflect continued agricultural emissions trapped within a shallower winter boundary layer. Dry deposition of NH 3 /NH 4 + was estimated by adopting SO 2



### ACKNO W LEDGMENTS /particulate dry deposition velocities calculated by the Multi

- Layer Mode l us ed by CASTNET, which had
sites co

- located with most of the pilot IMPROVE NHx samplers.

This work was sponsored by the National Park Service through a cooperative agreement with Colorado State University (Task #J2350093004).



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