@article{yu_luo_pryor_pillai_lee_ortega_schwab_hallar_leaitch_aneja_et al._2015, title={Spring and summer contrast in new particle formation over nine forest areas in North America}, volume={15}, ISSN={["1680-7324"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84946816099&partnerID=MN8TOARS}, DOI={10.5194/acp-15-13993-2015}, abstractNote={Abstract. Recent laboratory chamber studies indicate a significant role for highly oxidized low-volatility organics in new particle formation (NPF), but the actual role of these highly oxidized low-volatility organics in atmospheric NPF remains uncertain. Here, particle size distributions (PSDs) measured in nine forest areas in North America are used to characterize the occurrence and intensity of NPF and to evaluate model simulations using an empirical formulation in which formation rate is a function of the concentrations of sulfuric acid and low-volatility organics from alpha-pinene oxidation (Nucl-Org), and using an ion-mediated nucleation mechanism (excluding organics) (Nucl-IMN). On average, NPF occurred on ~ 70 % of days during March for the four forest sites with springtime PSD measurements, while NPF occurred on only ~ 10 % of days in July for all nine forest sites. Both Nucl-Org and Nucl-IMN schemes capture the observed high frequency of NPF in spring, but the Nucl-Org scheme significantly overpredicts while the Nucl-IMN scheme slightly underpredicts NPF and particle number concentrations in summer. Statistical analyses of observed and simulated ultrafine particle number concentrations and frequency of NPF events indicate that the scheme without organics agrees better overall with observations. The two schemes predict quite different nucleation rates (including their spatial patterns), concentrations of cloud condensation nuclei, and aerosol first indirect radiative forcing in North America, highlighting the need to reduce NPF uncertainties in regional and global earth system models.
                    }, number={24}, journal={ATMOSPHERIC CHEMISTRY AND PHYSICS}, author={Yu, F. and Luo, G. and Pryor, S. C. and Pillai, P. R. and Lee, S. H. and Ortega, J. and Schwab, J. J. and Hallar, A. G. and Leaitch, W. R. and Aneja, V. P. and et al.}, year={2015}, pages={13993–14003} }
 @article{pillai_walker_khlystov_aneja_2013, title={Formation and Growth of Atmospheric Particles at a Forest Site in the Southeast US}, volume={1527}, ISSN={["0094-243X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84877358779&partnerID=MN8TOARS}, DOI={10.1063/1.4803288}, abstractNote={Atmospheric particle size distribution measurements (10 ≤ aerodynamic diameter, Dp ≤ 250 nm), which took place above a loblolly pine plantation in the Southeast U.S. from November 2005 to September 2007, were made using Scanning Mobility Particle Sizer (SMPS). The size distributions were investigated to identify new particle formation and to classify the new particle formation episodes into different event classes based on the behavior of particle size distribution and particle growth pattern. About 69% of the observation days had nucleation. The event frequency was highest in spring and lowest in winter. The particle growth rate was highest in May (5.0 ± 3.6 nm hr−1) and lowest in February (1.2 ± 2.2 nm hr−1) with an annual average particle growth rate of 2.5 ± 0.3 nm hr−1. Nucleation frequency and event types are examined along with associated meteorological and chemical conditions.}, journal={NUCLEATION AND ATMOSPHERIC AEROSOLS}, author={Pillai, Priya and Walker, John and Khlystov, Andrey and Aneja, Viney}, year={2013}, pages={401–404} }
 @article{walker_spence_kimbrough_robarge_2008, title={Inferential model estimates of ammonia dry deposition in the vicinity of a swine production facility}, volume={42}, ISSN={["1873-2844"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-41449099938&partnerID=MN8TOARS}, DOI={10.1016/j.atmosenv.2007.06.004}, abstractNote={This project investigates NH3 dry deposition around a commercial swine production facility in eastern North Carolina. Passive diffusion-tube samplers were used to measure weekly integrated NH3 concentrations at 22 locations along horizontal gradients from the barn/lagoon emissions complex (source) out to a distance of 700 m. A two-layer canopy compensation point model was used to predict bi-directional NH3 exchange within a 500 m circular buffer surrounding the source. The model takes into account differences in soil and vegetation emission potential, as well as canopy physical characteristics, among three primary surfaces surrounding the site: forest, crops spray fertilized with swine waste, and other fertilized crops. Between June 2003 and July 2005, mean observed NH3 concentrations ranged from 169.0 μg NH3 m−3 at a distance of 10 m from the source to 7.1 and 13.0 μg NH3 m−3 at 612 and 698 m in the predominant upwind and downwind directions, respectively. Median predicted dry deposition rates ranged from 145 kg NH3–N ha−1 yr−1 at 10 m from the source to 16 kg NH3–N ha−1 yr−1 at 500 m, which is ≈3.5× wet deposition of NH4+–N. Assuming a steady-state emission factor of 7.0 kg NH3 animal−1 yr−1 and a median population of 4900 animals, NH3 dry deposition over the nearest 500 m from the barn/lagoon complex accounted for 10.4% (3567 kg NH3) of annual emissions (34,300 kg NH3). A model sensitivity analysis shows that predicted deposition rates are more sensitive to assumptions regarding cuticular uptake relative to soil and vegetation emission potentials.}, number={14}, journal={ATMOSPHERIC ENVIRONMENT}, author={Walker, John and Spence, Porche' and Kimbrough, Sue and Robarge, Wayne}, year={2008}, month={Apr}, pages={3407–3418} }
 @article{aneja_nelson_roelle_walker_battye_2003, title={Agricultural ammonia emissions and ammonium concentrations associated with aerosols and precipitation in the southeast United States}, volume={108}, ISSN={["2169-8996"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-1642562702&partnerID=MN8TOARS}, DOI={10.1029/2002jd002271}, abstractNote={Temporal and spatial variations in ammonia (NH3) emissions and ammonium (NH4+) concentrations associated with aerosols and volume‐weighted NH4+ concentration in precipitation are investigated over the period 1990–1998 in the southeast United States (Alabama, Florida, Georgia, Kentucky, North Carolina, South Carolina, Mississippi, and Tennessee). These variations were analyzed using an NH3 emissions inventory developed for the southeast United States and ambient NH4+ data from the various Clean Air Status and Trends Network (CASTNet) and the National Atmospheric Deposition Program/National Trends Network (NADP/NTN). Results show that natural log‐transformed annual NH4+ concentration associated with aerosols increases with natural log‐transformed annual NH3 emission density within the same county (R2 = 0.86, p < 0.0001, N = 12). Natural log‐transformed annual volume‐weighted average NH4+ concentration in precipitation shows only a very weak positive correlation with natural log‐transformed annual NH3 emission densities within the corresponding county (R2 = 0.12, p = 0.04, N = 29). Analysis of NH4+ concentration associated with aerosols at CASTNet sites revealed that temperature, precipitation amount, and relative humidity are the most statistically significant (p < 0.05) parameters in predicting the weekly concentrations of NH4+ during the period 1990–1998. Wind speed and wind direction were also statistically significant (p < 0.05) at several CASTNet sites, but the results were less consistent. Investigation into wet NH4+ concentration in precipitation consistently yielded temperature as a statistically significant (p < 0.05) parameter at individual sites. Trends over the period 1990–1998 revealed a slight decrease in NH4+ concentration at CASTNet site SPD, Claiborne County, Tennessee (2.14–1.88 μg m−3), while positive trends in NH4+ concentration in precipitation were evident at NADP sites NC35, Sampson County, North Carolina (0.2–0.48 mg L−1) and KY35, Rowan County, Kentucky (0.2–0.35 mg L−1) over the period 1990–1998.}, number={D4}, journal={JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES}, author={Aneja, VP and Nelson, DR and Roelle, PA and Walker, JT and Battye, W}, year={2003}, month={Feb} }
 @article{aneja_bunton_walker_malik_2001, title={Measurement and analysis of atmospheric ammonia emissions from anaerobic lagoons}, volume={35}, ISSN={["1873-2844"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0035126691&partnerID=MN8TOARS}, DOI={10.1016/S1352-2310(00)00547-1}, abstractNote={Ammonia-nitrogen flux (NH3-N=(14/17)NH3) was determined from six anaerobic swine waste storage and treatment lagoons (primary, secondary, and tertiary) using the dynamic chamber system. Measurements occurred during the fall of 1998 through the early spring of 1999, and each lagoon was examined for approximately one week. Analysis of flux variation was made with respect to lagoon surface water temperature (∼15 cm below the surface), lagoon water pH, total aqueous phase NHx(=NH3+NH4+) concentration, and total Kjeldahl nitrogen (TKN). Average lagoon temperatures (across all six lagoons) ranged from approximately 10.3 to 23.3°C. The pH ranged in value from 6.8 to 8.1. Aqueous NHx concentration ranged from 37 to 909 mg N l−1, and TKN varied from 87 to 950 mg N l−1. Fluxes were the largest at the primary lagoon in Kenansville, NC (March 1999) with an average value of 120.3 μg N m−2 min−1, and smallest at the tertiary lagoon in Rocky Mount, NC (November 1998) at 40.7 μg N m−2 min−1. Emission rates were found to be correlated with both surface lagoon water temperature and aqueous NHx concentration. The NH3-N flux may be modeled as ln(NH3-N flux)=1.0788+0.0406TL+0.0015([NHx]) (R2=0.74), where NH3-N flux is the ammonia flux from the lagoon surface in μg N m−2 min−1, TL is the lagoon surface water temperature in °C, and [NHx] is the total ammonia-nitrogen concentration in mg N l−1.}, number={11}, journal={ATMOSPHERIC ENVIRONMENT}, author={Aneja, VP and Bunton, B and Walker, JT and Malik, BP}, year={2001}, pages={1949–1958} }
 @book{aneja_chauhan_walker_2000, title={Atmospheric ammonia emissions from swine waste storage and treatment lagoons}, number={329}, journal={Report (Water Resources Research Institute of the University of North Carolina)}, publisher={Raleigh, NC: University of North Carolina Water Resources Research Institute}, author={Aneja, V. P. and Chauhan, J. P. and Walker, J.}, year={2000} }
 @article{walker_aneja_dickey_2000, title={Atmospheric transport and wet deposition of ammonium in North Carolina}, volume={34}, ISSN={["1873-2844"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0034114438&partnerID=MN8TOARS}, DOI={10.1016/S1352-2310(99)00499-9}, abstractNote={Wet deposition and transport analysis has been performed for ammonium (NH4+) in North Carolina, USA. Multiple regression analysis is employed to model the temporal trend and seasonality in monthly volume-weighted mean NH4+ concentrations in precipitation from 1983 to 1996 at six National Atmospheric Deposition Program/National Trends Network (NADP/NTN) sites. A significant (p<0.01) increasing trend beginning in 1990, which corresponds to an annual concentration increase of approximately 9.5%, is detected at the rural Sampson County site (NC35), which is located within a densely populated network of swine and poultry operations. This trend is positively correlated with increasing ammonia (NH3) emissions related to the vigorous growth of North Carolina's swine population since 1990, particularly in the state's Coastal Plain region. A source–receptor regression model, which utilizes weekly NH4+ concentrations in precipitation in conjunction with boundary layer air mass back trajectories, is developed to statistically test for the influence of a particular NH3 source region on NH4+ concentrations at surrounding NADP/NTN sites for the years 1995–1996. NH3 emissions from this source region, primarily evolving from swine and poultry operations, are found to increase NH4+ concentration in precipitation at sites up to ≈80 km away. At the Scotland County (NC36) and Wake County (NC41) sites, mean NH4+ concentrations show increases of at least 44% for weeks during which 25% or more back trajectories are influenced by this source region.}, number={20}, journal={ATMOSPHERIC ENVIRONMENT}, author={Walker, JT and Aneja, VP and Dickey, DA}, year={2000}, pages={3407–3418} }
 @article{aneja_chauhan_walker_2000, title={Characterization of atmospheric ammonia emissions from swine waste storage and treatment lagoons}, volume={105}, ISSN={["2169-8996"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0033784863&partnerID=MN8TOARS}, DOI={10.1029/2000jd900066}, abstractNote={Fluxes of atmospheric ammonia‐nitrogen (NH3‐N, where NH3‐N = (14/17)NH3) from an anaerobic ∼2.5 ha (1 ha = 10,000 m2) commercial hog waste storage lagoon were measured during the summer of 1997 through the spring of 1998 in order to study the seasonal variability in emissions of NH3‐N and its relationship to lagoon physicochemical properties. Ammonia‐nitrogen fluxes were measured during each season (summer, fall, winter, and spring) using a dynamic flow through chamber system. Measured lagoon physicochemical parameters included surface lagoon temperature (Tℓ°C, ∼15 cm below surface), lagoon pH, and Total Kjeldahl Nitrogen (TKN). The pH and TKN of the surface lagoon water ranged from 7 to 8 pH units, and 500 to 750 mg N L−1, respectively. The largest fluxes were observed during the summer (August 1997) (mean NH3‐N flux = 4017 ± 987 μg N m−2 min−1). Fluxes decreased through the fall (December 1997) months (844 ± 401 μg N m−2 min−1) to a minimum flux during the winter (February 1998) months (305 ± 154 μg N m−2 min−1). Emission rates increased during spring (May 1998) (1706 ± 552 μg N m−2 min−1), but did not reach the magnitude of fluxes observed during the summer. Lagoon emissions in eastern North Carolina were estimated to constitute ∼33% of total NH3‐N emissions from commercial hog operations in North Carolina based on current inventories for NH3‐N emissions published by the North Carolina Division of Air Quality, North Carolina Department of Environment and Natural Resources. The ammonia flux may be predicted by an observational model log10 (NH3‐N flux) = 0.048 Tℓ + 2.1.}, number={D9}, journal={JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES}, author={Aneja, VP and Chauhan, JP and Walker, JT}, year={2000}, month={May}, pages={11535–11545} }
 @article{walker_nelson_aneja_2000, title={Trends in ammonium concentration in precipitation and atmospheric ammonia emissions at a coastal plain site in North Carolina, USA}, volume={34}, ISSN={["0013-936X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0034284993&partnerID=MN8TOARS}, DOI={10.1021/es990921d}, abstractNote={The temporal characteristics of annual volume-weighted average ammonium (NH4+) ion concentration in precipitation and local ammonia (NH3) emissions are investigated over the period 1982−1997 at Nat...}, number={17}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Walker, J and Nelson, D and Aneja, VP}, year={2000}, month={Sep}, pages={3527–3534} }