Changes in soil properties along grazing gradients in the mountain and forest steppe, steppe and desert steppe zones of Mongolia

Includes bibliographical references.Presented at the Building resilience of Mongolian rangelands: a trans-disciplinary research conference held on June 9-10, 2015 in Ulaanbaatar, Mongolia.Recent debates about the condition of Mongolia's rangelands and possible causes of rangeland change highlight the need for greater understanding of changes in grassland soil fertility and physical characteristics associated with grazing. As part of a large observational study of grazing effects on different Mongolian ecological zones and soil types (ecological sites), we studied soil characteristics along grazing gradients from winter shelters in the mountain and forest steppe, steppe and desert steppe ecozones of Mongolia. Our objective was to determine how grazing affects soil properties in winter pastures in different ecological zones and ecological sites within zones, based on grazing gradients. Our findings did not support our hypothesis that livestock grazing along a grazing gradient from winter shelters would lead to increased concentrations of nutrients (C, NO3-, P, K and humus) near the shelters. Instead, where soil chemical properties differed with distance, they were lowest close to winter shelters and higher with increasing distance. As hypothesized, we observed greater bulk densities nearer to winter shelters than farther away. Our hypothesis that grazing effects on soil properties would vary among ecological sites also was not supported. Further experimental and observational studies are needed to understand grazing effects on soil properties at different spatial scales and to examine feedbacks between livestock-induced changes in plant communities and soil quality

Measurement of HONO, HNCO, and Other Inorganic Acids by Negative-Ion Proton-Transfer Chemical-Ionization Mass Spectrometry (NI-PT-CIMS): Application to Biomass Burning Emissions

A negative-ion proton-transfer chemical ionization mass spectrometric technique (NI-PT-CIMS), using acetate as the reagent ion, was applied to the measurement of volatile inorganic acids of atmospheric interest: hydrochloric (HCl), nitrous (HONO), nitric (HNO(3)), and isocyanic (HNCO) acids. Gas phase calibrations through the sampling inlet showed the method to be intrinsically sensitive (6-16 cts/pptv), but prone to inlet effects for HNO(3) and HCl. The ion chemistry was found to be insensitive to water vapor concentrations, in agreement with previous studies of carboxylic acids. The inlet equilibration times for HNCO and HONO were 2 to 4s, allowing for measurement in biomass burning studies. Several potential interferences in HONO measurements were examined: decomposition of HNO(3)center dot NO(3)(-) clusters within the CIMS, and NO(2)-water production on inlet surfaces, and were quite minor (\u3c= 1%, 3.3%, respectively). The detection limits of the method were limited by the instrument backgrounds in the ion source and flow tube, and were estimated to range between 16 and 50 pptv (parts per trillion by volume) for a 1 min average. The comparison of HONO measured by CIMS and by in situ FTIR showed good correlation and agreement to within 17%. The method provided rapid and accurate measurements of HNCO and HONO in controlled biomass burning studies, in which both acids were seen to be important products

Wintertime Spatial Distribution of Ammonia and its Emission Sources in the Great Salt Lake Region

Ammonium-containing aerosols are a major component of wintertime air pollution in many densely populated regions around the world. Especially in mountain basins, the formation of persistent cold-air pools (PCAPs) can enhance particulate matter with diameters less than 2.5 µm (PM2.5) to levels above air quality standards. Under these conditions, PM2.5 in the Great Salt Lake region of northern Utah has been shown to be primarily composed of ammonium nitrate; however, its formation processes and sources of its precursors are not fully understood. Hence, it is key to understanding the emission sources of its gas phase precursor, ammonia (NH3). To investigate the formation of ammonium nitrate, a suite of trace gases and aerosol composition were sampled from the NOAA Twin Otter aircraft during the Utah Winter Fine Particulate Study (UWFPS) in January and February 2017. NH3 was measured using a quantum cascade tunable infrared laser differential absorption spectrometer (QC-TILDAS), while aerosol composition, including particulate ammonium (pNH4), was measured with an aerosol mass spectrometer (AMS). The origin of the sampled air masses was investigated using the Stochastic Time-Inverted Lagrangian Transport (STILT) model and combined with an NH3 emission inventory to obtain model-predicted NHx (=NH3+pNH4) enhancements. Enhancements represent the increase in NH3 mixing ratios within the last 24 h due to emissions within the model footprint. Comparison of these NHx enhancements with measured NHx from the Twin Otter shows that modelled values are a factor of 1.6 to 4.4 lower for the three major valleys in the region. Among these, the underestimation is largest for Cache Valley, an area with intensive agricultural activities. We find that one explanation for the underestimation of wintertime emissions may be the seasonality factors applied to NH3 emissions from livestock. An investigation of inter-valley exchange revealed that transport of NH3 between major valleys was limited and PM2.5 in Salt Lake Valley (the most densely populated area in Utah) was not significantly impacted by NH3 from the agricultural areas in Cache Valley. We found that in Salt Lake Valley around two thirds of NHx originated within the valley, while about 30 % originated from mobile sources and 60 % from area source emissions in the region. For Cache Valley, a large fraction of NOx potentially leading to PM2.5 formation may not be locally emitted but mixed in from other counties

An odd oxygen framework for wintertime ammonium nitrate aerosol pollution in urban areas: NOx and VOC control as mitigation strategies

Wintertime ammonium nitrate aerosol pollution is a severe air quality issue affecting both developed and rapidly urbanizing regions from Europe to East Asia. In the US, it is acute in western basins subject to inversions that confine pollutants near the surface. Measurements and modeling of a wintertime pollution episode in Salt Lake City, Utah demonstrates that ammonium nitrate is closely related to photochemical ozone through a common parameter, total odd oxygen, Ox,total. We show that the traditional NOx‐VOC framework for evaluating ozone mitigation strategies also applies to ammonium nitrate. Despite being nitrate‐limited, ammonium nitrate aerosol pollution in Salt Lake City is responsive to VOC control and, counterintuitively, not initially responsive to NOx control. We demonstrate simultaneous nitrate limitation and NOx saturation and suggest this phenomenon may be general. This finding may identify an unrecognized control strategy to address a global public health issue in regions with severe winter aerosol pollution

Rate Coefficients and Clo Radical Yields in the Reaction of O( 1D) With Cclf 2Ccl 2F, Ccl 3Cf 3, Cclf 2Cclf 2, and Ccl 2Fcf 3

Rate coefficients, k, and ClO radical product yields, Y, for the gas-phase reaction of O( 1D) with CClF 2CCl 2F (CFC-113) (k 2), CCl 3CF 3 (CFC-113a) (k 3), CClF 2CClF 2 (CFC-114) (k 4), and CCl 2FCF 3 (CFC-114a) (k 5) at 296 K are reported. Rate coefficients for the loss of O( 1D) were measured using a competitive reaction technique, with n-butane (n-C 4H 10) as the reference reactant, employing pulsed laser photolysis production of O( 1D) combined with laser-induced fluorescence detection of the OH radical temporal profile. Rate coefficients were measured to be k 2 = (2.33 ± 0.40) × 10 -10 cm 3 molecule -1 s -1, k 3 = (2.61 ± 0.40) × 10 -10 cm 3 molecule -1 s -1, k 4 = (1.42 ± 0.25) × 10 -10 cm 3 molecule -1 s -1, and k 5 = (1.62 ± 0.30) × 10 -10 cm 3 molecule -1 s -1. ClO radical product yields for reactions (2)-(5) were measured using pulsed laser photolysis combined with cavity ring-down spectroscopy to be 0.80 ± 0.10, 0.79 ± 0.10, 0.85 ± 0.12, and 0.79 ± 0.10, respectively. The quoted errors in k and Y are at the 2σ (95% confidence) level and include estimated systematic errors. © 2011 Wiley Periodicals, Inc

OH + (<i>E</i>)- and (<i>Z</i>)‑1-Chloro-3,3,3-trifluoropropene‑1 (CF₃CHCHCl) Reaction Rate Coefficients: Stereoisomer-Dependent Reactivity

Rate coefficients for the gas-phase reaction of the OH radical with (<i>E</i>)- and (<i>Z</i>)-CF₃CHCHCl (1-chloro-3,3,3-trifluoropropene-1, HFO-1233zd) (<i>k</i>₁(<i>T</i>) and <i>k</i>₂(<i>T</i>), respectively) were measured under pseudo-first-order conditions in OH over the temperature range 213–376 K. OH was produced by pulsed laser photolysis, and its temporal profile was measured using laser-induced fluorescence. The obtained rate coefficients were independent of pressure between 25 and 100 Torr (He, N₂) with <i>k</i>₁(296 K) = (3.76 ± 0.35) × 10^–13 cm³ molecule^–1 s^–1 and <i>k</i>₂(296 K) = (9.46 ± 0.85) × 10^–13 cm³ molecule^–1 s^–1 (quoted uncertainties are 2σ and include estimated systematic errors). <i>k</i>₂(<i>T</i>) showed a weak non-Arrhenius behavior over this temperature range. The (<i>E</i>)- and (<i>Z</i>)- stereoisomer rate coefficients were found to have opposite temperature dependencies that are well represented by <i>k</i>₁(<i>T</i>) = (1.14 ± 0.15) × 10^–12 exp[(−330 ± 10)/<i>T</i>] cm³ molecule^–1 s^–1 and <i>k</i>₂(<i>T</i>) = (7.22 ± 0.65) × 10^–19 × <i>T</i>² × exp[(800 ± 20)/<i>T</i>] cm³ molecule^–1 s^–1. The present results are compared with a previous room temperature relative rate coefficient study of <i>k</i>₁, and an explanation for the discrepancy is presented. CF₃CHO, HC­(O)­Cl, and CF₃CClO, were observed as stable end-products following the OH radical initiated degradation of (<i>E</i>)- and (<i>Z</i>)-CF₃CHCHCl in the presence of O₂. In addition, chemically activated isomerization was also observed. Atmospheric local lifetimes of (<i>E</i>)- and (<i>Z</i>)-CF₃CHCHCl, due to OH reactive loss, were estimated to be ∼34 and ∼11 days, respectively. Infrared absorption spectra measured in this work were used to estimate radiative efficiencies and well-mixed global warming potentials of ∼10 and ∼3 for (<i>E</i>)- and (<i>Z</i>)-CF₃CHCHCl, respectively, on the 100-year time horizon

Global emission estimates and radiative impact of C[subscript 4]F[subscript 10], C[subscript 5]F[subscript 12], C[subscript 6]F[subscript 14], C[subscript 7]F[subscript 16] and C[subscript 8]F[subscript 18]

Global emission estimates based on new atmospheric observations are presented for the acylic high molecular weight perfluorocarbons (PFCs): decafluorobutane (C[subscript 4]F[subscript 10]), dodecafluoropentane (C[subscript 5]F[subscript 12]), tetradecafluorohexane (C[subscript 6]F[subscript 14]), hexadecafluoroheptane (C[subscript 7]F[subscript 16]) and octadecafluorooctane (C[subscript 8]F[subscript 18]). Emissions are estimated using a 3-dimensional chemical transport model and an inverse method that includes a growth constraint on emissions. The observations used in the inversion are based on newly measured archived air samples that cover a 39-yr period, from 1973 to 2011, and include 36 Northern Hemispheric and 46 Southern Hemispheric samples. The derived emission estimates show that global emission rates were largest in the 1980s and 1990s for C[subscript 4]F[subscript 10] and C[subscript 5]F[subscript 12], and in the 1990s for C[subscript 6]F[subscript 14], C[subscript 7]F[subscript 16] and C[subscript 8]F[subscript 18]. After a subsequent decline, emissions have remained relatively stable, within 20%, for the last 5 yr. Bottom-up emission estimates are available from the Emission Database for Global Atmospheric Research version 4.2 (EDGARv4.2) for C[subscript 4]F[subscript 10], C[subscript 5]F[subscript 12], C[subscript 6]F[subscript 14] and C[subscript 7]F[subscript 16], and inventories of C[subscript 4]F[subscript 10], C[subscript 5]F[subscript 12] and C[subscript 6]F[subscript 14] are reported to the United Nations' Framework Convention on Climate Change (UNFCCC) by Annex 1 countries that have ratified the Kyoto Protocol. The atmospheric measurement-based emission estimates are 20 times larger than EDGARv4.2 for C[subscript 4]F[subscript 10] and over three orders of magnitude larger for C[subscript 5]F[subscript 12] (with 2008 EDGARv4.2 estimates for C[subscript 5]F[subscript 12] at 9.6 kg yr[superscript −1], as compared to 67±53 t yr[superscript −1] as derived in this study). The derived emission estimates for C[subscript 6]F[subscript 14] largely agree with the bottom-up estimates from EDGARv4.2. Moreover, the C[subscript 7]F[subscript 16] emission estimates are comparable to those of EDGARv4.2 at their peak in the 1990s, albeit significant underestimation for the other time periods. There are no bottom-up emission estimates for C[subscript 8]F[subscript 18], thus the emission rates reported here are the first for C[subscript 8]F[subscript 18]. The reported inventories for C[subscript 4]F[subscript 10], C[subscript 5]F[subscript 12] and C[subscript 6]F[subscript 14] to UNFCCC are five to ten times lower than those estimated in this study. In addition, we present measured infrared absorption spectra for C[subscript 7]F[subscript 16] and C[subscript 8]F[subscript 18], and estimate their radiative efficiencies and global warming potentials (GWPs). We find that C[subscript 8]F[subscript 18]'s radiative efficiency is similar to trifluoromethyl sulfur pentafluoride's (SF[subscript 5]F[subscript 3]) at 0.57 W m[superscript −2] ppb[superscript −1], which is the highest radiative efficiency of any measured atmospheric species. Using the 100-yr time horizon GWPs, the total radiative impact of the high molecular weight perfluorocarbons emissions are also estimated; we find the high molecular weight PFCs peak contribution was in 1997 at 24 000 Gg of carbon dioxide (CO[subscript 2]) equivalents and has decreased by a factor of three to 7300 Gg of CO[subscript 2] equivalents in 2010. This 2010 cumulative emission rate for the high molecular weight PFCs is comparable to: 0.02% of the total CO2 emissions, 0.81% of the total hydrofluorocarbon emissions, or 1.07% of the total chlorofluorocarbon emissions projected for 2010 (Velders et al., 2009). In terms of the total PFC emission budget, including the lower molecular weight PFCs, the high molecular weight PFCs peak contribution was also in 1997 at 15.4% and was 6% of the total PFC emissions in CO[subscript 2] equivalents in 2009.NASA Upper Atmospheric Research Program (Grant NNX11AF17G

Measuring acetic and formic acid by proton-transfer-reaction mass spectrometry: sensitivity, humidity dependence, and quantifying interferences

We present a detailed investigation of the factors governing the quantification of formic acid (FA), acetic acid (AA), and their relevant mass analogues by proton-transfer-reaction mass spectrometry (PTR-MS), assess the underlying fragmentation pathways and humidity dependencies, and present a new method for separating FA and AA from their main isobaric interferences. PTR-MS sensitivities towards glycolaldehyde, ethyl acetate, and peroxyacetic acid at <i>m/z</i> 61 are comparable to that for AA; when present, these species will interfere with ambient AA measurements by PTR-MS. Likewise, when it is present, dimethyl ether can interfere with FA measurements. For a reduced electric field (<i>E/N</i>) of 125 Townsend (Td), the PTR-MS sensitivity towards ethanol at <i>m/z</i> 47 is 5–20 times lower than for FA; ethanol will then only be an important interference when present in much higher abundance than FA. Sensitivity towards 2-propanol is <1% of that for AA, so that propanols will not in general represent a significant interference for AA. Hydrated product ions of AA, glycolaldehyde, and propanols occur at <i>m/z</i> 79, which is also commonly used to measure benzene. However, the resulting interference for benzene is only significant when <i>E/N</i> is low (&lesssim;100 Td). Addition of water vapor affects the PTR-MS response to a given compound by (i) changing the yield for fragmentation reactions and (ii) increasing the importance of ligand switching reactions. In the case of AA, sensitivity to the molecular ion increases with humidity at low <i>E/N</i> but decreases with humidity at high <i>E/N</i> due to water-driven fragmentation. Sensitivity towards FA decreases with humidity throughout the full range of <i>E/N</i>. For glycolaldehyde and the alcohols, the sensitivity increases with humidity due to ligand switching reactions (at low <i>E/N</i>) and reduced fragmentation in the presence of water (at high <i>E/N</i>). Their role as interferences will typically be greatest at high humidity. For compounds such as AA where the humidity effect depends strongly on the collisional energy in the drift tube, simple humidity correction factors (<i>X</i>_R) will only be relevant for a specific instrumental configuration. We recommend <i>E/N</i> ~ 125 Td as an effective condition for AA and FA measurements by PTR-MS, as it optimizes between the competing <i>E/N</i>-dependent mechanisms controlling their sensitivities and those of the interfering species. Finally, we present the design and evaluation of an online acid trap for separating AA and FA from their interfering species at <i>m/z</i> 61 and 47, and we demonstrate its performance during a field deployment to St. Louis, USA, during August–September of 2013