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  1. Portable nitrous oxide sensor for understanding agricultural and soil emissions

    Nitrous oxide (N2O) is the third most important greenhouse gas (GHG,) with an atmospheric lifetime of ~114 years and a global warming impact ~300 times greater than that of carbon dioxide. The main cause of nitrous oxide’s atmospheric increase is anthropogenic emissions, and over 80% of the current global anthropogenic flux is related to agriculture, including associated land-use change. An accurate assessment of N2O emissions from agriculture is vital not only for understanding the global N2O balance and its impact on climate but also for designing crop systems with lower GHG emissions. Such assessments are currently hampered by the lackmore » of instrumentation and methodologies to measure ecosystem-level fluxes at appropriate spatial and temporal scales. Southwest Sciences and Princeton University are developing and testing new open-path eddy covariance instrumentation for continuous and fast (10 Hz) measurement of nitrous oxide emissions. An important advance, now being implemented, is the use of new mid-infrared laser sources that enable the development of exceptionally low power (<10 W) compact instrumentation that can be used even in remote sites lacking in power. The instrumentation will transform the ability to measure and understand ecosystem-level nitrous oxide fluxes. The Phase II results included successful extended field testing of prototype flux instruments, based on quantum cascade lasers, in collaboration with Michigan State University. Results of these tests demonstrated a flux detection limit of 5 µg m-2 s-1 and showed excellent agreement and correlation with measurements using chamber techniques. Initial tests of an instrument using an interband cascade laser (ICL) were performed, verifying that an order of magnitude reduction in instrument power requirements can be realized. These results point toward future improvements and testing leading to introduction of a commercial open path instrument for N2O flux measurements that is truly portable and cost-effective. The technology developed on this project is especially groundbreaking as it could be widely applied across FLUXNET and AmeriFlux sites (>1200 worldwide) for direct measurements of N2O exchange. The technology can be more broadly applied to gas monitoring requirements in industry, environmental monitoring, health and safety, etc.« less
  2. Ammonia and methane dairy emissions in the San Joaquin Valley of California from individual feedlot to regional scale

    Agricultural ammonia (NH 3) emissions are highly uncertain, with high spatiotemporal variability and a lack of widespread in situ measurements. Regional NH 3 emission estimates using mass balance or emission ratio approaches are uncertain due to variable NH 3 sources and sinks as well as unknown plume correlations with other dairy source tracers. We characterize the spatial distributions of NH 3 and methane (CH 4) dairy plumes using in situ surface and airborne measurements in the Tulare dairy feedlot region of the San Joaquin Valley, California, during the NASA Deriving Information on Surface conditions from Column and Vertically Resolved Observationsmore » Relevant to Air Quality 2013 field campaign. Surface NH 3 and CH 4 mixing ratios exhibit large variability with maxima localized downwind of individual dairy feedlots. The geometric mean NH 3:CH 4 enhancement ratio derived from surface measurements is 0.15 ± 0.03 ppmv ppmv –1. Individual dairy feedlots with spatially distinct NH 3 and CH 4 source pathways led to statistically significant correlations between NH 3 and CH 4 in 68% of the 69 downwind plumes sampled. At longer sampling distances, the NH 3:CH 4 enhancement ratio decreases 20–30%, suggesting the potential for NH 3 deposition as a loss term for plumes within a few kilometers downwind of feedlots. Aircraft boundary layer transect measurements directly above surface mobile measurements in the dairy region show comparable gradients and geometric mean enhancement ratios within measurement uncertainties, even when including NH 3 partitioning to submicron particles. Individual NH 3 and CH 4 plumes sampled at close proximity where losses are minimal are not necessarily correlated due to lack of mixing and distinct source pathways. As a result, our analyses have important implications for constraining NH 3 sink and plume variability influences on regional NH 3 emission estimates and for improving NH 3 emission inventory spatial allocations.« less
  3. Active and widespread halogen chemistry in the tropical and subtropical free troposphere

    Halogens in the troposphere are increasingly recognized as playing an important role for atmospheric chemistry, and possibly climate. Bromine and iodine react catalytically to destroy ozone (O 3), oxidize mercury, and modify oxidative capacity that is relevant for the lifetime of greenhouse gases. Most of the tropospheric O 3 and methane (CH 4) loss occurs at tropical latitudes. Here we report simultaneous measurements of vertical profiles of bromine oxide (BrO) and iodine oxide (IO) in the tropical and subtropical free troposphere (10°N to 40°S), and show that these halogens are responsible for 34% of the column-integrated loss of tropospheric Omore » 3. The observed BrO concentrations increase strongly with altitude (~3.4 pptv at 13.5 km), and are 2–4 times higher than predicted in the tropical free troposphere. BrO resembles model predictions more closely in stratospheric air. The largest model low bias is observed in the lower tropical transition layer (TTL) over the tropical eastern Pacific Ocean, and may reflect a missing inorganic bromine source supplying an additional 2.5–6.4 pptv total inorganic bromine (Br y), or model overestimated Bry wet scavenging. Our results highlight the importance of heterogeneous chemistry on ice clouds, and imply an additional Bry source from the debromination of sea salt residue in the lower TTL. The observed levels of bromine oxidize mercury up to 3.5 times faster than models predict, possibly increasing mercury deposition to the ocean. Lastly, the halogen-catalyzed loss of tropospheric O 3 needs to be considered when estimating past and future ozone radiative effects.« less
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  4. Calibration of the Total Carbon Column Observing Network using Aircraft Profile Data

    The Total Carbon Column Observing Network (TCCON) produces precise measurements of the column average dry-air mole fractions of CO{sub 2}, CO, CH{sub 4}, N{sub 2}O and H{sub 2}O at a variety of sites worldwide. These observations rely on spectroscopic parameters that are not known with sufficient accuracy to compute total columns that can be used in combination with in situ measure ments. The TCCON must therefore be calibrated to World Meteorological Organization (WMO) in situ trace gas measurement scales. We present a calibration of TCCON data using WMO-scale instrumentation aboard aircraft that measured profiles over four TCCON stations during 2008more » and 2009. The aircraft campaigns are the Stratosphere-Troposphere Analyses of Regional Transport 2008 (START-08), which included a profile over the Park Falls site, the HIAPER Pole-to-Pole Observations (HIPPO-1) campaign, which included profiles over the Lamont and Lauder sites, a series of Learjet profiles over the Lamont site, and a Beechcraft King Air profile over the Tsukuba site. These calibrations are compared with similar observations made during the INTEX-NA (2004), COBRA-ME (2004) and TWP-ICE (2006) campaigns. A single, global calibration factor for each gas accurately captures the TCCON total column data within error.« less

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"Zondlo, Mark"

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