Development of a digital mobile solar tracker

Baidar, Sunil; Kille, Natalie; Ortega, Ivan; Sinreich, R.; Thomson, D. S.; Hannigan, James W.; Volkamer, Rainer

doi:10.5194/amt-9-963-2016

Cited by 16 publications

(26 citation statements)

References 22 publications

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“…The CU SOF instrument uses a custom-built digital solar tracker (Baidar et al, 2016), and is described in detail in Kille et al (2017), where a detailed characterization of the NH 3 and C 2 H 6 retrievals is also 10.1029/2019GL082132…”

Section: Retrievalsmentioning

confidence: 99%

Separation of Methane Emissions From Agricultural and Natural Gas Sources in the Colorado Front Range

Kille

Chiu

Frey

et al. 2019

Geophysical Research Letters

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This proof‐of‐concept study demonstrates that methane (CH4) emissions from natural gas (NG) and agriculture can be disentangled using the concept of excess column observations. A network of cost‐effective sensors measured excess column‐averaged dry‐air mole fractions for CH4 (ΔXCH4), ethane (ΔXC2H6 as NG tracer), and ammonia (ΔXNH3 from agriculture) in the Denver‐Julesburg Basin during March 2015. ΔXCH4 varied up to 17 ppb and was >3 times higher with winds from directions where NG is produced. The ΔXCH4 variance is explained by variations in the C2H6‐NH3 tracer pair, attributing 63 ± 17% to NG, 25 ± 10% to agriculture, and 12 ± 12% to other sources. The ratios ΔXC2H6/ΔXCH4 (16 ± 2%; indicates wet NG) and ΔXNH3/ΔXCH4 (43 ± 12%) were compatible with in situ measured ratios. Excess columns are independent of boundary layer height, characterize gases in the open atmosphere, are inherently calibrated, average over extended spatial scales, and provide a complementary perspective to quantify and attribute CH4 emissions on regional scales.

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Section: Retrievalsmentioning

confidence: 99%

Separation of Methane Emissions From Agricultural and Natural Gas Sources in the Colorado Front Range

Kille

Chiu

Frey

et al. 2019

Geophysical Research Letters

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“…The SOF method is complementary to other techniques used to quantify emissions, such as in situ measurements, or stationary deployment of several commercial EM27/SUN Fourier transform spectrometer (FTS) around an area source (Hase et al, 2015;Chen et al, 2016). In situ measurements, or open-path eddy covariance studies (Baum et al, 2008), provide more localized information and require access to the site of interest. Micrometeorological gradient methods require assumptions of homogeneity (Todd et al, 2008).…”

Section: Introductionmentioning

confidence: 99%

The CU mobile Solar Occultation Flux instrument: structure functions and emission rates of NH3, NO2 and C2H6

et al. 2017

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Abstract. We describe the University of Colorado mobile Solar Occultation Flux instrument (CU mobile SOF). The instrument consists of a digital mobile solar tracker that is coupled to a Fourier transform spectrometer (FTS) of 0.5 cm−1 resolution and a UV–visible spectrometer (UV–vis) of 0.55 nm resolution. The instrument is used to simultaneously measure the absorption of ammonia (NH3), ethane (C2H6) and nitrogen dioxide (NO2) along the direct solar beam from a moving laboratory. These direct-sun observations provide high photon flux and enable measurements of vertical column densities (VCDs) with geometric air mass factors, high temporal resolution of 2 s and spatial resolution of 5–19 m. It is shown that the instrument line shape (ILS) of the FTS is independent of the azimuth and elevation angle pointing of the solar tracker. Further, collocated measurements next to a high-resolution FTS at the National Center for Atmospheric Research (HR-NCAR-FTS) show that the CU mobile SOF measurements of NH3 and C2H6 are precise and accurate; the VCD error at high signal to noise ratio is 2–7 %. During the Front Range Air Pollution and Photochemistry Experiment (FRAPPE) from 21 July to 3 September 2014 in Colorado, the CU mobile SOF instrument measured median (minimum, maximum) VCDs of 4.3 (0.5, 45)  ×  1016 molecules cm−2 NH3, 0.30 (0.06, 2.23)  ×  1016 molecules cm−2 NO2 and 3.5 (1.5, 7.7)  ×  1016 molecules cm−2 C2H6. All gases were detected in larger 95 % of the spectra recorded in urban, semi-polluted rural and remote rural areas of the Colorado Front Range. We calculate structure functions based on VCDs, which describe the variability of a gas column over distance, and find the largest variability for NH3. The structure functions suggest that currently available satellites resolve about 10 % of the observed NH3 and NO2 VCD variability in the study area. We further quantify the trace gas emission fluxes of NH3 and C2H6 and production rates of NO2 from concentrated animal feeding operations (CAFO) using the mass balance method, i.e., the closed-loop vector integral of the VCD times wind speed along the drive track. Excellent reproducibility is found for NH3 fluxes and also, to a lesser extent, NO2 production rates on 2 consecutive days; for C2H6 the fluxes are affected by variable upwind conditions. Average emission factors were 12.0 and 11.4 gNH3 h−1 head−1 at 30 °C for feedlots with a combined capacity for ∼  54 000 cattle and a dairy farm of ∼  7400 cattle; the pooled rate of 11.8 ± 2.0 gNH3 h−1 head−1 is compatible with the upper range of literature values. At this emission rate the NH3 source from cattle in Weld County, CO (535 766 cattle), could be underestimated by a factor of 2–10. CAFO soils are found to be a significant source of NOx. The NOx source accounts for ∼  1.2 % of the N flux in NH3 and has the potential to add ∼  10 % to the overall NOx emissions in Weld County and double the NOx source in remote areas. This potential of CAFO to influence ambient NOx concentrations on the regional scale is relevant because O3 formation is NOx sensitive in the Colorado Front Range. Emissions of NH3 and NOx are relevant for the photochemical O3 and secondary aerosol formation.

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“…The first phase of the Department of Energy (DOE) TCAP field campaign took place at Cape Cod, MA, during the summer of 2012 (Berg et al, 2016). TCAP was designed to pro- vide a comprehensive characterization of the aerosol direct and indirect effects under urban emission influences near the eastern coast of North America (over Cape Cod, MA) and to contrast it with observations in pristine conditions over the Atlantic Ocean.…”

Section: The Two-column Aerosol Project (Tcap) Field Campaignmentioning

confidence: 99%

“…TCAP was designed to pro- vide a comprehensive characterization of the aerosol direct and indirect effects under urban emission influences near the eastern coast of North America (over Cape Cod, MA) and to contrast it with observations in pristine conditions over the Atlantic Ocean. An extensive set of aerosol measurements was conducted aboard two research aircrafts (DOE G-1 and NASA B200) and with the DOE Atmospheric Radiation Measurement (ARM) ground mobile facility (located over Cape Cod, MA, USA); for details see Berg et al (2016). The CU 2-D-MAX-DOAS was deployed at the ARM ground site from 1 July to 13 August 2012 to test its innovative capabilities to measure aerosol optical properties and trace gases simultaneously with a single instrument.…”

Section: The Two-column Aerosol Project (Tcap) Field Campaignmentioning

confidence: 99%

“…The CU 2-D-MAX-DOAS was deployed at the ARM ground site from 1 July to 13 August 2012 to test its innovative capabilities to measure aerosol optical properties and trace gases simultaneously with a single instrument. Here, we focus primarily on 22 July 2012 due to its low AOD and cloud-free conditions and the available complementary data (Berg et al, 2016;Ortega et al, 2016). The retrieval approach is also applied for a high AOD case study on 17 July 2012.…”

Section: The Two-column Aerosol Project (Tcap) Field Campaignmentioning

confidence: 99%

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The CU 2-D-MAX-DOAS instrument – Part 2: Raman scattering probability measurements and retrieval of aerosol optical properties

et al. 2016

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Abstract. The multiannual global mean of aerosol optical depth at 550 nm (AOD550) over land is ∼ 0.19, and that over oceans is ∼ 0.13. About 45 % of the Earth surface shows AOD550 smaller than 0.1. There is a need for measurement techniques that are optimized to measure aerosol optical properties under low AOD conditions. We present an inherently calibrated retrieval (i.e., no need for radiance calibration) to simultaneously measure AOD and the aerosol phase function parameter, g, based on measurements of azimuth distributions of the Raman scattering probability (RSP), the near-absolute rotational Raman scattering (RRS) intensity. We employ radiative transfer model simulations to show that for solar azimuth RSP measurements at solar elevation and solar zenith angle (SZA) smaller than 80°, RSP is insensitive to the vertical distribution of aerosols and maximally sensitive to changes in AOD and g under near-molecular scattering conditions. The University of Colorado two-dimensional Multi-AXis Differential Optical Absorption Spectroscopy (CU 2-D-MAX-DOAS) instrument was deployed as part of the Two Column Aerosol Project (TCAP) at Cape Cod, MA, during the summer of 2012 to measure direct sun spectra and RSP from scattered light spectra at solar relative azimuth angles (SRAAs) between 5 and 170°. During two case study days with (1) high aerosol load (17 July, 0.3  <  AOD430 < 0.6) and (2) near-molecular scattering conditions (22 July, AOD430 < 0.13) we compare RSP-based retrievals of AOD430 and g with data from a co-located CIMEL sun photometer, Multi-Filter Rotating Shadowband Radiometer (MFRSR), and an airborne High Spectral Resolution Lidar (HSRL-2). The average difference (relative to DOAS) for AOD430 is +0.012 ± 0.023 (CIMEL), −0.012 ± 0.024 (MFRSR), −0.011 ± 0.014 (HSRL-2), and +0.023 ± 0.013 (CIMELAOD − MFRSRAOD) and yields the following expressions for correlations between different instruments: DOASAOD = −(0.019 ± 0.006) + (1.03 ± 0.02) ×  CIMELAOD (R2 = 0.98), DOASAOD = −(0.006 ± 0.005) + (1.08 ± 0.02) ×  MFRSRAOD (R2 = 0.98), and CIMELAOD = (0.013 ± 0.004) + (1.05 ± 0.01) ×  MFRSRAOD (R2 = 0.99). The average g measured by DOAS on both days was 0.66 ± 0.03, with a difference of 0.014 ± 0.05 compared to CIMEL. Active steps to minimize the error in the RSP help to reduce the uncertainty in retrievals of AOD and g. As AOD decreases and SZA increases, the RSP signal-to-noise ratio increases. At AOD430  ∼  0.4 and 0.10 the absolute AOD errors are ∼ 0.014 and 0.003 at 70° SZA and 0.02 and 0.004 at 35° SZA. Inherently calibrated, precise AOD and g measurements are useful to better characterize the aerosol direct effect in urban polluted and remote pristine environments.

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Development of a digital mobile solar tracker

Cited by 16 publications

References 22 publications

Separation of Methane Emissions From Agricultural and Natural Gas Sources in the Colorado Front Range

Separation of Methane Emissions From Agricultural and Natural Gas Sources in the Colorado Front Range

The CU mobile Solar Occultation Flux instrument: structure functions and emission rates of NH<sub>3</sub>, NO<sub>2</sub> and C<sub>2</sub>H<sub>6</sub>

The CU 2-D-MAX-DOAS instrument – Part 2: Raman scattering probability measurements and retrieval of aerosol optical properties

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Development of a digital mobile solar tracker

Cited by 16 publications

References 22 publications

Separation of Methane Emissions From Agricultural and Natural Gas Sources in the Colorado Front Range

Separation of Methane Emissions From Agricultural and Natural Gas Sources in the Colorado Front Range

The CU mobile Solar Occultation Flux instrument: structure functions and emission rates of NH&lt;sub&gt;3&lt;/sub&gt;, NO&lt;sub&gt;2&lt;/sub&gt; and C&lt;sub&gt;2&lt;/sub&gt;H&lt;sub&gt;6&lt;/sub&gt;

The CU 2-D-MAX-DOAS instrument – Part 2: Raman scattering probability measurements and retrieval of aerosol optical properties

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About

The CU mobile Solar Occultation Flux instrument: structure functions and emission rates of NH<sub>3</sub>, NO<sub>2</sub> and C<sub>2</sub>H<sub>6</sub>