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J R Herman - One of the best experts on this subject based on the ideXlab platform.
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underestimation of column no 2 amounts from the omi satellite compared to diurnally varying ground based retrievals from multiple Pandora spectrometer instruments
Atmospheric Measurement Techniques, 2019Co-Authors: J R Herman, Nader Abuhassan, Manvendra K Dubey, Marcelo Raponi, Maria TzortziouAbstract:Abstract. Retrievals of total column NO2 ( TCNO2 ) are compared for 14 sites from the Ozone Measuring Instrument (OMI using OMNO2-NASA v3.1) on the AURA satellite and from multiple ground-based Pandora spectrometer instruments making direct-sun measurements. While OMI accurately provides the daily global distribution of retrieved TCNO2 , OMI almost always underestimates the local amount of TCNO2 by 50 % to 100 % in polluted areas, while occasionally the daily OMI value exceeds that measured by Pandora at very clean sites. Compared to local ground-based or aircraft measurements, OMI cannot resolve spatially variable TCNO2 pollution within a city or urban areas, which makes it less suitable for air quality assessments related to human health. In addition to systematic underestimates in polluted areas, OMI's selected 13:30 Equator crossing time polar orbit causes it to miss the frequently much higher values of TCNO2 that occur before or after the OMI overpass time. Six discussed Northern Hemisphere Pandora sites have multi-year data records (Busan, Seoul, Washington DC, Waterflow, New Mexico, Boulder, Colorado, and Mauna Loa), and one site in the Southern Hemisphere (Buenos Aires, Argentina). The first four of these sites and Buenos Aires frequently have high TCNO2 ( TCNO2 > 0.5 DU). Eight additional sites have shorter-term data records in the US and South Korea. One of these is a 1-year data record from a highly polluted site at City College in New York City with pollution levels comparable to Seoul, South Korea. OMI-estimated air mass factor, surface reflectivity, and the OMI 24 km × 13 km FOV (field of view) are three factors that can cause OMI to underestimate TCNO2 . Because of the local inhomogeneity of NOx emissions, the large OMI FOV is the most likely factor for consistent underestimates when comparing OMI TCNO2 to retrievals from the small Pandora effective FOV (measured in m 2) calculated from the solar diameter of 0.5 ∘ .
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nitrogen dioxide and formaldehyde measurements from the geostationary coastal and air pollution events geo cape airborne simulator over houston texas
Atmospheric Measurement Techniques, 2018Co-Authors: C R Nowlan, S J Janz, M G Kowalewski, K Chance, M B Follettecook, A Fried, Gonzalo Gonzalez Abad, J R HermanAbstract:Abstract. The GEOstationary Coastal and Air Pollution Events (GEO-CAPE) Airborne Simulator (GCAS) was developed in support of NASA's decadal survey GEO-CAPE geostationary satellite mission. GCAS is an airborne push-broom remote-sensing instrument, consisting of two channels which make hyperspectral measurements in the ultraviolet/visible (optimized for air quality observations) and the visible–near infrared (optimized for ocean color observations). The GCAS instrument participated in its first intensive field campaign during the Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) campaign in Texas in September 2013. During this campaign, the instrument flew on a King Air B-200 aircraft during 21 flights on 11 days to make air quality observations over Houston, Texas. We present GCAS trace gas retrievals of nitrogen dioxide ( NO2 ) and formaldehyde ( CH2O ), and compare these results with trace gas columns derived from coincident in situ profile measurements of NO2 and CH2O made by instruments on a P-3B aircraft, and with NO2 observations from ground-based Pandora spectrometers operating in direct-sun and scattered light modes. GCAS tropospheric column measurements correlate well spatially and temporally with columns estimated from the P-3B measurements for both NO2 ( r2=0.89 ) and CH2O ( r2=0.54 ) and with Pandora direct-sun ( r2=0.85 ) and scattered light ( r2=0.94 ) observed NO2 columns. Coincident GCAS columns agree in magnitude with NO2 and CH2O P-3B-observed columns to within 10 % but are larger than scattered light Pandora tropospheric NO2 columns by 33 % and direct-sun Pandora NO2 columns by 50 %.
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retrieval accuracy of hcho vertical column density from ground based direct sun measurement and first hcho column measurement using Pandora
Remote Sensing, 2018Co-Authors: Junsung Park, J R Herman, Hanlim Lee, Jhoon Kim, Woogyung Kim, Hyunkee Hong, Wonei Choi, Jiwon Yang, Daewon KimAbstract:In the present study, we investigate the effects of signal to noise (SNR), slit function (FWHM), and aerosol optical depth (AOD) on the accuracy of formaldehyde (HCHO) vertical column density (HCHOVCD) using the ground-based direct-sun synthetic radiance based on differential optical absorption spectroscopy (DOAS). We found that the effect of SNR on HCHO retrieval accuracy is larger than those of FWHM and AOD. When SNR = 650 (1300), FWHM = 0.6, and AOD = 0.2, the absolute percentage difference (APD) between the true HCHOVCD values and those retrieved ranges from 54 (30%) to 5% (1%) for the HCHOVCD of 5.0 × 1015 and 1.1 × 1017 molecules cm−2, respectively. Interestingly, the maximum AOD effect on the HCHO accuracy was found for the HCHOVCD of 3.0 × 1016 molecules cm−2. In addition, we carried out the first ground-based direct-sun measurements in the ultraviolet (UV) wavelength range to retrieve the HCHOVCD using Pandora in Seoul. The HCHOVCD was low at 12:00 p.m. local time (LT) in all seasons, whereas it was high in the morning (10:00 a.m. LT) and late afternoon (4:00 p.m. LT), except in winter. The maximum HCHOVCD values were 2.68 × 1016, 3.19 × 1016, 2.00 × 1016, and 1.63 × 1016 molecules cm−2 at 10:00 a.m. LT in spring, 10:00 a.m. LT in summer, 1:00 p.m. LT in autumn, and 9:00 a.m. LT in winter, respectively. The minimum values of Pandora HCHOVCD were 1.63 × 1016, 2.23 × 1016, 1.26 × 1016, and 0.82 × 1016 molecules cm−2 at around 1:45 p.m. LT in spring, summer, autumn, and winter, respectively. This seasonal pattern of high values in summer and low values in winter implies that photo-oxidation plays an important role in HCHO production. The correlation coefficient (R) between the monthly HCHOVCD values from Pandora and those from the Ozone Monitoring Instrument (OMI) is 0.61, and the slope is 1.25.
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spatial and temporal variability of ozone and nitrogen dioxide over a major urban estuarine ecosystem
Journal of Atmospheric Chemistry, 2015Co-Authors: Maria Tzortziou, J R Herman, Alexander Cede, Christopher P Loughner, Nader Abuhassan, Sheenali NaikAbstract:Spatial and temporal dynamics in trace gas pollutants were examined over a major urban estuarine ecosystem, using a new network of ground-based Pandora spectrometers deployed at strategic locations along the Washington-Baltimore corridor and the Chesapeake Bay. Total column ozone (TCO3) and nitrogen dioxide (TCNO2) were measured during NASA’s DISCOVER-AQ and GeoCAPE-CBODAQ campaigns in July 2011. The Pandora network provided high-resolution information on air-quality variability, local pollution conditions, large-scale meteorological influences, and interdependencies of ozone and its major precursor, NO2. Measurements were used to compare with air-quality model simulations (CMAQ), evaluate Aura-OMI satellite retrievals, and assess advantages and limitations of space-based observations under a range of conditions. During the campaign, TCNO2 varied by an order of magnitude, both spatially and temporally. Although fairly constant in rural regions, TCNO2 showed clear diurnal and weekly patterns in polluted urban areas caused by changes in near-surface emissions. With a coarse resolution and an overpass at around 13:30 local time, OMI cannot detect this strong variability in NO2, missing pollution peaks from industrial and rush hour activities. Not as highly variable as NO2, TCO3 was mostly affected by large-scale meteorological patterns as observed by OMI. A clear weekly cycle in TCO3, with minima over the weekend, was due to a combination of weekly weather patterns and changes in near-surface NOx emissions. A Pandora instrument intercomparison under the same conditions at GSFC showed excellent agreement, within ±4.8DU for TCO3 and ±0.07DU for TCNO2 with no air-mass-factor dependence, suggesting that observed variability during the campaign was real.
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comparison of ozone retrievals from the Pandora spectrometer system and dobson spectrophotometer in boulder colorado
Atmospheric Measurement Techniques, 2015Co-Authors: J R Herman, Alexander Cede, Nader Abuhassan, R Evans, Irina Petropavlovskikh, Glen McconvilleAbstract:Abstract. A comparison of retrieved total column ozone (TCO) amounts between the Pandora #34 spectrometer system and the Dobson #061 spectrophotometer from direct-sun observations was performed on the roof of the Boulder, Colorado, NOAA building. This paper, part of an ongoing study, covers a 1-year period starting on 17 December 2013. Both the standard Dobson and Pandora TCO retrievals required a correction, TCOcorr = TCO (1 + C(T)), using a monthly varying effective ozone temperature, TE, derived from a temperature and ozone profile climatology. The correction is used to remove a seasonal difference caused by using a fixed temperature in each retrieval algorithm. The respective corrections C(TE) are CPandora = 0.00333(TE-225) and CDobson = -0.0013(TE-226.7) per degree K. After the applied corrections removed most of the seasonal retrieval dependence on ozone temperature, TCO agreement between the instruments was within 1 % for clear-sky conditions. For clear-sky observations, both co-located instruments tracked the day-to-day variation in total column ozone amounts with a correlation of r2 = 0.97 and an average offset of 1.1 ± 5.8 DU. In addition, the Pandora TCO data showed 0.3 % annual average agreement with satellite overpass data from AURA/OMI (Ozone Monitoring Instrument) and 1 % annual average offset with Suomi-NPP/OMPS (Suomi National Polar-orbiting Partnership, the nadir viewing portion of the Ozone Mapper Profiler Suite).
Maria Tzortziou - One of the best experts on this subject based on the ideXlab platform.
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underestimation of column no 2 amounts from the omi satellite compared to diurnally varying ground based retrievals from multiple Pandora spectrometer instruments
Atmospheric Measurement Techniques, 2019Co-Authors: J R Herman, Nader Abuhassan, Manvendra K Dubey, Marcelo Raponi, Maria TzortziouAbstract:Abstract. Retrievals of total column NO2 ( TCNO2 ) are compared for 14 sites from the Ozone Measuring Instrument (OMI using OMNO2-NASA v3.1) on the AURA satellite and from multiple ground-based Pandora spectrometer instruments making direct-sun measurements. While OMI accurately provides the daily global distribution of retrieved TCNO2 , OMI almost always underestimates the local amount of TCNO2 by 50 % to 100 % in polluted areas, while occasionally the daily OMI value exceeds that measured by Pandora at very clean sites. Compared to local ground-based or aircraft measurements, OMI cannot resolve spatially variable TCNO2 pollution within a city or urban areas, which makes it less suitable for air quality assessments related to human health. In addition to systematic underestimates in polluted areas, OMI's selected 13:30 Equator crossing time polar orbit causes it to miss the frequently much higher values of TCNO2 that occur before or after the OMI overpass time. Six discussed Northern Hemisphere Pandora sites have multi-year data records (Busan, Seoul, Washington DC, Waterflow, New Mexico, Boulder, Colorado, and Mauna Loa), and one site in the Southern Hemisphere (Buenos Aires, Argentina). The first four of these sites and Buenos Aires frequently have high TCNO2 ( TCNO2 > 0.5 DU). Eight additional sites have shorter-term data records in the US and South Korea. One of these is a 1-year data record from a highly polluted site at City College in New York City with pollution levels comparable to Seoul, South Korea. OMI-estimated air mass factor, surface reflectivity, and the OMI 24 km × 13 km FOV (field of view) are three factors that can cause OMI to underestimate TCNO2 . Because of the local inhomogeneity of NOx emissions, the large OMI FOV is the most likely factor for consistent underestimates when comparing OMI TCNO2 to retrievals from the small Pandora effective FOV (measured in m 2) calculated from the solar diameter of 0.5 ∘ .
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omi satellite and ground based Pandora observations and their application to surface no2 estimations at terrestrial and marine sites
Journal of Geophysical Research, 2017Co-Authors: Maria Tzortziou, Debra E Kollonige, Anne M Thompson, Miroslav Josipovic, J P Beukes, Roelof BurgerAbstract:The Pandora spectrometer that uses direct-sun measurements to derive total column amounts of gases provides an approach for (1) validation of satellite instruments and (2) monitoring of total column (TC) ozone (O3) and nitrogen dioxide (NO2). We use for the first time Pandora and OMI observations to estimate surface NO2 over marine and terrestrial sites downwind of urban pollution and compared with in situ measurements during campaigns in contrasting regions: (1) the South African Highveld (at Welgegund, 26°34'10"S, 26°56'21"E, 1480 m asl, ~120 km south-west of the Johannesburg-Pretoria megacity); (2) shipboard US mid-Atlantic coast during the 2014 Deposition of Atmospheric Nitrogen to Coastal Ecosystems (DANCE) cruise. In both cases there were no local NOx sources, but intermittent regional pollution influences. For TC NO2, OMI and Pandora difference is ~ 20% with Pandora higher most times. Surface NO2 values estimated from OMI and Pandora columns are compared to in situ NO2 for both locations. For Welgegund, the planetary boundary layer (PBL) height, used in converting column to surface NO2 value, has been estimated by three methods: co-located Atmospheric InfraRed Sounder (AIRS) observations; a model simulation; radiosonde data from Irene, 150 km northeast of the site. AIRS PBL heights agree within 10% of radiosonde-derived values. Absolute differences between Pandora- and OMI-estimated surface NO2 and the in situ data are better at the terrestrial site (~0.5ppbv and ~1 ppbv or greater, respectively) than under clean marine air conditions, with differences usually >3 ppbv. Cloud cover and PBL variability can influence these estimations.
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spatial and temporal variability of ozone and nitrogen dioxide over a major urban estuarine ecosystem
Journal of Atmospheric Chemistry, 2015Co-Authors: Maria Tzortziou, J R Herman, Alexander Cede, Christopher P Loughner, Nader Abuhassan, Sheenali NaikAbstract:Spatial and temporal dynamics in trace gas pollutants were examined over a major urban estuarine ecosystem, using a new network of ground-based Pandora spectrometers deployed at strategic locations along the Washington-Baltimore corridor and the Chesapeake Bay. Total column ozone (TCO3) and nitrogen dioxide (TCNO2) were measured during NASA’s DISCOVER-AQ and GeoCAPE-CBODAQ campaigns in July 2011. The Pandora network provided high-resolution information on air-quality variability, local pollution conditions, large-scale meteorological influences, and interdependencies of ozone and its major precursor, NO2. Measurements were used to compare with air-quality model simulations (CMAQ), evaluate Aura-OMI satellite retrievals, and assess advantages and limitations of space-based observations under a range of conditions. During the campaign, TCNO2 varied by an order of magnitude, both spatially and temporally. Although fairly constant in rural regions, TCNO2 showed clear diurnal and weekly patterns in polluted urban areas caused by changes in near-surface emissions. With a coarse resolution and an overpass at around 13:30 local time, OMI cannot detect this strong variability in NO2, missing pollution peaks from industrial and rush hour activities. Not as highly variable as NO2, TCO3 was mostly affected by large-scale meteorological patterns as observed by OMI. A clear weekly cycle in TCO3, with minima over the weekend, was due to a combination of weekly weather patterns and changes in near-surface NOx emissions. A Pandora instrument intercomparison under the same conditions at GSFC showed excellent agreement, within ±4.8DU for TCO3 and ±0.07DU for TCNO2 with no air-mass-factor dependence, suggesting that observed variability during the campaign was real.
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high precision absolute total column ozone measurements from the Pandora spectrometer system comparisons with data from a brewer double monochromator and aura omi
Journal of Geophysical Research, 2012Co-Authors: Maria Tzortziou, J R Herman, Alexander Cede, Nader AbuhassanAbstract:We present new, high precision, high temporal resolution measurements of total column ozone (TCO) amounts derived from ground-based direct-sun irradiance measurements using our recently deployed Pandora single-grating spectrometers. Pandora's small size and portability allow deployment at multiple sites within an urban air-shed and development of a ground-based monitoring network for studying small-scale atmospheric dynamics, spatial heterogeneities in trace gas distribution, local pollution conditions, photochemical processes and interdependencies of ozone and its major precursors. Results are shown for four mid- to high-latitude sites where different Pandora instruments were used. Comparisons with a well calibrated double-grating Brewer spectrometer over a period of more than a year in Greenbelt MD showed excellent agreement and a small bias of approximately 2 DU (or, 0.6%). This was constant with slant column ozone amount over the full range of observed solar zenith angles (15-80), indicating adequate Pandora stray light correction. A small (1-2%) seasonal difference was found, consistent with sensitivity studies showing that the Pandora spectral fitting TCO retrieval has a temperature dependence of 1% per 3K, with an underestimation in temperature (e.g., during summer) resulting in an underestimation of TCO. Pandora agreed well with Aura-OMI (Ozone Measuring Instrument) satellite data, with average residuals of <1% at the different sites when the OMI view was within 50 km from the Pandora location and OMI-measured cloud fraction was <0.2. The frequent and continuous measurements by Pandora revealed significant short-term (hourly) temporal changes in TCO, not possible to capture by sun-synchronous satellites, such as OMI, alone.
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no2 column amounts from ground based Pandora and mfdoas spectrometers using the direct sun doas technique intercomparisons and application to omi validation
Journal of Geophysical Research, 2009Co-Authors: J R Herman, Maria Tzortziou, Alexander Cede, E Spinei, G H Mount, Nader AbuhassanAbstract:[1] Vertical column amounts of nitrogen dioxide, C(NO 2 ), are derived from ground-based direct solar irradiance measurements using two new and independently developed spectrometer systems, Pandora (Goddard Space Flight Center) and MFDOAS (Washington State University). We discuss the advantages of C(NO 2 ) retrievals based on Direct Sun - Differential Optical Absorption Spectroscopy (DS-DOAS). The C(NO 2 ) data are presented from field campaigns using Pandora at Aristotle University (AUTH), Thessaloniki, Greece; a second field campaign involving both new instruments at Goddard Space Flight Center (GSFC), Greenbelt, Maryland; a Pandora time series from December 2006 to October 2008 at GSFC; and a MFDOAS time series for spring 2008 at Pacific Northwest National Laboratory (PNNL), Richland, Washington. Pandora and MFDOAS were compared at GFSC and found to closely agree, with both instruments having a clear-sky precision of 0.01 DU (1 DU = 2.67 × 10 16 molecules/cm 2 ) and a nominal accuracy of 0.1 DU. The high precision is obtained from careful laboratory characterization of the spectrometers (temperature sensitivity, slit function, pixel to pixel radiometric calibration, and wavelength calibration), and from sufficient measurement averaging to reduce instrument noise. The accuracy achieved depends on laboratory-measured absorption cross sections and on spectrometer laboratory and field calibration techniques used at each measurement site. The 0.01 DU precision is sufficient to track minute-by-minute changes in C(NO 2 ) throughout each day with typical daytime values ranging from 0.2 to 2 DU. The MFDOAS instrument has better noise characteristics for a single measurement, which permits MFDOAS to operate at higher time resolution than Pandora for the same precision. Because Pandora and MFDOAS direct-sun measurements can be made in the presence of light to moderate clouds, but with reduced precision (~0.2 DU for moderate cloud cover), a nearly continuous record can be obtained, which is important when matching OMI overpass times for satellite data validation. Comparisons between Pandora and MFDOAS with OMI are discussed for the moderately polluted GSFC site, between Pandora and OMI at the AUTH site, and between MFDOAS and OMI at the PNNL site. Validation of OMI measured C(NO 2 ) is essential for the scientific use of the satellite data for air quality, for atmospheric photolysis and chemistry, and for retrieval of other quantities (e.g., accurate atmospheric correction for satellite estimates of ocean reflectance and bio-optical properties). Changes in the diurnal variability of C(NO 2 ) with season and day of the week are presented based on the 2-year time series at GSFC measured by the Pandora instrument.
Nader Abuhassan - One of the best experts on this subject based on the ideXlab platform.
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underestimation of column no 2 amounts from the omi satellite compared to diurnally varying ground based retrievals from multiple Pandora spectrometer instruments
Atmospheric Measurement Techniques, 2019Co-Authors: J R Herman, Nader Abuhassan, Manvendra K Dubey, Marcelo Raponi, Maria TzortziouAbstract:Abstract. Retrievals of total column NO2 ( TCNO2 ) are compared for 14 sites from the Ozone Measuring Instrument (OMI using OMNO2-NASA v3.1) on the AURA satellite and from multiple ground-based Pandora spectrometer instruments making direct-sun measurements. While OMI accurately provides the daily global distribution of retrieved TCNO2 , OMI almost always underestimates the local amount of TCNO2 by 50 % to 100 % in polluted areas, while occasionally the daily OMI value exceeds that measured by Pandora at very clean sites. Compared to local ground-based or aircraft measurements, OMI cannot resolve spatially variable TCNO2 pollution within a city or urban areas, which makes it less suitable for air quality assessments related to human health. In addition to systematic underestimates in polluted areas, OMI's selected 13:30 Equator crossing time polar orbit causes it to miss the frequently much higher values of TCNO2 that occur before or after the OMI overpass time. Six discussed Northern Hemisphere Pandora sites have multi-year data records (Busan, Seoul, Washington DC, Waterflow, New Mexico, Boulder, Colorado, and Mauna Loa), and one site in the Southern Hemisphere (Buenos Aires, Argentina). The first four of these sites and Buenos Aires frequently have high TCNO2 ( TCNO2 > 0.5 DU). Eight additional sites have shorter-term data records in the US and South Korea. One of these is a 1-year data record from a highly polluted site at City College in New York City with pollution levels comparable to Seoul, South Korea. OMI-estimated air mass factor, surface reflectivity, and the OMI 24 km × 13 km FOV (field of view) are three factors that can cause OMI to underestimate TCNO2 . Because of the local inhomogeneity of NOx emissions, the large OMI FOV is the most likely factor for consistent underestimates when comparing OMI TCNO2 to retrievals from the small Pandora effective FOV (measured in m 2) calculated from the solar diameter of 0.5 ∘ .
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spatial and temporal variability of ozone and nitrogen dioxide over a major urban estuarine ecosystem
Journal of Atmospheric Chemistry, 2015Co-Authors: Maria Tzortziou, J R Herman, Alexander Cede, Christopher P Loughner, Nader Abuhassan, Sheenali NaikAbstract:Spatial and temporal dynamics in trace gas pollutants were examined over a major urban estuarine ecosystem, using a new network of ground-based Pandora spectrometers deployed at strategic locations along the Washington-Baltimore corridor and the Chesapeake Bay. Total column ozone (TCO3) and nitrogen dioxide (TCNO2) were measured during NASA’s DISCOVER-AQ and GeoCAPE-CBODAQ campaigns in July 2011. The Pandora network provided high-resolution information on air-quality variability, local pollution conditions, large-scale meteorological influences, and interdependencies of ozone and its major precursor, NO2. Measurements were used to compare with air-quality model simulations (CMAQ), evaluate Aura-OMI satellite retrievals, and assess advantages and limitations of space-based observations under a range of conditions. During the campaign, TCNO2 varied by an order of magnitude, both spatially and temporally. Although fairly constant in rural regions, TCNO2 showed clear diurnal and weekly patterns in polluted urban areas caused by changes in near-surface emissions. With a coarse resolution and an overpass at around 13:30 local time, OMI cannot detect this strong variability in NO2, missing pollution peaks from industrial and rush hour activities. Not as highly variable as NO2, TCO3 was mostly affected by large-scale meteorological patterns as observed by OMI. A clear weekly cycle in TCO3, with minima over the weekend, was due to a combination of weekly weather patterns and changes in near-surface NOx emissions. A Pandora instrument intercomparison under the same conditions at GSFC showed excellent agreement, within ±4.8DU for TCO3 and ±0.07DU for TCNO2 with no air-mass-factor dependence, suggesting that observed variability during the campaign was real.
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comparison of ozone retrievals from the Pandora spectrometer system and dobson spectrophotometer in boulder colorado
Atmospheric Measurement Techniques, 2015Co-Authors: J R Herman, Alexander Cede, Nader Abuhassan, R Evans, Irina Petropavlovskikh, Glen McconvilleAbstract:Abstract. A comparison of retrieved total column ozone (TCO) amounts between the Pandora #34 spectrometer system and the Dobson #061 spectrophotometer from direct-sun observations was performed on the roof of the Boulder, Colorado, NOAA building. This paper, part of an ongoing study, covers a 1-year period starting on 17 December 2013. Both the standard Dobson and Pandora TCO retrievals required a correction, TCOcorr = TCO (1 + C(T)), using a monthly varying effective ozone temperature, TE, derived from a temperature and ozone profile climatology. The correction is used to remove a seasonal difference caused by using a fixed temperature in each retrieval algorithm. The respective corrections C(TE) are CPandora = 0.00333(TE-225) and CDobson = -0.0013(TE-226.7) per degree K. After the applied corrections removed most of the seasonal retrieval dependence on ozone temperature, TCO agreement between the instruments was within 1 % for clear-sky conditions. For clear-sky observations, both co-located instruments tracked the day-to-day variation in total column ozone amounts with a correlation of r2 = 0.97 and an average offset of 1.1 ± 5.8 DU. In addition, the Pandora TCO data showed 0.3 % annual average agreement with satellite overpass data from AURA/OMI (Ozone Monitoring Instrument) and 1 % annual average offset with Suomi-NPP/OMPS (Suomi National Polar-orbiting Partnership, the nadir viewing portion of the Ozone Mapper Profiler Suite).
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high precision absolute total column ozone measurements from the Pandora spectrometer system comparisons with data from a brewer double monochromator and aura omi
Journal of Geophysical Research, 2012Co-Authors: Maria Tzortziou, J R Herman, Alexander Cede, Nader AbuhassanAbstract:We present new, high precision, high temporal resolution measurements of total column ozone (TCO) amounts derived from ground-based direct-sun irradiance measurements using our recently deployed Pandora single-grating spectrometers. Pandora's small size and portability allow deployment at multiple sites within an urban air-shed and development of a ground-based monitoring network for studying small-scale atmospheric dynamics, spatial heterogeneities in trace gas distribution, local pollution conditions, photochemical processes and interdependencies of ozone and its major precursors. Results are shown for four mid- to high-latitude sites where different Pandora instruments were used. Comparisons with a well calibrated double-grating Brewer spectrometer over a period of more than a year in Greenbelt MD showed excellent agreement and a small bias of approximately 2 DU (or, 0.6%). This was constant with slant column ozone amount over the full range of observed solar zenith angles (15-80), indicating adequate Pandora stray light correction. A small (1-2%) seasonal difference was found, consistent with sensitivity studies showing that the Pandora spectral fitting TCO retrieval has a temperature dependence of 1% per 3K, with an underestimation in temperature (e.g., during summer) resulting in an underestimation of TCO. Pandora agreed well with Aura-OMI (Ozone Measuring Instrument) satellite data, with average residuals of <1% at the different sites when the OMI view was within 50 km from the Pandora location and OMI-measured cloud fraction was <0.2. The frequent and continuous measurements by Pandora revealed significant short-term (hourly) temporal changes in TCO, not possible to capture by sun-synchronous satellites, such as OMI, alone.
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no2 column amounts from ground based Pandora and mfdoas spectrometers using the direct sun doas technique intercomparisons and application to omi validation
Journal of Geophysical Research, 2009Co-Authors: J R Herman, Maria Tzortziou, Alexander Cede, E Spinei, G H Mount, Nader AbuhassanAbstract:[1] Vertical column amounts of nitrogen dioxide, C(NO 2 ), are derived from ground-based direct solar irradiance measurements using two new and independently developed spectrometer systems, Pandora (Goddard Space Flight Center) and MFDOAS (Washington State University). We discuss the advantages of C(NO 2 ) retrievals based on Direct Sun - Differential Optical Absorption Spectroscopy (DS-DOAS). The C(NO 2 ) data are presented from field campaigns using Pandora at Aristotle University (AUTH), Thessaloniki, Greece; a second field campaign involving both new instruments at Goddard Space Flight Center (GSFC), Greenbelt, Maryland; a Pandora time series from December 2006 to October 2008 at GSFC; and a MFDOAS time series for spring 2008 at Pacific Northwest National Laboratory (PNNL), Richland, Washington. Pandora and MFDOAS were compared at GFSC and found to closely agree, with both instruments having a clear-sky precision of 0.01 DU (1 DU = 2.67 × 10 16 molecules/cm 2 ) and a nominal accuracy of 0.1 DU. The high precision is obtained from careful laboratory characterization of the spectrometers (temperature sensitivity, slit function, pixel to pixel radiometric calibration, and wavelength calibration), and from sufficient measurement averaging to reduce instrument noise. The accuracy achieved depends on laboratory-measured absorption cross sections and on spectrometer laboratory and field calibration techniques used at each measurement site. The 0.01 DU precision is sufficient to track minute-by-minute changes in C(NO 2 ) throughout each day with typical daytime values ranging from 0.2 to 2 DU. The MFDOAS instrument has better noise characteristics for a single measurement, which permits MFDOAS to operate at higher time resolution than Pandora for the same precision. Because Pandora and MFDOAS direct-sun measurements can be made in the presence of light to moderate clouds, but with reduced precision (~0.2 DU for moderate cloud cover), a nearly continuous record can be obtained, which is important when matching OMI overpass times for satellite data validation. Comparisons between Pandora and MFDOAS with OMI are discussed for the moderately polluted GSFC site, between Pandora and OMI at the AUTH site, and between MFDOAS and OMI at the PNNL site. Validation of OMI measured C(NO 2 ) is essential for the scientific use of the satellite data for air quality, for atmospheric photolysis and chemistry, and for retrieval of other quantities (e.g., accurate atmospheric correction for satellite estimates of ocean reflectance and bio-optical properties). Changes in the diurnal variability of C(NO 2 ) with season and day of the week are presented based on the 2-year time series at GSFC measured by the Pandora instrument.
Alexander Cede - One of the best experts on this subject based on the ideXlab platform.
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assessment of the quality of tropomi high spatial resolution no 2 data products in the greater toronto area
Atmospheric Measurement Techniques, 2020Co-Authors: Xiaoyi Zhao, Alexander Cede, Debora Griffin, Vitali Fioletov, C A Mclinden, Martin Tiefengraber, Moritz Muller, Kristof Bognar, Kimberly Strong, Folkert BoersmaAbstract:Abstract. The TROPOspheric Monitoring Instrument (TROPOMI) aboard the Sentinel-5 Precursor satellite (launched on 13 October 2017) is a nadir-viewing spectrometer measuring reflected sunlight in the ultraviolet, visible, near-infrared, and shortwave infrared spectral ranges. The measured spectra are used to retrieve total columns of trace gases, including nitrogen dioxide ( NO2 ). For ground validation of these satellite measurements, Pandora spectrometers, which retrieve high-quality NO2 total columns via direct-sun measurements, are widely used. In this study, Pandora NO2 measurements made at three sites located in or north of the Greater Toronto Area (GTA) are used to evaluate the TROPOMI NO2 data products, including a standard Royal Netherlands Meteorological Institute (KNMI) tropospheric and stratospheric NO2 data product and a TROPOMI research data product developed by Environment and Climate Change Canada (ECCC) using a high-resolution regional air quality forecast model (in the air mass factor calculation). It is found that these current TROPOMI tropospheric NO2 data products (standard and ECCC) met the TROPOMI design bias requirement (< 10 %). Using the statistical uncertainty estimation method, the estimated TROPOMI upper-limit precision falls below the design requirement at a rural site but above in the other two urban and suburban sites. The Pandora instruments are found to have sufficient precision (< 0.02 DU) to perform TROPOMI validation work. In addition to the traditional satellite validation method (i.e., pairing ground-based measurements with satellite measurements closest in time and space), we analyzed TROPOMI pixels located upwind and downwind from the Pandora site. This makes it possible to improve the statistics and better interpret the high-spatial-resolution measurements made by TROPOMI. By using this wind-based validation technique, the number of coincident measurements can be increased by about a factor of 5. With this larger number of coincident measurements, this work shows that both TROPOMI and Pandora instruments can reveal detailed spatial patterns (i.e., horizontal distributions) of local and transported NO2 emissions, which can be used to evaluate regional air quality changes. The TROPOMI ECCC NO2 research data product shows improved agreement with Pandora measurements compared to the TROPOMI standard tropospheric NO2 data product (e.g., lower multiplicative bias at the suburban and urban sites by about 10 %), demonstrating benefits from the high-resolution regional air quality forecast model.
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spatial and temporal variability of ozone and nitrogen dioxide over a major urban estuarine ecosystem
Journal of Atmospheric Chemistry, 2015Co-Authors: Maria Tzortziou, J R Herman, Alexander Cede, Christopher P Loughner, Nader Abuhassan, Sheenali NaikAbstract:Spatial and temporal dynamics in trace gas pollutants were examined over a major urban estuarine ecosystem, using a new network of ground-based Pandora spectrometers deployed at strategic locations along the Washington-Baltimore corridor and the Chesapeake Bay. Total column ozone (TCO3) and nitrogen dioxide (TCNO2) were measured during NASA’s DISCOVER-AQ and GeoCAPE-CBODAQ campaigns in July 2011. The Pandora network provided high-resolution information on air-quality variability, local pollution conditions, large-scale meteorological influences, and interdependencies of ozone and its major precursor, NO2. Measurements were used to compare with air-quality model simulations (CMAQ), evaluate Aura-OMI satellite retrievals, and assess advantages and limitations of space-based observations under a range of conditions. During the campaign, TCNO2 varied by an order of magnitude, both spatially and temporally. Although fairly constant in rural regions, TCNO2 showed clear diurnal and weekly patterns in polluted urban areas caused by changes in near-surface emissions. With a coarse resolution and an overpass at around 13:30 local time, OMI cannot detect this strong variability in NO2, missing pollution peaks from industrial and rush hour activities. Not as highly variable as NO2, TCO3 was mostly affected by large-scale meteorological patterns as observed by OMI. A clear weekly cycle in TCO3, with minima over the weekend, was due to a combination of weekly weather patterns and changes in near-surface NOx emissions. A Pandora instrument intercomparison under the same conditions at GSFC showed excellent agreement, within ±4.8DU for TCO3 and ±0.07DU for TCNO2 with no air-mass-factor dependence, suggesting that observed variability during the campaign was real.
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comparison of ozone retrievals from the Pandora spectrometer system and dobson spectrophotometer in boulder colorado
Atmospheric Measurement Techniques, 2015Co-Authors: J R Herman, Alexander Cede, Nader Abuhassan, R Evans, Irina Petropavlovskikh, Glen McconvilleAbstract:Abstract. A comparison of retrieved total column ozone (TCO) amounts between the Pandora #34 spectrometer system and the Dobson #061 spectrophotometer from direct-sun observations was performed on the roof of the Boulder, Colorado, NOAA building. This paper, part of an ongoing study, covers a 1-year period starting on 17 December 2013. Both the standard Dobson and Pandora TCO retrievals required a correction, TCOcorr = TCO (1 + C(T)), using a monthly varying effective ozone temperature, TE, derived from a temperature and ozone profile climatology. The correction is used to remove a seasonal difference caused by using a fixed temperature in each retrieval algorithm. The respective corrections C(TE) are CPandora = 0.00333(TE-225) and CDobson = -0.0013(TE-226.7) per degree K. After the applied corrections removed most of the seasonal retrieval dependence on ozone temperature, TCO agreement between the instruments was within 1 % for clear-sky conditions. For clear-sky observations, both co-located instruments tracked the day-to-day variation in total column ozone amounts with a correlation of r2 = 0.97 and an average offset of 1.1 ± 5.8 DU. In addition, the Pandora TCO data showed 0.3 % annual average agreement with satellite overpass data from AURA/OMI (Ozone Monitoring Instrument) and 1 % annual average offset with Suomi-NPP/OMPS (Suomi National Polar-orbiting Partnership, the nadir viewing portion of the Ozone Mapper Profiler Suite).
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high precision absolute total column ozone measurements from the Pandora spectrometer system comparisons with data from a brewer double monochromator and aura omi
Journal of Geophysical Research, 2012Co-Authors: Maria Tzortziou, J R Herman, Alexander Cede, Nader AbuhassanAbstract:We present new, high precision, high temporal resolution measurements of total column ozone (TCO) amounts derived from ground-based direct-sun irradiance measurements using our recently deployed Pandora single-grating spectrometers. Pandora's small size and portability allow deployment at multiple sites within an urban air-shed and development of a ground-based monitoring network for studying small-scale atmospheric dynamics, spatial heterogeneities in trace gas distribution, local pollution conditions, photochemical processes and interdependencies of ozone and its major precursors. Results are shown for four mid- to high-latitude sites where different Pandora instruments were used. Comparisons with a well calibrated double-grating Brewer spectrometer over a period of more than a year in Greenbelt MD showed excellent agreement and a small bias of approximately 2 DU (or, 0.6%). This was constant with slant column ozone amount over the full range of observed solar zenith angles (15-80), indicating adequate Pandora stray light correction. A small (1-2%) seasonal difference was found, consistent with sensitivity studies showing that the Pandora spectral fitting TCO retrieval has a temperature dependence of 1% per 3K, with an underestimation in temperature (e.g., during summer) resulting in an underestimation of TCO. Pandora agreed well with Aura-OMI (Ozone Measuring Instrument) satellite data, with average residuals of <1% at the different sites when the OMI view was within 50 km from the Pandora location and OMI-measured cloud fraction was <0.2. The frequent and continuous measurements by Pandora revealed significant short-term (hourly) temporal changes in TCO, not possible to capture by sun-synchronous satellites, such as OMI, alone.
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no2 column amounts from ground based Pandora and mfdoas spectrometers using the direct sun doas technique intercomparisons and application to omi validation
Journal of Geophysical Research, 2009Co-Authors: J R Herman, Maria Tzortziou, Alexander Cede, E Spinei, G H Mount, Nader AbuhassanAbstract:[1] Vertical column amounts of nitrogen dioxide, C(NO 2 ), are derived from ground-based direct solar irradiance measurements using two new and independently developed spectrometer systems, Pandora (Goddard Space Flight Center) and MFDOAS (Washington State University). We discuss the advantages of C(NO 2 ) retrievals based on Direct Sun - Differential Optical Absorption Spectroscopy (DS-DOAS). The C(NO 2 ) data are presented from field campaigns using Pandora at Aristotle University (AUTH), Thessaloniki, Greece; a second field campaign involving both new instruments at Goddard Space Flight Center (GSFC), Greenbelt, Maryland; a Pandora time series from December 2006 to October 2008 at GSFC; and a MFDOAS time series for spring 2008 at Pacific Northwest National Laboratory (PNNL), Richland, Washington. Pandora and MFDOAS were compared at GFSC and found to closely agree, with both instruments having a clear-sky precision of 0.01 DU (1 DU = 2.67 × 10 16 molecules/cm 2 ) and a nominal accuracy of 0.1 DU. The high precision is obtained from careful laboratory characterization of the spectrometers (temperature sensitivity, slit function, pixel to pixel radiometric calibration, and wavelength calibration), and from sufficient measurement averaging to reduce instrument noise. The accuracy achieved depends on laboratory-measured absorption cross sections and on spectrometer laboratory and field calibration techniques used at each measurement site. The 0.01 DU precision is sufficient to track minute-by-minute changes in C(NO 2 ) throughout each day with typical daytime values ranging from 0.2 to 2 DU. The MFDOAS instrument has better noise characteristics for a single measurement, which permits MFDOAS to operate at higher time resolution than Pandora for the same precision. Because Pandora and MFDOAS direct-sun measurements can be made in the presence of light to moderate clouds, but with reduced precision (~0.2 DU for moderate cloud cover), a nearly continuous record can be obtained, which is important when matching OMI overpass times for satellite data validation. Comparisons between Pandora and MFDOAS with OMI are discussed for the moderately polluted GSFC site, between Pandora and OMI at the AUTH site, and between MFDOAS and OMI at the PNNL site. Validation of OMI measured C(NO 2 ) is essential for the scientific use of the satellite data for air quality, for atmospheric photolysis and chemistry, and for retrieval of other quantities (e.g., accurate atmospheric correction for satellite estimates of ocean reflectance and bio-optical properties). Changes in the diurnal variability of C(NO 2 ) with season and day of the week are presented based on the 2-year time series at GSFC measured by the Pandora instrument.
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the Pandora software development kit for pattern recognition
European Physical Journal C, 2015Co-Authors: J Marshall, M ThomsonAbstract:The development of automated solutions to pattern recognition problems is important in many areas of scientific research and human endeavour. This paper describes the implementation of the Pandora software development kit, which aids the process of designing, implementing and running pattern recognition algorithms. The Pandora Application Programming Interfaces ensure simple specification of the building-blocks defining a pattern recognition problem. The logic required to solve the problem is implemented in algorithms. The algorithms request operations to create or modify data structures and the operations are performed by the Pandora framework. This design promotes an approach using many decoupled algorithms, each addressing specific topologies. Details of algorithms addressing two pattern recognition problems in High Energy Physics are presented: reconstruction of events at a high-energy \(e^{+}e^{-}\) linear collider and reconstruction of cosmic ray or neutrino events in a liquid argon time projection chamber.
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The Pandora Software Development Kit for Pattern Recognition
The European Physical Journal C, 2015Co-Authors: J Marshall, M. A. ThomsonAbstract:The development of automated solutions to pattern recognition problems is important in many areas of scientific research and human endeavour. This paper describes the implementation of the Pandora Software Development Kit, which aids the process of designing, implementing and running pattern recognition algorithms. The Pandora Application Programming Interfaces ensure simple specification of the building-blocks defining a pattern recognition problem. The logic required to solve the problem is implemented in algorithms. The algorithms request operations to create or modify data structures and the operations are performed by the Pandora framework. This design promotes an approach using many decoupled algorithms, each addressing specific topologies. Details of algorithms addressing two pattern recognition problems in High Energy Physics are presented: reconstruction of events at a high-energy e+e- linear collider and reconstruction of cosmic ray or neutrino events in a liquid argon time projection chamber.
