scholarly journals The Berkeley High Resolution Tropospheric NO<sub>2</sub> product

2018 ◽  
Vol 10 (4) ◽  
pp. 2069-2095 ◽  
Author(s):  
Joshua L. Laughner ◽  
Qindan Zhu ◽  
Ronald C. Cohen
Keyword(s):  
High Resolution ◽  
A Priori ◽  
Retrieval Algorithm ◽  
Ozone Monitoring Instrument ◽  
Pixel Resolution ◽  
Vertical Column ◽  
Factors Affecting ◽  
Lower Canada ◽  
The University ◽  
The Impact

Abstract. We describe upgrades to the Berkeley High Resolution (BEHR) NO2 satellite retrieval product. BEHR v3.0B builds on the NASA version 3 standard Ozone Monitoring Instrument (OMI) tropospheric NO2 product to provide a high spatial resolution product for a domain covering the continental United States and lower Canada that is consistent with daily variations in the 12 km a priori NO2 profiles. Other improvements to the BEHR v3.0 product include surface reflectance and elevation, and factors affecting the NO2 a priori profiles such as lightning and anthropogenic emissions.We describe the retrieval algorithm in detail and evaluate the impact of changes to the algorithm between v2.1C and v3.0B on the retrieved NO2 vertical column densities (VCDs). Not surprisingly, we find that, on average, the changes to the a priori NO2 profiles and the update to the new NASA slant column densities have the greatest impact on the retrieved VCDs. More significantly, we find that using daily a priori profiles results in greater average VCDs than using monthly profiles in regions and times with significant lightning activity.The BEHR product is available as four subproducts on the University of California DASH repository, using monthly a priori profiles at native OMI pixel resolution (https://doi.org/10.6078/D1N086) and regridded to 0.05° × 0.05° (https://doi.org/10.6078/D1RQ3G) and using daily a priori profiles at native OMI (https://doi.org/10.6078/D1WH41) and regridded (https://doi.org/10.6078/D12D5X) resolutions. The subproducts using monthly profiles are currently available from January 2005 to July 2017, and will be expanded to more recent years. The subproducts using daily profiles are currently available for years 2005–2010 and 2012–2014; 2011 and 2015 on will be added as the necessary input data are simulated for those years.

scholarly journals The Berkeley High Resolution Tropospheric NO<sub>2</sub> Product

2018 ◽  
Author(s):  
Joshua L. Laughner ◽  
Qindan Zhu ◽  
Ronald C. Cohen
Keyword(s):  
High Resolution ◽  
A Priori ◽  
Retrieval Algorithm ◽  
Ozone Monitoring Instrument ◽  
Pixel Resolution ◽  
Vertical Column ◽  
Factors Affecting ◽  
Satellite Retrieval ◽  
The University ◽  
The Impact

Abstract. We describe upgrades to the Berkeley High Resolution (BEHR) NO2 satellite retrieval product. BEHR v3.0 builds on the NASA version 3 standard Ozone Monitoring Instrument (OMI) tropospheric NO2 product to provide a high spatial resolution product that is consistent with daily variations in the 12 km a priori NO2 profiles. Other improvements to the BEHR v3.0 product include surface reflectance and elevation, and factors affecting the NO2 a priori profiles such as lightning and anthropogenic emissions. We describe the retrieval algorithm in detail and evaluate the impact of changes to the algorithm between v2.1C and v3.0B has on the retrieved NO2 vertical column densities (VCDs). Not surprisingly, we find that, on average, the changes to the a priori NO2 profiles and the update to the new NASA slant column densities have the greatest impact on the retrieved VCDs. More significantly, we find that using daily a priori profiles results in greater average VCDs than using monthly profiles in regions and times with significant lightning activity. The BEHR product is available as four subproducts on the University of California DASH repository: using monthly a priori profiles at native OMI pixel resolution (https://doi.org/10.6078/D1N086) and regridded to 0.05° × 0.05° (https://doi.org/10.6078/D1RQ3G) and using daily a priori profiles at native OMI ( https://doi.org/10.6078/D1WH41) and regridded (https: //doi.org/10.6078/D12D5X) resolutions.

scholarly journals Satellite constraint for emissions of nitrogen oxides from anthropogenic, lightning and soil sources over East China on a high-resolution grid

2011 ◽  
Vol 11 (11) ◽  
pp. 29807-29843 ◽  
Author(s):  
J.-T. Lin
Keyword(s):  
High Resolution ◽  
Nitrogen Oxides ◽  
A Priori ◽  
East China ◽  
Anthropogenic Emissions ◽  
Ozone Monitoring Instrument ◽  
Vertical Column ◽  
The North ◽  
Sensitivity Tests ◽  
Soil Emissions

Abstract. Vertical column densities (VCDs) of tropospheric nitrogen dioxide (NO2) retrieved from space provide valuable information to estimate emissions of nitrogen oxides (NOx) inversely. Accurate emission attribution to individual sources, important both for understanding the global biogeochemical cycling of nitrogen and for emission control, remains difficult. This study presents a regression-based multi-step inversion approach to estimate emissions of NOx from anthropogenic, lightning and soil sources individually for 2006 over East China on a 0.25° long × 0.25° lat grid, employing the DOMINO product version 2 retrieved from the Ozone Monitoring Instrument. The nested GEOS-Chem model for East Asia is used to simulate the seasonal variations of different emission sources and impacts on VCDs of NO2 for the inversion purpose. Sensitivity tests are conducted to evaluate key assumptions embedded in the inversion process. The inverse estimate suggests annual budgets of about 7.1 TgN (±38%), 0.22 TgN (±46%), and 0.40 TgN (±48%) for the a posteriori anthropogenic, lightning and soil emissions, respectively, each about 24% higher than the respective a priori values. The enhancements in anthropogenic emissions are largest in cities and areas with extensive use of coal, particularly in the north in winter, as evident on the high-resolution grid. Derived soil emissions are consistent with recent bottom-up estimates. They are each less than 6% of anthropogenic emissions annually, increasing to about 13% for July. Overall, anthropogenic emissions are found to be the dominant source of NOx over East China with important implications for nitrogen control.

scholarly journals Evaluating the impact of spatial resolution on tropospheric NO<sub>2</sub> column comparisons within urban areas using high-resolution airborne data

2019 ◽  
Vol 12 (11) ◽  
pp. 6091-6111 ◽  
Author(s):  
Laura M. Judd ◽  
Jassim A. Al-Saadi ◽  
Scott J. Janz ◽  
Matthew G. Kowalewski ◽  
R. Bradley Pierce ◽  
...  
Keyword(s):  
High Resolution ◽  
Los Angeles ◽  
Spatial Heterogeneity ◽  
Spatial Resolution ◽  
Urban Areas ◽  
High Temporal Resolution ◽  
Ozone Monitoring Instrument ◽  
Vertical Column ◽  
Monitoring Instrument ◽  
The Impact

Abstract. NASA deployed the GeoTASO airborne UV–visible spectrometer in May–June 2017 to produce high-resolution (approximately 250 m×250 m) gapless NO2 datasets over the western shore of Lake Michigan and over the Los Angeles Basin. The results collected show that the airborne tropospheric vertical column retrievals compare well with ground-based Pandora spectrometer column NO2 observations (r2=0.91 and slope of 1.03). Apparent disagreements between the two measurements can be sensitive to the coincidence criteria and are often associated with large local variability, including rapid temporal changes and spatial heterogeneity that may be observed differently by the sunward-viewing Pandora observations. The gapless mapping strategy executed during the 2017 GeoTASO flights provides data suitable for averaging to coarser areal resolutions to simulate satellite retrievals. As simulated satellite pixel area increases to values typical of TEMPO (Tropospheric Emissions: Monitoring Pollution), TROPOMI (TROPOspheric Monitoring Instrument), and OMI (Ozone Monitoring Instrument), the agreement with Pandora measurements degraded, particularly for the most polluted columns as localized large pollution enhancements observed by Pandora and GeoTASO are spatially averaged with nearby less-polluted locations within the larger area representative of the satellite spatial resolutions (aircraft-to-Pandora slope: TEMPO scale =0.88; TROPOMI scale =0.77; OMI scale =0.57). In these two regions, Pandora and TEMPO or TROPOMI have the potential to compare well at least up to pollution scales of 30×1015 molecules cm−2. Two publicly available OMI tropospheric NO2 retrievals are found to be biased low with respect to these Pandora observations. However, the agreement improves when higher-resolution a priori inputs are used for the tropospheric air mass factor calculation (NASA V3 standard product slope =0.18 and Berkeley High Resolution product slope =0.30). Overall, this work explores best practices for satellite validation strategies with Pandora direct-sun observations by showing the sensitivity to product spatial resolution and demonstrating how the high-spatial-resolution NO2 data retrieved from airborne spectrometers, such as GeoTASO, can be used with high-temporal-resolution ground-based column observations to evaluate the influence of spatial heterogeneity on validation results.

scholarly journals An improved tropospheric NO<sub>2</sub> column retrieval algorithm for the Ozone Monitoring Instrument

2011 ◽  
Vol 4 (9) ◽  
pp. 1905-1928 ◽  
Author(s):  
K. F. Boersma ◽  
H. J. Eskes ◽  
R. J. Dirksen ◽  
R. J. van der A ◽  
J. P. Veefkind ◽  
...  
Keyword(s):  
High Resolution ◽  
Surface Albedo ◽  
Retrieval Algorithm ◽  
Ozone Monitoring Instrument ◽  
Air Mass ◽  
Monitoring Instrument ◽  
Tropospheric No2 ◽  
Mass Factor ◽  
Ozone Monitoring ◽  
The Impact

Abstract. We present an improved tropospheric nitrogen dioxide column retrieval algorithm (DOMINO v2.0) for OMI based on better air mass factors (AMFs) and a correction for across-track stripes resulting from calibration errors in the OMI backscattered reflectances. Since October 2004, NO2 retrievals from the Ozone Monitoring Instrument (OMI), a UV/Vis nadir spectrometer onboard NASA's EOS-Aura satellite, have been used with success in several scientific studies focusing on air quality monitoring, detection of trends, and NOx emission estimates. Dedicated evaluations of previous DOMINO tropospheric NO2 retrievals indicated their good quality, but also suggested that the tropospheric columns were susceptible to high biases (by 0–40%), probably because of errors in the air mass factor calculations. Here we update the DOMINO air mass factor approach. We calculate a new look-up table (LUT) for altitude-dependent AMFs based on more realistic atmospheric profile parameters, and include more surface albedo and surface pressure reference points than before. We improve the sampling of the TM4 model, resulting in a priori NO2 profiles that are better mixed throughout the boundary layer. We evaluate the NO2 profiles simulated with the improved TM4 sampling as used in the AMF calculations and show that they are highly consistent with in situ NO2 measurements from aircraft during the INTEX-A and INTEX-B campaigns in 2004 and 2006. Our air mass factor calculations are further updated by the implementation of a high-resolution terrain height and a high-resolution surface albedo climatology based on OMI measurements. Together with a correction for across-track stripes, the overall impact of the improved terrain height and albedo descriptions is modest (<5%) on average over large polluted areas, but still causes significant changes locally. The main changes in the DOMINO v2.0 algorithm follow from the new LUT and the improved TM4 sampling that results in more NO2 simulated aloft, where sensitivity to NO2 is higher, and amount to reductions in tropospheric NO2 columns of up to 20% in winter, and 10% in summer over extended polluted areas. We investigate the impact of aerosols on the NO2 retrieval, and based on a comparison of concurrent retrievals of clouds from OMI and aerosols from MODIS Aqua, we find empirical evidence that OMI cloud retrievals are sensitive to the presence of scattering aerosols. It follows that an implicit correction for the effects of aerosols occurs through the aerosol-induced cloud parameters in DOMINO, and we show that such an empirical correction amounts to a 20 %AMF reduction in summer and ±10% changes in winter over the eastern United States.

Assessment of the S-5P tropospheric NO2 product based on coincident airborne APEX observations over polluted regions

2020 ◽  
Author(s):  
Frederik Tack ◽  
Alexis Merlaud ◽  
Marian-Daniel Iordache ◽  
Gaia Pinardi ◽  
Ermioni Dimitropoulou ◽  
...  
Keyword(s):  
High Resolution ◽  
A Priori ◽  
Horizontal Distribution ◽  
Time Interval ◽  
Short Time Interval ◽  
Vertical Column ◽  
Urban Regions ◽  
Accuracy Requirement ◽  
Spatio Temporal ◽  
The Impact

&lt;p&gt;Sentinel-5 Precursor (S-5P), launched in October 2017, is the first mission of the Copernicus Programme dedicated to the monitoring of air quality and climate. Its characteristics, such as the fine spatial resolution, introduce many new opportunities and challenges, requiring to carefully assess the quality and validity of the generated data products by comparison with independent reference observations.&lt;/p&gt;&lt;p&gt;In the presented study, the S-5P/TROPOMI tropospheric nitrogen dioxide (NO&lt;sub&gt;2&lt;/sub&gt;) L2 product (3.5 x 7 km&lt;sup&gt;2 &lt;/sup&gt;at nadir observations) has been validated over strongly polluted urban regions based on comparison with coincident high-resolution airborne remote sensing observations (~100 m&lt;sup&gt;2&lt;/sup&gt;). Airborne imagers are able to map the horizontal distribution of tropospheric NO&lt;sub&gt;2&lt;/sub&gt;, as well as its strong spatio-temporal variability, at high resolution and with high accuracy. Satellite products can be optimally assessed based on airborne observations as a large amount of satellite pixels can be fully mapped in a relatively short time interval, reducing the impact of spatiotemporal mismatches. Additionally, such data sets allow to study the TROPOMI subpixel variability and impact of signal smoothing due to its finite satellite pixel size, typically coarser than fine-scale gradients in the urban NO&lt;sub&gt;2&lt;/sub&gt; field.&lt;/p&gt;&lt;p&gt;In the framework of the S5PVAL-BE campaign, the Airborne Prism EXperiment (APEX) imaging spectrometer has been deployed during four mapping flights (26-29 June 2019) over the two largest urban regions in Belgium, i.e. Brussels and Antwerp, in order to map the horizontal distribution of tropospheric NO&lt;sub&gt;2&lt;/sub&gt;. Per flight, 15 to 20 TROPOMI pixels were fully covered by approximately 5000 APEX measurements for each TROPOMI pixel. Mapping flights and ancillary ground-based measurements (car-mobile DOAS, MAX-DOAS, CIMEL, ceilometer, etc.) were conducted in coincidence with the overpass of TROPOMI (typically between noon and 2 PM UTC). The TROPOMI and APEX NO&lt;sub&gt;2&lt;/sub&gt; vertical column density (VCD) retrieval schemes are similar in concept. Retrieved NO&lt;sub&gt;2 &lt;/sub&gt;VCDs were georeferenced, gridded and intercompared. As strongly polluted areas typically exhibit strong NO&lt;sub&gt;2 &lt;/sub&gt;vertical gradients (besides the strong horizontal gradients), a custom TROPOMI tropospheric NO&lt;sub&gt;2 &lt;/sub&gt;product was computed and compared as well with APEX by replacing the coarse 1&amp;#176; x 1&amp;#176; a priori NO&lt;sub&gt;2 &lt;/sub&gt;vertical profiles from TM5-MP by NO&lt;sub&gt;2&lt;/sub&gt; profile shapes from the CAMS regional CTM ensemble at 0.1&amp;#176; x 0.1&amp;#176;.&lt;/p&gt;&lt;p&gt;Overall for the ensemble of the four flights, the standard TROPOMI NO&lt;sub&gt;2&lt;/sub&gt; VCD product is well correlated (R= 0.94) but biased low (slope = 0.73) with respect to APEX NO&lt;sub&gt;2&lt;/sub&gt; retrievals. When replacing the TM5-MP a priori NO&lt;sub&gt;2&lt;/sub&gt; profiles by CAMS-based profiles, the slope increases to 0.88. When calculating the NO&lt;sub&gt;2&lt;/sub&gt; VCD differences, the bias is on average -1.3 &amp;#177; 1.2 x 10&lt;sup&gt;15&lt;/sup&gt; molec cm&lt;sup&gt;-2&lt;/sup&gt; or -16% &amp;#177; 11% for the difference between APEX NO&lt;sub&gt;2&lt;/sub&gt; VCDs and the standard TROPOMI NO&lt;sub&gt;2&lt;/sub&gt; VCD product. The bias is substantially reduced when replacing the coarse TM5-MP a priori NO&lt;sub&gt;2&lt;/sub&gt; profiles by CAMS-based profiles, being -0.1 &amp;#177; 1.1&amp;#160; x 10&lt;sup&gt;15&lt;/sup&gt; molec cm&lt;sup&gt;-2&lt;/sup&gt; or -0.1% &amp;#177; 11%. Both sets of retrievals are well within the accuracy requirement of a maximum bias of 25-50% for the TROPOMI tropospheric NO&lt;sub&gt;2&lt;/sub&gt; product for all individual compared pixels.&lt;/p&gt;

scholarly journals Evaluating the impact of spatial resolution on tropospheric NO<sub>2</sub> column comparisons within urban areas using high-resolution airborne data

2019 ◽  
Author(s):  
Laura M. Judd ◽  
Jassim A. Al-Saadi ◽  
Scott J. Janz ◽  
Matthew G. Kowalewski ◽  
R. Bradley Pierce ◽  
...  
Keyword(s):  
High Resolution ◽  
Los Angeles ◽  
Spatial Heterogeneity ◽  
Spatial Resolution ◽  
Urban Areas ◽  
Lake Michigan ◽  
A Priori ◽  
High Temporal Resolution ◽  
Vertical Column ◽  
The Impact

Abstract. NASA deployed an airborne UV/Visible spectrometer, GeoTASO, in May–June 2017 to produce high resolution (approximately 250 × 250 m), gapless NO2 datasets over the western shore of Lake Michigan and over the Los Angeles Basin. Results show that the airborne tropospheric vertical column retrievals compare well with ground-based Pandora spectrometer column NO2 observations (r2 = 0.91 and slope of 1.03). Apparent disagreements between the two measurements can be sensitive to the coincidence criteria and are often associated with large local variability, including rapid temporal changes and also spatial heterogeneity that may be observed differently by the sunward viewing Pandora observations. The gapless mapping strategy executed during the 2017 GeoTASO flights provides data suitable for averaging to coarser areal resolutions to simulate satellite retrievals. As simulated satellite pixel area increases to values typical of TEMPO, TROPOMI, and OMI, the agreement with Pandora measurements is degraded as localized polluted plumes observed by Pandora are spatially averaged over larger areas (aircraft-to-Pandora slope: TEMPO scale = 0.88; TROPOMI scale = 0.77; OMI scale = 0.57). This behavior suggests that satellite products are representative of individual Pandora observations up to a certain pollution scale that depends on satellite spatial resolution. In these two regions, Pandora and TEMPO or TROPOMI have the potential to compare well up to pollution scales of 30 x 1015 molecules cm−2. Two publicly available OMI tropospheric NO2 retrievals are both found to be biased low with respect to Pandora observations (NASA V3 Standard Product slope = 0.18 and Berkeley High Resolution Product slope = 0.30). However, the agreement improves when higher resolution a priori inputs are used for the tropospheric air mass factor calculation. Overall, this work explores best practices for satellite validation strategies by showing the sensitivity to product spatial resolution and demonstrates how the high spatial resolution NO2 data retrieved from airborne spectrometers, such as GeoTASO, can be used with high temporal resolution surface observations to evaluate the influence of spatial heterogeneity on validation results.

scholarly journals Satellite constraint for emissions of nitrogen oxides from anthropogenic, lightning and soil sources over East China on a high-resolution grid

2012 ◽  
Vol 12 (6) ◽  
pp. 2881-2898 ◽  
Author(s):  
J.-T. Lin
Keyword(s):  
High Resolution ◽  
Nitrogen Oxides ◽  
A Priori ◽  
East China ◽  
Anthropogenic Emissions ◽  
Ozone Monitoring Instrument ◽  
Vertical Column ◽  
The North ◽  
Sensitivity Tests ◽  
Soil Emissions

Abstract. Vertical column densities (VCDs) of tropospheric nitrogen dioxide (NO2) retrieved from space provide valuable information to estimate emissions of nitrogen oxides (NOx) inversely. Accurate emission attribution to individual sources, important both for understanding the global biogeochemical cycling of nitrogen and for emission control, remains difficult. This study presents a regression-based multi-step inversion approach to estimate emissions of NOx from anthropogenic, lightning and soil sources individually for 2006 over East China on a 0.25° long × 0.25° lat grid, employing the DOMINO product version 2 retrieved from the Ozone Monitoring Instrument. The inversion is done gridbox by gridbox to derive the respective emissions, taking advantage of differences in seasonality between anthropogenic and natural sources. Lightning and soil emissions are combined together for any given gridbox due to their similar seasonality; and their different spatial distributions are used implicitly for source separation to some extent. The nested GEOS-Chem model for East Asia is used to simulate the seasonal variations of different emission sources and impacts on VCDs of NO2 for the inversion purpose. Sensitivity tests are conducted to evaluate key assumptions embedded in the inversion process. The inverse estimate suggests annual budgets of about 7.1 TgN (±39%), 0.21 TgN (±61%), and 0.38 TgN (±65%) for the a posteriori anthropogenic, lightning and soil emissions, respectively, about 18–23% higher than the respective a priori values. The enhancements in anthropogenic emissions are largest in cities and areas with extensive use of coal, particularly in the north in winter, as evident on the high-resolution grid. Derived soil emissions are consistent with recent bottom-up estimates. They are less than 6% of anthropogenic emissions annually, increasing to about 13% for July. Derived lightning emissions are about 3% of anthropogenic emissions annually and about 10% in July. Overall, anthropogenic emissions are found to be the dominant source of NOx over East China with important implications for nitrogen control.

scholarly journals The high-resolution version of TM5-MP for optimized satellite retrievals: description and validation

2017 ◽  
Vol 10 (2) ◽  
pp. 721-750 ◽  
Author(s):  
Jason E. Williams ◽  
K. Folkert Boersma ◽  
Phillipe Le Sager ◽  
Willem W. Verstraeten
Keyword(s):  
High Resolution ◽  
Vertical Distribution ◽  
Transport Model ◽  
Meteorological Data ◽  
Ozone Monitoring Instrument ◽  
Vertical Column ◽  
Monitoring Instrument ◽  
Satellite Retrievals ◽  
The Impact ◽  
Lightning Nox

Abstract. We provide a comprehensive description of the high-resolution version of the TM5-MP global chemistry transport model, which is to be employed for deriving highly resolved vertical profiles of nitrogen dioxide (NO2), formaldehyde (CH2O), and sulfur dioxide (SO2) for use in satellite retrievals from platforms such as the Ozone Monitoring Instrument (OMI) and the Sentinel-5 Precursor, and the TROPOspheric Monitoring Instrument (tropOMI). Comparing simulations conducted at horizontal resolutions of 3°  ×  2° and 1°  ×  1° reveals differences of ±20 % exist in the global seasonal distribution of 222Rn, being larger near specific coastal locations and tropical oceans. For tropospheric ozone (O3), analysis of the chemical budget terms shows that the impact on globally integrated photolysis rates is rather low, in spite of the higher spatial variability of meteorological data fields from ERA-Interim at 1°  ×  1°. Surface concentrations of O3 in high-NOx regions decrease between 5 and 10 % at 1°  ×  1° due to a reduction in NOx recycling terms and an increase in the associated titration term of O3 by NO. At 1°  ×  1°, the net global stratosphere–troposphere exchange of O3 decreases by  ∼  7 %, with an associated shift in the hemispheric gradient. By comparing NO, NO2, HNO3 and peroxy-acetyl-nitrate (PAN) profiles against measurement composites, we show that TM5-MP captures the vertical distribution of NOx and long-lived NOx reservoirs at background locations, again with modest changes at 1°  ×  1°. Comparing monthly mean distributions in lightning NOx and applying ERA-Interim convective mass fluxes, we show that the vertical re-distribution of lightning NOx changes with enhanced release of NOx in the upper troposphere. We show that surface mixing ratios in both NO and NO2 are generally underestimated in both low- and high-NOx scenarios. For Europe, a negative bias exists for [NO] at the surface across the whole domain, with lower biases at 1°  ×  1° at only  ∼  20 % of sites. For NO2, biases are more variable, with lower (higher) biases at 1°  ×  1° occurring at  ∼  35 % ( ∼  20 %) of sites, with the remainder showing little change. For CH2O, the impact of higher resolution on the chemical budget terms is rather modest, with changes of less than 5 %. The simulated vertical distribution of CH2O agrees reasonably well with measurements in pristine locations, although column-integrated values are generally underestimated relative to satellite measurements in polluted regions. For SO2, the performance at 1°  ×  1° is principally governed by the quality of the emission inventory, with limited improvements in the site-specific biases, with most showing no significant improvement. For the vertical column, improvements near strong source regions occur which reduce the biases in the integrated column. For remote regions missing biogenic source terms are inferred.

scholarly journals An improved tropospheric NO<sub>2</sub> column retrieval algorithm for the Ozone Monitoring Instrument

2011 ◽  
Vol 4 (2) ◽  
pp. 2329-2388 ◽  
Author(s):  
K. F. Boersma ◽  
H. J. Eskes ◽  
R. J. Dirksen ◽  
R. J. van der A ◽  
J. P. Veefkind ◽  
...  
Keyword(s):  
High Resolution ◽  
Surface Albedo ◽  
Retrieval Algorithm ◽  
Ozone Monitoring Instrument ◽  
Air Mass ◽  
Monitoring Instrument ◽  
Tropospheric No2 ◽  
Mass Factor ◽  
Ozone Monitoring ◽  
The Impact

Abstract. We present an improved tropospheric nitrogen dioxide column retrieval algorithm (DOMINO v2.0) for OMI based on better air mass factors (AMFs) and a correction for across-track stripes resulting from calibration errors in the OMI backscattered reflectances. Since October 2004, NO2 retrievals from the Ozone Monitoring Instrument (OMI), a UV/Vis nadir spectrometer onboard NASA's EOS-Aura satellite, have been used with success in several scientific studies focusing on air quality monitoring, detection of trends, and NOx emission estimates. Dedicated evaluations of previous DOMINO tropospheric NO2 retrievals indicated their good quality, but also suggested that the tropospheric columns were susceptible to high biases (by 0–40%), probably because of errors in the air mass factor calculations. Here we update the DOMINO air mass factor approach. We calculate a new look-up table (LUT) for altitude-dependent AMFs based on more realistic atmospheric profile parameters, and include more surface albedo and surface pressure reference points than before. We improve the sampling of the TM4 model, resulting in a priori NO2 profiles that are better mixed throughout the boundary layer. We evaluate the NO2 profiles simulated with the improved TM4 sampling as used in the AMF calculations and show that they are highly consistent with in situ NO2 measurements from aircraft during the INTEX-A and INTEX-B campaigns in 2004 and 2006. Our air mass factor calculations are further updated by the implementation of a high-resolution terrain height and a high-resolution surface albedo climatology based on OMI measurements. Together with a correction for across-track stripes, the overall impact of the improved terrain height and albedo descriptions is modest (<5%) on average over large polluted areas, but still causes significant changes locally. The main changes in the DOMINO v2.0 algorithm follow from the new LUT and the improved TM4 sampling that results in more NO2 simulated aloft, where sensitivity to NO2 is higher, and amount to reductions in tropospheric NO2 columns of up to 20% in winter, and 10% in summer over extended polluted areas. We investigate the impact of aerosols on the NO2 retrieval, and based on a comparison of concurrent retrievals of clouds from OMI and aerosols from MODIS Aqua, we find empirical evidence that OMI cloud retrievals are sensitive to the presence of scattering aerosols. It follows that an implicit correction for the effects of aerosols occurs through the aerosol-induced cloud parameters in DOMINO, and we show that such a correction amounts to a 20% AMF reduction in summer and ±10% changes in winter over the eastern US.

Structural Model of Service Quality Factors Affecting Loyalty Sustainability

2020 ◽  
Vol 11 (2) ◽  
Author(s):  
Eman Al-erqi ◽  
◽  
Mohd Lizam Mohd Diah ◽  
Najmaddin Abo Mosali ◽  
◽  
...  
Keyword(s):  
International Students ◽  
Service Quality ◽  
Goodness Of Fit ◽  
Structural Model ◽  
Quality Factors ◽  
Factors Affecting ◽  
Measurement Models ◽  
Confirmatory Factor ◽  
The University ◽  
The Impact

This study seeks to address the impact of service quality affecting international student's satisfaction towards loyalty tothe Universiti Tun Hussein Onn Malaysia(UTHM). The aim of thestudy is to develop relationship between service quality factor and loyalty to the university from the international students’ perspectives. The study adopted quantitative approach where data was collected through questionnaire survey and analysed statistically. A total of 246 responses were received and found to be valid. The model was developed and analysed using AMOS-SEM software. Confirmatory factor analysis (CFA) function of the software was to assessed the measurement models and found that all the models achieved goodness of fit. Then path analysis function was used to assessed structural model and found that service qualityfactors have a significant effect on the students’ satisfaction and thus affecting the loyaltyto the university. Hopefully the outcome form this study will benefit the university in providing services especially to the international students.

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