scholarly journals Comparative assessment of TROPOMI and OMI formaldehyde observations and validation against MAX-DOAS network column measurements

2021 ◽  
Vol 21 (16) ◽  
pp. 12561-12593
Author(s):  
Isabelle De Smedt ◽  
Gaia Pinardi ◽  
Corinne Vigouroux ◽  
Steven Compernolle ◽  
Alkis Bais ◽  
...  
Keyword(s):  
Horizontal Resolution ◽  
Global Network ◽  
Optical Absorption Spectroscopy ◽  
Positive Bias ◽  
Ozone Monitoring Instrument ◽  
Temporal Scales ◽  
Tropical Regions ◽  
Spatial And Temporal Scales ◽  
Monitoring Instrument ◽  
Combined Time Series

Abstract. The TROPOspheric Monitoring Instrument (TROPOMI), launched in October 2017 on board the Sentinel-5 Precursor (S5P) satellite, monitors the composition of the Earth's atmosphere at an unprecedented horizontal resolution as fine as 3.5 × 5.5 km2. This paper assesses the performances of the TROPOMI formaldehyde (HCHO) operational product compared to its predecessor, the OMI (Ozone Monitoring Instrument) HCHO QA4ECV product, at different spatial and temporal scales. The parallel development of the two algorithms favoured the consistency of the products, which facilitates the production of long-term combined time series. The main difference between the two satellite products is related to the use of different cloud algorithms, leading to a positive bias of OMI compared to TROPOMI of up to 30 % in tropical regions. We show that after switching off the explicit correction for cloud effects, the two datasets come into an excellent agreement. For medium to large HCHO vertical columns (larger than 5 × 1015 molec. cm−2) the median bias between OMI and TROPOMI HCHO columns is not larger than 10 % (< 0.4 × 1015 molec. cm−2). For lower columns, OMI observations present a remaining positive bias of about 20 % (< 0.8 × 1015 molec. cm−2) compared to TROPOMI in midlatitude regions. Here, we also use a global network of 18 MAX-DOAS (multi-axis differential optical absorption spectroscopy) instruments to validate both satellite sensors for a large range of HCHO columns. This work complements the study by Vigouroux et al. (2020), where a global FTIR (Fourier transform infrared) network is used to validate the TROPOMI HCHO operational product. Consistent with the FTIR validation study, we find that for elevated HCHO columns, TROPOMI data are systematically low (−25 % for HCHO columns larger than 8 × 1015 molec. cm−2), while no significant bias is found for medium-range column values. We further show that OMI and TROPOMI data present equivalent biases for large HCHO levels. However, TROPOMI significantly improves the precision of the HCHO observations at short temporal scales and for low HCHO columns. We show that compared to OMI, the precision of the TROPOMI HCHO columns is improved by 25 % for individual pixels and by up to a factor of 3 when considering daily averages in 20 km radius circles. The validation precision obtained with daily TROPOMI observations is comparable to the one obtained with monthly OMI observations. To illustrate the improved performances of TROPOMI in capturing weak HCHO signals, we present clear detection of HCHO column enhancements related to shipping emissions in the Indian Ocean. This is achieved by averaging data over a much shorter period (3 months) than required with previous sensors (5 years) and opens new perspectives to study shipping emissions of VOCs (volatile organic compounds) and related atmospheric chemical interactions.

scholarly journals Comparative assessment of TROPOMI and OMI formaldehyde observations against MAX-DOAS network column measurements

2021 ◽  
Author(s):  
Isabelle De Smedt ◽  
Gaia Pinardi ◽  
Corinne Vigouroux ◽  
Steven Compernolle ◽  
Alkis Bais ◽  
...  
Keyword(s):  
Horizontal Resolution ◽  
Global Network ◽  
Positive Bias ◽  
Temporal Scales ◽  
Tropical Regions ◽  
Spatial And Temporal Scales ◽  
Satellite Sensors ◽  
The Indian Ocean ◽  
The One ◽  
Combined Time Series

Abstract. The TROPOspheric Monitoring Instrument (TROPOMI), launched in October 2017 on board the Sentinel-5 Precursor (S5P) satellite, monitors the composition of the Earth's atmosphere at an unprecedented horizontal resolution as fine as 3.5 × 5.5 km2. This paper assess the performances of the TROPOMI formaldehyde (HCHO) operational product compared to its predecessor, the OMI HCHO QA4ECV product, at different spatial and temporal scales. The parallel development of the two algorithms favored the consistency of the products, which facilitates the production of long-term combined time series. The main difference between the two satellite products is related to the use of different cloud algorithms, leading to a positive bias of OMI compared to TROPOMI of up to 30 % in Tropical regions. We show that after switching off the explicit correction for cloud effects, the two datasets come into an excellent agreement. For medium to large HCHO vertical columns (larger than 5 × 1015 molec.cm−2) the median bias between OMI and TROPOMI HCHO columns is not larger than 10 % (< 0.4 × 1015 molec.cm−2). For lower columns, OMI observations present a remaining positive bias of about 20 % (< 0.8 × 1015 molec.cm−2) compared to TROPOMI in mid-latitude regions. Here, we also use a global network of 18 MAX-DOAS instruments to validate both satellite sensors for a large range of HCHO columns. This work complements the study by Vigouroux et al. (2020) where a global FTIR network is used to validate the TROPOMI HCHO operational product. Consistent with the FTIR validation study, we find that for elevated HCHO columns, TROPOMI data are systematically low (−25 % for HCHO columns larger than 8 × 1015 molec.cm−2), while no significant bias is found for medium range column values. We further show that OMI and TROPOMI data present equivalent biases for large HCHO levels. However, TROPOMI significantly improves the precision of the HCHO observations at short temporal scales, and for low HCHO columns. We show that compared to OMI, the precision of the TROPOMI HCHO columns is improved by 25 % for individual pixels, and up to a factor 3 when considering daily averages in 20 km-radius circles. The validation precision obtained with daily TROPOMI observations is comparable to the one obtained with monthly OMI observations. To illustrate the improved performances of TROPOMI in capturing weak HCHO signals, we present clear detection of HCHO column enhancements related to shipping emissions in the Indian Ocean. This is achieved by averaging data over a much shorter period (3 months) than required with previous sensors, and opens new perspectives to study shipping emissions of VOCs and related atmospheric chemical interactions.

scholarly journals First estimates of global free-tropospheric NO<sub>2</sub> abundances derived using a cloud-slicing technique applied to satellite observations from the Aura Ozone Monitoring Instrument (OMI)

2014 ◽  
Vol 14 (19) ◽  
pp. 10565-10588 ◽  
Author(s):  
S. Choi ◽  
J. Joiner ◽  
Y. Choi ◽  
B. N. Duncan ◽  
A. Vasilkov ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Profile Analysis ◽  
Middle Latitude ◽  
Optical Absorption Spectroscopy ◽  
Ozone Monitoring Instrument ◽  
Vertical Column ◽  
Monitoring Instrument ◽  
Single Orbit ◽  
Tropospheric No2 ◽  
Ozone Monitoring

Abstract. We derive free-tropospheric NO2 volume mixing ratios (VMRs) by applying a cloud-slicing technique to data from the Ozone Monitoring Instrument (OMI) on the Aura satellite. In the cloud-slicing approach, the slope of the above-cloud NO2 column versus the cloud scene pressure is proportional to the NO2 VMR. In this work, we use a sample of nearby OMI pixel data from a single orbit for the linear fit. The OMI data include cloud scene pressures from the rotational-Raman algorithm and above-cloud NO2 vertical column density (VCD) (defined as the NO2 column from the cloud scene pressure to the top of the atmosphere) from a differential optical absorption spectroscopy (DOAS) algorithm. We compare OMI-derived NO2 VMRs with in situ aircraft profiles measured during the NASA Intercontinental Chemical Transport Experiment Phase B (INTEX-B) campaign in 2006. The agreement is generally within the estimated uncertainties when appropriate data screening is applied. We then derive a global seasonal climatology of free-tropospheric NO2 VMR in cloudy conditions. Enhanced NO2 in the free troposphere commonly appears near polluted urban locations where NO2 produced in the boundary layer may be transported vertically out of the boundary layer and then horizontally away from the source. Signatures of lightning NO2 are also shown throughout low and middle latitude regions in summer months. A profile analysis of our cloud-slicing data indicates signatures of lightning-generated NO2 in the upper troposphere. Comparison of the climatology with simulations from the global modeling initiative (GMI) for cloudy conditions (cloud optical depth > 10) shows similarities in the spatial patterns of continental pollution outflow. However, there are also some differences in the seasonal variation of free-tropospheric NO2 VMRs near highly populated regions and in areas affected by lightning-generated NOx.

scholarly journals Ozone profile retrievals from the Ozone Monitoring Instrument

2010 ◽  
Vol 10 (5) ◽  
pp. 2521-2537 ◽  
Author(s):  
X. Liu ◽  
P. K. Bhartia ◽  
K. Chance ◽  
R. J. D. Spurr ◽  
T. P. Kurosu
Keyword(s):  
Degrees Of Freedom ◽  
Optimal Estimation ◽  
Anthropogenic Pollution ◽  
Horizontal Resolution ◽  
Ozone Monitoring Instrument ◽  
Monitoring Instrument ◽  
Ozone Profile ◽  
Ozone Monitoring ◽  
The Tropics ◽  
Middle Stratosphere

Abstract. Ozone profiles from the surface to about 60 km are retrieved from Ozone Monitoring Instrument (OMI) ultraviolet radiances using the optimal estimation technique. OMI provides daily ozone profiles for the entire sunlit portion of the earth at a horizontal resolution of 13 km×48 km for the nadir position. The retrieved profiles have sufficient accuracy in the troposphere to see ozone perturbations caused by convection, biomass burning and anthropogenic pollution, and to track their spatiotemporal transport. However, to achieve such accuracy it has been necessary to calibrate OMI radiances carefully (using two days of Aura/Microwave Limb Sounder data taken in the tropics). The retrieved profiles contain ~6–7 degrees of freedom for signal, with 5–7 in the stratosphere and 0–1.5 in the troposphere. Vertical resolution varies from 7–11 km in the stratosphere to 10–14 km in the troposphere. Retrieval precisions range from 1% in the middle stratosphere to 10% in the lower stratosphere and troposphere. Solution errors (i.e., root sum square of precisions and smoothing errors) vary from 1–6% in the middle stratosphere to 6–35% in the troposphere, and are dominated by smoothing errors. Total, stratospheric, and tropospheric ozone columns can be retrieved with solution errors typically in the few Dobson unit range at solar zenith angles less than 80°.

scholarly journals S5P TROPOMI NO<sub>2</sub> slant column retrieval: method, stability, uncertainties and comparisons with OMI

2020 ◽  
Vol 13 (3) ◽  
pp. 1315-1335 ◽  
Author(s):  
Jos van Geffen ◽  
K. Folkert Boersma ◽  
Henk Eskes ◽  
Maarten Sneep ◽  
Mark ter Linden ◽  
...  
Keyword(s):  
Pacific Ocean ◽  
Superior Performance ◽  
Optical Absorption Spectroscopy ◽  
Statistical Uncertainty ◽  
Ozone Monitoring Instrument ◽  
Vertical Column ◽  
Retrieval Method ◽  
Monitoring Instrument ◽  
Offset Correction ◽  
The Stability

Abstract. The Tropospheric Monitoring Instrument (TROPOMI), aboard the Sentinel-5 Precursor (S5P) satellite, launched on 13 October 2017, provides measurements of atmospheric trace gases and of cloud and aerosol properties at an unprecedented spatial resolution of approximately 7×3.5 km2 (approx. 5.5×3.5 km2 as of 6 August 2019), achieving near-global coverage in 1 d. The retrieval of nitrogen dioxide (NO2) concentrations is a three-step procedure: slant column density (SCD) retrieval, separation of the SCD in its stratospheric and tropospheric components, and conversion of these into vertical column densities. This study focusses on the TROPOMI NO2 SCD retrieval: the retrieval method used, the stability of the SCDs and the SCD uncertainties, and a comparison with the Ozone Monitoring Instrument (OMI) NO2 SCDs. The statistical uncertainty, based on the spatial variability of the SCDs over a remote Pacific Ocean sector, is 8.63 µmol m−2 for all pixels (9.45 µmol m−2 for clear-sky pixels), which is very stable over time and some 30 % less than the long-term average over OMI–QA4ECV data (since the pixel size reduction TROPOMI uncertainties are ∼8 % larger). The SCD uncertainty reported by the differential optical absorption spectroscopy (DOAS) fit is about 10 % larger than the statistical uncertainty, while for OMI–QA4ECV the DOAS uncertainty is some 20 % larger than its statistical uncertainty. Comparison of the SCDs themselves over the Pacific Ocean, averaged over 1 month, shows that TROPOMI is about 5 % higher than OMI–QA4ECV, which seems to be due mainly to the use of the so-called intensity offset correction in OMI–QA4ECV but not in TROPOMI: turning that correction off means about 5 % higher SCDs. The row-to-row variation in the SCDs of TROPOMI, the “stripe amplitude”, is 2.15 µmol m−2, while for OMI–QA4ECV it is a factor of ∼2 (∼5) larger in 2005 (2018); still, a so-called stripe correction of this non-physical across-track variation is useful for TROPOMI data. In short, TROPOMI shows a superior performance compared with OMI–QA4ECV and operates as anticipated from instrument specifications. The TROPOMI data used in this study cover 30 April 2018 up to 31 January 2020.

scholarly journals Comparison and Validation of TROPOMI and OMI NO2 Observations over China

Atmosphere ◽  
2020 ◽  
Vol 11 (6) ◽  
pp. 636
Author(s):  
Chunjiao Wang ◽  
Ting Wang ◽  
Pucai Wang ◽  
Vadim Rakitin
Keyword(s):  
Spatial Resolution ◽  
Southern China ◽  
Correlation Coefficients ◽  
Absolute Difference ◽  
Optical Absorption Spectroscopy ◽  
Ozone Monitoring Instrument ◽  
Vertical Column ◽  
Seasonal Behavior ◽  
Monitoring Instrument ◽  
The Absolute

The new-generation sensor TROPOspheric Monitoring Instrument (TROPOMI) onboard the Sentinel 5 precursor (S5P) satellite is promising for monitoring air pollutants with greater spatial resolution, especially for China, which suffers from severe pollution. As tropospheric NO2 vertical column densities (VCDs) from TROPOMI have become available since February 2018, this study presents the comparisons of NO2 data measured by TROPOMI and its predecessor Ozone Monitoring Instrument (OMI) over China, together with validation against ground Multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements. At the nationwide scale, we used two different filters performed for the TROPOMI data (named TROPOMI50 and TROPOMI75), and the TROPOMI50 yielded larger values than TROPOMI75. The TROPOMI NO2 datasets from different filters show consistent spatial patterns with OMI, and the correlation coefficient values were both above 0.93. However, linear regression indicates that NO2 loadings in TROPOMI is about 2/3 to 4/5 of those in OMI, which is presumably due to a different cloud mask and uncertainties of air mass factors. The absolute difference is prominent over the high pollution areas such as Jing-Jin-Ji region and during winter and autumn, exceeding 0.6 × 1016 molecules cm−2 (molec cm−2). However, the NO2 concentrations retrieved from TROPOMI50 in the southern China may be somewhat higher than OMI. When it comes to the local-scale Jing-Jin-Ji hotspot, the analysis focuses on a comparison to TROPOMI75. TROPOMI manifests high quality and exhibits a significantly better performance of representing spatial variability. In contrast, OMI shows fewer effective pixels and does a poor job of capturing local details due to its row anomaly and low resolution. The absolute difference between two datasets shows the same seasonal behavior with NO2 variation, which is most striking in the winter (0.31 × 1016 molec cm−2) and is lowest in the summer (0.05 × 1016 molec cm−2). Furthermore, the ground MAX-DOAS instrument in Xianghe station, the representative site in Jing-Jin-Ji, is used to assess the skill of satellite retrievals. It turns out that both OMI and TROPOMI underestimate the observations, ranging from 30% to 50%, with OMI being less biased. In spite of the negative drift, the temporal structures of changes derived from OMI and TROPOMI closely match the ground-based records, since the correlation coefficients are above 0.8 and 0.95 for daily and monthly scales, respectively. Overall, TROPOMI NO2 retrievals are better suited for applications in China as well as the Jing-Jin-Ji hotspot due to its higher spatial resolution, although some improvements are also needed in the near future.

scholarly journals Ozone profile retrievals from the Ozone Monitoring Instrument

2009 ◽  
Vol 9 (5) ◽  
pp. 22693-22738 ◽  
Author(s):  
X. Liu ◽  
P. K. Bhartia ◽  
K. Chance ◽  
R. J. D. Spurr ◽  
T. P. Kurosu
Keyword(s):  
Optimal Estimation ◽  
Anthropogenic Pollution ◽  
Horizontal Resolution ◽  
Ozone Monitoring Instrument ◽  
Monitoring Instrument ◽  
The Earth ◽  
Ozone Profile ◽  
Ozone Monitoring ◽  
The Tropics ◽  
Middle Stratosphere

Abstract. Ozone profiles from the surface to about 60 km are retrieved from Ozone Monitoring Instrument (OMI) ultraviolet radiances using the optimal estimation technique. OMI provides daily ozone profiles for the entire sunlit portion of the earth at a horizontal resolution of 13 km×48 km for the nadir position. The retrieved profiles have sufficient accuracy in the troposphere to see ozone perturbations caused by convection, biomass burning and anthropogenic pollution, and to track their spatiotemporal transport. However, to achieve such accuracy it has been necessary to calibrate OMI radiances carefully (using two days of Aura/Microwave Limb Sounder data taken in the tropics). The retrieved profiles contain ~6–7° of freedom for signal, with 5–7 in the stratosphere and 0–1.5 in the troposphere. Vertical resolution varies from 7–11 km in the stratosphere to 10–14 km in the troposphere. Retrieval precisions range from 1% in the middle stratosphere to 10% in the lower stratosphere and troposphere. Solution errors (i.e., root sum square of precisions and smoothing errors) vary from 1–6% in the middle stratosphere to 6–35% in the troposphere, and are dominated by smoothing errors. Total, stratospheric, and tropospheric ozone columns can be retrieved with solution errors typically in the few Dobson unit range at solar zenith angles less than 80°.

scholarly journals Intercomparison of total column ozone data from the Pandora spectrophotometer with Dobson, Brewer, and OMI measurements over Seoul, Korea

2016 ◽  
Author(s):  
Jiyoung Kim ◽  
Jhoon Kim ◽  
Hi-Ku Cho ◽  
Jay Herman ◽  
Sang Seo Park ◽  
...  
Keyword(s):  
Optical Absorption Spectroscopy ◽  
Ozone Monitoring Instrument ◽  
Total Column Ozone ◽  
Monitoring Instrument ◽  
Ozone Monitoring ◽  
The Difference ◽  
Column Ozone ◽  
Observation Times ◽  
Total Column ◽  
Daily Total

Abstract. Daily total column ozone (TCO) measured using the Pandora spectrophotometer (#19) was intercompared with data from the Dobson (#124) and Brewer (#148) spectrophotometers, as well as from the Ozone Monitoring Instrument (OMI), over the 2-year period between March 2012 and March 2014 at Yonsei University, Seoul, Korea. The Pandora TCO measurements are closely correlated with those from the Dobson, Brewer, and OMI instruments with regression coefficients (slopes) of 0.95, 1.00, 0.98 (OMI-TOMS), and 0.97 (OMI-DOAS), respectively, and determination coefficients (R2) of 0.95, 0.97, 0.96 (OMI-TOMS), and 0.95 (OMI-DOAS), respectively. In particular, they show a close agreement with the Brewer TCO measurements, with slope and R2 values of 1.00 and 0.97, respectively. The difference between the Pandora and Dobson data can be explained by smaller amount of Dobson data available to calculate the daily averages, observation times, solar zenith angles, SO2 effect, temperature, and humidity between the two datasets. The difference in the results obtained from the Pandora instrument and Ozone Monitoring Instrument-Differential Optical Absorption Spectroscopy (OMI-DOAS algorithm) can be explained by the dependence on seasonal variations of about ± 2 % and solar zenith angle leading to overestimation by 5 % of OMI-DOAS measurements. For the Dobson measurements in particular, the difference caused by the inconsistency in observation times when compared with the Pandora measurements was up to 12.5 % on 22 June 2013 because of diurnal variations in the TCO values. However, despite these various differences and discrepancies, the daily TCO values measured by the four instruments during the 2-year study period are accurate and closely correlated.

scholarly journals Seasonal variation of tropospheric bromine monoxide over the Rann of Kutch salt marsh seen from space

2016 ◽  
Vol 16 (20) ◽  
pp. 13015-13034 ◽  
Author(s):  
Christoph Hörmann ◽  
Holger Sihler ◽  
Steffen Beirle ◽  
Marloes Penning de Vries ◽  
Ulrich Platt ◽  
...  
Keyword(s):  
Salt Marsh ◽  
Monsoon Season ◽  
Point Sources ◽  
Optical Absorption Spectroscopy ◽  
Polar Regions ◽  
Ambient Conditions ◽  
Ozone Monitoring Instrument ◽  
Vertical Column ◽  
Monitoring Instrument ◽  
Ozone Monitoring

Abstract. The Rann of Kutch (India and Pakistan) is one of the largest salt deserts in the world. Being a so-called "seasonal salt marsh", it is regularly flooded during the Indian summer monsoon. We present 10 years of bromine monoxide (BrO) satellite observations by the Ozone Monitoring Instrument (OMI) over the Great and Little Rann of Kutch. OMI spectra were analysed using Differential Optical Absorption Spectroscopy (DOAS) and revealed recurring high BrO vertical column densities (VCDs) of up to 1.4  ×  1014 molec cm−2 during April/May, but no significantly enhanced column densities during the monsoon season (June–September). In the following winter months, the BrO VCDs are again slightly enhanced while the salty surface dries up. We investigate a possible correlation of enhanced reactive bromine concentrations with different meteorological parameters and find a strong relationship between incident UV radiation and the total BrO abundance. In contrast, the second Global Ozone Monitoring Instrument (GOME-2) shows about 4 times lower BrO VCDs over the Rann of Kutch than found by OMI and no clear seasonal cycle is observed. One reason for this finding might be the earlier local overpass time of GOME-2 compared to OMI (around 09:30 vs. 13:30 LT), as the ambient conditions significantly differ for both satellite instruments at the time of the measurements. Further possible reasons are discussed and mainly attributed to instrumental issues. OMI additionally confirms the presence of enhanced BrO concentrations over the Dead Sea valley (Israel/Jordan), as suggested by former ground-based observations. The measurements indicate that the Rann of Kutch salt marsh is probably one of the strongest natural point sources of reactive bromine compounds outside the polar regions and is therefore supposed to have a significant impact on local and regional ozone chemistry.

scholarly journals Global free tropospheric NO<sub>2</sub> abundances derived using a cloud slicing technique applied to satellite observations from the Aura Ozone Monitoring Instrument (OMI)

2014 ◽  
Vol 14 (2) ◽  
pp. 1559-1615 ◽  
Author(s):  
S. Choi ◽  
J. Joiner ◽  
Y. Choi ◽  
B. N. Duncan ◽  
E. Bucsela
Keyword(s):  
Boundary Layer ◽  
Profile Analysis ◽  
Middle Latitude ◽  
Optical Absorption Spectroscopy ◽  
Ozone Monitoring Instrument ◽  
Vertical Column ◽  
Monitoring Instrument ◽  
Single Orbit ◽  
Tropospheric No2 ◽  
Ozone Monitoring

Abstract. We derive free-tropospheric NO2 volume mixing ratios (VMRs) and stratospheric column amounts of NO2 by applying a cloud slicing technique to data from the Ozone Monitoring Instrument (OMI) on the Aura satellite. In the cloud-slicing approach, the slope of the above-cloud NO2 column vs. the cloud scene pressure is proportional to the NO2 VMR. In this work, we use a sample of nearby OMI pixel data from a single orbit for the linear fit. The OMI data include cloud scene pressures from the rotational-Raman algorithm and above-cloud NO2 vertical column density (VCD) (defined as the NO2 column from the cloud scene pressure to the top-of-the-atmosphere) from a differential optical absorption spectroscopy (DOAS) algorithm. Estimates of stratospheric column NO2 are obtained by extrapolating the linear fits to the tropopause. We compare OMI-derived NO2 VMRs with in situ aircraft profiles measured during the NASA Intercontinental Chemical Transport Experiment Phase B (INTEX-B) campaign in 2006. The agreement is generally within the estimated uncertainties when appropriate data screening is applied. We then derive a global seasonal climatology of free-tropospheric NO2 VMR in cloudy conditions. Enhanced NO2 in the free troposphere commonly appears near polluted urban locations where NO2 produced in the boundary layer may be transported vertically out of the boundary layer and then horizontally away from the source. Signatures of lightning NO2 are also shown throughout low and middle latitude regions in summer months. A profile analysis of our cloud slicing data indicates signatures of uplifted and transported anthropogenic NO2 in the middle troposphere as well as lightning-generated NO2 in the upper troposphere. Comparison of the climatology with simulations from the Global Modeling Initiative (GMI) for cloudy conditions (cloud optical thicknesses > 10) shows similarities in the spatial patterns of continental pollution outflow. However, there are also some differences in the seasonal variation of free-tropospheric NO2 VMRs near highly populated regions and in areas affected by lightning-generated NOx. Stratospheric column NO2 obtained from cloud slicing agrees well with other independently-generated estimates, providing further confidence in the free-tropospheric results.

scholarly journals Seasonal variation of tropospheric bromine monoxide over the Rann of Kutch salt marsh seen from space

2016 ◽  
Author(s):  
C. Hörmann ◽  
H. Sihler ◽  
S. Beirle ◽  
M. J. M. Penning de Vries ◽  
U. Platt ◽  
...  
Keyword(s):  
Salt Marsh ◽  
Monsoon Season ◽  
Strong Relationship ◽  
Point Sources ◽  
Optical Absorption Spectroscopy ◽  
Polar Regions ◽  
Ambient Conditions ◽  
Ozone Monitoring Instrument ◽  
Monitoring Instrument ◽  
Ozone Monitoring

Abstract. The Rann of Kutch (India/Pakistan) is one of the largest salt deserts in the world. Being a so-called 'seasonal salt marsh', it is regularly flooded during the Indian Summer Monsoon. We present 10 years of bromine monoxide (BrO) satellite observations by the Ozone Monitoring Instrument (OMI) over the Great and Little Rann of Kutch. OMI spectra were analysed using Differential Optical Absorption Spectroscopy (DOAS) and revealed recurring high BrO VCDs up to 1.4 × 1014 molec/cm2 during April/May, but no significantly enhanced column densities during the monsoon season (June–September). In the following winter months, the BrO VCDs are again slightly enhanced while the salty surface dries up. We investigate a possible correlation of enhanced reactive bromine concentrations with different meteorological parameters and find a strong relationship between incident UV radiation and the total BrO abundance. In contrast, the second Global Ozone Monitoring Instrument (GOME-2) shows about four times lower BrO VCDs over the Rann of Kutch than found by OMI and no clear seasonal cycle is observed. One reason for this finding might be the earlier local overpass time of GOME-2 compared to OMI (around 9:30 vs. 13:30 LT), as the ambient conditions significantly differ for both satellite instruments at the time of the measurements. Further possible reasons are discussed and mainly attributed to instrumental issues. OMI additionally confirms the presence of enhanced BrO concentrations over the Dead Sea valley (Israel/Jordan), as suggested by former ground-based observations. The measurements indicate that the Rann of Kutch salt marsh is probably one of the strongest natural point sources of reactive bromine compounds outside the polar regions and is therefore supposed to have an significant impact on local and regional ozone chemistry.

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