Retrieval of total column and surface NO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; from Pandora zenith-sky measurements

Zhao, Xiaoyi; Griffin, Debora; Fioletov, Vitali; McLinden, Chris A.; Davies, J.; Ogyu, Akira; Lee, Sum Chi; Lupu, A.; Moran, Michael D.; Cede, Alexander; Tiefengraber, Martin; Müller, Moritz

doi:10.5194/acp-19-10619-2019

Cited by 17 publications

(22 citation statements)

References 92 publications

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“…As compared to previous satellite-based instruments such as OMI, the mean bias against ground-based observations in Helsinki is of the same order of magnitude while the correlation coefficient is generally higher (r = 0.68 for TROPOMI and r = 0.5 for OMI, see Ialongo et al, 2016). The correlation between Pandora and TROPOMI NO 2 retrievals is also in line with the results obtained by Griffin et al (2019) over the Canadian oil sands.…”

Section: Discussionsupporting

confidence: 83%

“…Pandora measures direct sunlight in the UV-VIS (ultraviolet-visible) spectral range (280-525 nm) and provides NO 2 total columns using the direct-sun DOAS (Differential Optical Absorption Spectroscopy) technique (Herman et al, 2009). Recently, Zhao et al (2019) presented a method to derive NO 2 total columns from Pandora zenith-sky measurements as well.…”

mentioning

confidence: 99%

“…Very recently, Griffin et al (2019) presented first results of the validation of TROPOMI NO 2 retrievals over the Canadian oil sands using air-mass factors calculated with the high-resolution GEM-MACH model. They show how the TROPOMI NO 2 vertical column densities are highly correlated with ground-based observations and agree within 15-30 %.…”

mentioning

confidence: 99%

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Comparison of TROPOMI/Sentinel 5 Precursor NO2 observations with ground-based measurements in Helsinki

Ialongo¹,

Virta²,

Eskes³

et al. 2019

Preprint

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Abstract. We present a comparison between satellite-based TROPOMI (TROPOspheric Monitoring Instrument) NO2 products and ground-based observations in Helsinki (Finland). TROPOMI NO2 total (summed) columns are compared with the measurements performed by the Pandora spectrometer during April–September 2018. We find a high correlation (r = 0.68) between satellite- and ground-based data, but also that TROPOMI total columns underestimate ground-based observations for relatively large Pandora NO2 total columns, corresponding to episodes of relatively elevated pollution. This is expected because of the relatively large size of the TROPOMI ground pixel (3.5 km x 7 km) and the a-priori used in the retrieval compared to the relatively small field-of-view of the Pandora instrument. Replacing the coarse a-priori NO2 profiles with high-resolution profiles from the CAMS chemical transport model improves the agreement between TROPOMI and Pandora total columns for episodes of NO2 enhancement. We also analyse the consistency between satellite-based data and in situ NO2 surface concentrations measured at the Helsinki-Kumpula air quality station (located a few metres from the Pandora spectrometer). We find similar day-to-day variability between TROPOMI, Pandora and in situ measurements, with NO2 enhancements observed during the same days. Both satellite- and ground-based data show a similar weekly cycle, with lower NO2 levels during the weekend compared to the weekdays as a result of reduced emissions from traffic and industrial activities (as expected in urban sites). The TROPOMI NO2 maps reveal also spatial features, such as the main traffic ways and the airport area, as well as the effect of the prevailing south-west wind patterns. This is one of the first works in which TROPOMI NO2 retrievals are validated against ground-based observations and the results provide an early evaluation of their applicability for monitoring pollution levels in urban sites. Overall, TROPOMI retrievals are valuable to complement the ground-based air quality data (available with high temporal resolution) for describing the spatio-temporal variability of NO2, even in a relatively small city like Helsinki.

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Section: Discussionsupporting

confidence: 83%

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confidence: 99%

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Comparison of TROPOMI/Sentinel 5 Precursor NO2 observations with ground-based measurements in Helsinki

Ialongo¹,

Virta²,

Eskes³

et al. 2019

Preprint

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“…12a shows the Pandora NO2 measured at Downsview has 0.03 DU random uncertainty (red cross sign 15 with error bar), which is better than the Pandora total column NO2 nominal accuracy (0.05 DU at 1-sigma level, e.g. (Zhao et al, 2019b)). At Downsview, the TROPOMI KNMI and TROPOMI ECCC total column data products have random uncertainties of 0.05 DU (red square with error bar, Fig.…”

Section: Precision and Accuracymentioning

confidence: 93%

Assessment of the quality of TROPOMI high-spatial-resolution NO2 data products

Zhao

Griffin

Fioletov

et al. 2019

Preprint

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Abstract. The TROPOspheric Monitoring Instrument (TROPOMI) on-board 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 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 (used 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. 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 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 five. Using 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, demonstrating benefits from the high-resolution regional air quality forecast model.

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“…Note, though, that operator splitting is employed to integrate the GEM-MACH chemistry module and some processes such as gas-phase chemistry may be solved using much smaller time steps. GEM-MACH performance has been evaluated in a number of ways against surface AQ measurements (Chen et al 2019; Moran et al 2018aMoran et al , 2019aPavlovic et al 2016;Robichaud et al 2016;Stroud et al 2020;Zhao et al 2019) and against peer models (Im et al 2015b;Im et al 2015a;Wang et al 2015) for different model versions and time periods. To best align with the present study, Table S2 summarizes objective scores for NO 2 , O 3 , and PM 2.5 for recent periods in the summer of 2019 and winter of 2020 for the same model version (v3.0) and same Canadian projected 2020 emissions inventory as used in the present study.…”

Section: Model and Simulation Descriptionmentioning

confidence: 99%

Isolating the impact of COVID-19 lockdown measures on urban air quality in Canada

Mashayekhi

Pavlovic

Racine

et al. 2021

Air Qual Atmos Health

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We have investigated the impact of reduced emissions due to COVID-19 lockdown measures in spring 2020 on air quality in Canada’s four largest cities: Toronto, Montreal, Vancouver, and Calgary. Observed daily concentrations of NO2, PM2.5, and O3 during a “pre-lockdown” period (15 February–14 March 2020) and a “lockdown” period (22 March–2 May 2020), when lockdown measures were in full force everywhere in Canada, were compared to the same periods in the previous decade (2010–2019). Higher-than-usual seasonal declines in mean daily NO2 were observed for the pre-lockdown to lockdown periods in 2020. For PM2.5, Montreal was the only city with a higher-than-usual seasonal decline, whereas for O3 all four cities remained within the previous decadal range. In order to isolate the impact of lockdown-related emission changes from other factors such as seasonal changes in meteorology and emissions and meteorological variability, two emission scenarios were performed with the GEM-MACH air quality model. The first was a Business-As-Usual (BAU) scenario with baseline emissions and the second was a more realistic simulation with estimated COVID-19 lockdown emissions. NO2 surface concentrations for the COVID-19 emission scenario decreased by 31 to 34% on average relative to the BAU scenario in the four metropolitan areas. Lower decreases ranging from 6 to 17% were predicted for PM2.5. O3 surface concentrations, on the other hand, showed increases up to a maximum of 21% close to city centers versus slight decreases over the suburbs, but Ox (odd oxygen), like NO2 and PM2.5, decreased as expected over these cities.

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Retrieval of total column and surface NO<sub>2</sub> from Pandora zenith-sky measurements

Cited by 17 publications

References 92 publications

Comparison of TROPOMI/Sentinel 5 Precursor NO<sub>2</sub> observations with ground-based measurements in Helsinki

Comparison of TROPOMI/Sentinel 5 Precursor NO<sub>2</sub> observations with ground-based measurements in Helsinki

Assessment of the quality of TROPOMI high-spatial-resolution NO<sub>2</sub> data products

Isolating the impact of COVID-19 lockdown measures on urban air quality in Canada

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Retrieval of total column and surface NO&lt;sub&gt;2&lt;/sub&gt; from Pandora zenith-sky measurements

Cited by 17 publications

References 92 publications

Comparison of TROPOMI/Sentinel 5 Precursor NO&lt;sub&gt;2&lt;/sub&gt; observations with ground-based measurements in Helsinki

Comparison of TROPOMI/Sentinel 5 Precursor NO&lt;sub&gt;2&lt;/sub&gt; observations with ground-based measurements in Helsinki

Assessment of the quality of TROPOMI high-spatial-resolution NO&lt;sub&gt;2&lt;/sub&gt; data products

Isolating the impact of COVID-19 lockdown measures on urban air quality in Canada

Contact Info

Product

Resources

About

Retrieval of total column and surface NO<sub>2</sub> from Pandora zenith-sky measurements

Comparison of TROPOMI/Sentinel 5 Precursor NO<sub>2</sub> observations with ground-based measurements in Helsinki

Comparison of TROPOMI/Sentinel 5 Precursor NO<sub>2</sub> observations with ground-based measurements in Helsinki

Assessment of the quality of TROPOMI high-spatial-resolution NO<sub>2</sub> data products