nitrogen_dioxide

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Responsible:Niccolò Calandri

Nitrogen Dioxide — Sentinel-5P TROPOMI NO2

Overview

The Nitrogen Dioxide (NO₂) layer measures the tropospheric column density of NO₂ using the TROPOMI instrument aboard Sentinel-5P. NO₂ is one of the most important indicators of air quality and a key precursor to:

Tropospheric ozone (O₃) formation
Fine particulate matter (PM2.5) via secondary aerosol formation
Acid deposition (contributing to acid rain)

Sources of NO₂:

Anthropogenic (~70 %): road traffic, power plants, industrial combustion, shipping
Natural (~30 %): lightning-produced NOₓ, soil microbial processes

NO₂ has a short atmospheric lifetime of approximately 1 day, making it an excellent tracer of local emission sources. High concentrations are typically observed over cities, highways, power plants, and industrial zones. Native resolution: ~1113 m, output: 100 m.

Calculation Methodology

Retrieval algorithm:

The tropospheric NO₂ column is retrieved using DOAS (Differential Optical Absorption Spectroscopy) in the visible range (405–465 nm):

Total slant column fitting in the 405–465 nm window
Stratospheric separation using data assimilation (TM5-MP chemistry transport model)
Tropospheric column = Total column − Stratospheric column
Air mass factor conversion accounting for surface albedo, aerosols, and terrain height
Quality filtering based on cloud radiance fraction (< 0.5) and QA flags

Typical concentrations:

Environment	NO₂ Column (µmol/m²)
Remote/ocean	< 2
Rural	2–5
Suburban	5–15
Urban	15–50
Industrial hotspots	> 50

Data Sources

Code	Name	Provider	Type	Coverage	Resolution	Availability
`COPERNICUS/S5P/OFFL/L3_NO2`	Sentinel-5P TROPOMI NO2 L3	ESA/Copernicus	Atmospheric column	Global	~1113 m	2018-06 — present

Documentation: GEE S5P NO2

Technical Notes

The short lifetime of NO₂ (~1 day) means satellite observations closely reflect local emission patterns
Weekend/weekday differences are clearly visible in NO₂ data over urban areas
COVID-19 lockdowns (2020) produced historically unprecedented NO₂ reductions over major cities
Cloud contamination reduces data availability, especially in winter months at high latitudes
The 13:30 local overpass time captures afternoon conditions; morning rush-hour peaks may be underrepresented

References

Veefkind, J.P. et al. (2012). "TROPOMI on the ESA Sentinel-5 Precursor: A GMES mission for global observations of the atmospheric composition". Remote Sensing of Environment, 120, pp. 70–83.
van Geffen, J., Eskes, H., Boersma, K.F. et al. (2020). "S5P TROPOMI NO2 slant column retrieval: method, stability, uncertainties and comparisons". Atmos. Meas. Tech., 13, pp. 1315–1335.
Goldberg, D.L. et al. (2021). "Disentangling the impact of the COVID-19 lockdowns on urban NO₂ from natural variability". Geophysical Research Letters, 48, e2020GL089269.

Data Sources & References

Sources

WRD_S5NO2_99

Methodology

Il biossido di azoto (NO2) viene mappato utilizzando i dati Sentinel-5P TROPOMI (TROPOspheric Monitoring Instrument), prodotto OFFL L3_NO2 disponibile su Google Earth Engine. Il NO2 è un gas traccia importante nell'atmosfera, prodotto principalmente da combustione di combustibili fossili (traffico, centrali elettriche, industrie - circa 70%) e da fonti naturali (fulmini, processi microbiologici - circa 30%). Con un tempo di vita in atmosfera di circa 1 giorno, è un ottimo tracciante di emissioni locali e indicatore chiave della qualità dell'aria e dell'inquinamento urbano/industriale. La risoluzione nativa è di circa 1113 metri (0.01° a nadir, ~5.5 km x 3.5 km al suolo). La banda utilizzata è 'tropospheric_NO2_column_number_density', che misura la densità colonnare troposferica di NO2 in mol/m². Le acquisizioni vengono filtrate per qualità (qa_value > 0.5) per escludere pixel con alta incertezza. Viene applicato un ricampionamento bilineare per migliorare la risoluzione apparente da ~1km a 100m, quindi calcolata la media pixel-wise sul periodo selezionato. Per aree estese, il download avviene in quadranti paralleli con successivo merge.