NO2 Pollution Hotspots: European Union, Change vs Year Earlier (%)

## What this measures

The percent change in nitrogen dioxide (NO2) over European Union's most polluted areas (its cities, industry and power plants) from the same month a year earlier, measured from space by the Copernicus Sentinel-5P satellite.

## Why it matters

NO2 comes mostly from burning fuel and lasts only hours, so a fall from a year earlier means less burning in factories, power plants and traffic, and a rise means more. The satellite sees every country the same way and the month is in within days, so it is an early, independent check on industrial activity. From 2021 to 2026 the three-month average of this change moved with euro-area industrial production's 12-month change (macro.eurostat.ea_industrial_production_yoy): a correlation of about 0.5 in the same month.

## How to read it

Above zero means more NO2 than a year earlier. Comparing with the same month removes the strong seasonal cycle, but not the weather: the change often moves 10 points from one month to the next, and sometimes 20 or more, so read the average of several months. A long downward drift comes from cleaner engines and plants, not only from lower output.

## What it does not say

It is not a measure of output: emission controls, fuel switching (coal to gas, cars to electric) and weather all move it. It cannot separate industry from traffic or power. The satellite record is one instrument, but its processing changed over time (processor versions 2.4 to 2.9). KNMI advises using data from version 2.6 (November 2023 to September 2024) with care, because of a cloud-algorithm issue later rolled back, and notes that version 2.9.1 (from 22 November 2025) may show a small step in the record. A change that crosses one of those dates can carry part of the step.

## How it's built

The month's value of no2.trop_column_hotspots.eu (see its methodology for the hotspot cells and how cloud gaps are handled) divided by the same month a year earlier, minus one, in percent. From May 2019.

## Source

Contains modified Copernicus Sentinel data (2018–2026), processed by KNMI: monthly mean tropospheric NO2 from TROPOMI on Sentinel-5P, TEMIS service (temis.nl). Boundaries: Natural Earth. Palanor calculation. Refreshed by /api/cron/no2-sync.