NO2 Pollution: Inner Mongolia, China (Sentinel-5P, monthly)

## What this measures

The average amount of nitrogen dioxide (NO2) in the lower atmosphere over Inner Mongolia province, China each month, measured from space by the TROPOMI instrument on the European Copernicus Sentinel-5P satellite. The unit is the tropospheric column: the NO2 between the ground and roughly 10 km up, in 10^15 molecules per square centimetre of ground.

## Why it matters

NO2 comes mostly from burning fuel: power plants, factories, heavy trucks, ships and cars. It lasts only hours, so it stays near where it was emitted and changes as soon as activity changes. That makes it one of the few measures of economic activity that can be seen from space, the same way in every country, and within days of the month's end, well before official industrial statistics.

## How to read it

Higher means more NO2 over the area. NO2 has a strong seasonal cycle. In winter the sun is weaker, so NO2 breaks down more slowly, and heating adds emissions: over cities and industry, winter months often read two to three times as high as summer ones. Compare a month with the same month in earlier years, never with the month before. Wind, rain and cloud move single months a lot, so read several months together.

## What it does not say

It is a column of gas, not a count of emissions: weather and chemistry change it as well as fuel burning, and it does not say which source the NO2 came from. Lightning, soils and fires add NO2 too, mainly in summer. 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.

## How it's built

Each month KNMI averages the TROPOMI observations that pass its quality screening on a grid of 0.125° cells (about 14 km). Where no observation passes in a month, usually because of persistent cloud or snow and ice cover, the cell has no value. Palanor leaves those cells out and publishes a month only when cells with a value cover at least half of the area; in China's far north-east some winter months are missing for this reason. Palanor takes the area-weighted mean of the cells whose centre lies inside Inner Mongolia (boundaries from Natural Earth). History from May 2018, the start of the reprocessed record.

## 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.