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Winter is coming – with polluted air

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Colder weather, traffic and heating mean poorer air

Poor air quality remains one of the major risk factors for early death worldwide, a fact maybe not at the forefront of our minds in the midst of the Covid-19 pandemic. Winter normally brings poorer air, and 2020 is unfortunately no exception.

Europe – local traffic and winds from south east

Particle levels have risen sharply over western parts of Europe the last days. The particle levels in English cities have been remarkably high, but central Europe and even parts of Scandinavia get their share of particle pollution.

Winds from south east in combination with local pollution are very likely the reasons behind the poor air. The wind transports particles from the southeastern part of Europe towards the northwestern part of the continent, similar to what happened in early October. The particles could stem from industrial plants or agricultural areas.

Simulation of PM2.5 concentration over Europe, 9-12 November 2020. Video from Windy.com.

From London to Warsaw

As we can see from the illustrations below, London experienced a severe episode of air pollution at the start of the weekend. The air quality was poor over large parts of England, possibly linked to cold air and weak winds trapping the pollution.

Warsaw follows its annual pattern with more air pollution during the winter months, as coal-fired power is the major power source for heating.

The Oslo area in Norway sees a similar pattern, albeit with much lower pollution levels. However, the hourly breakdown reveals a clear pattern, with traffic (and possibly wood burning in homes) driving air pollution in afternoons. We see less effect of the south eastern winds for this region.

Dashed line shows WHO guideline for annual mean. Values in μg/m3. Data sourced from OpenAQ.org.
Warszawa - monthly pm2.5 2020
Dashed line shows WHO guideline for annual mean. Data sourced from OpenAQ.org. Values in μg/m3.
Bærum pm25 monthly 2020
Dashed line shows WHO guideline for annual mean. Data sourced from OpenAQ.org. Values in μg/m3.
London pm2.5 01-08 Nov
Dashed line shows WHO guideline for 24hrs mean. Data sourced from OpenAQ.org. Values in μg/m3.
Warszawa hourly pm25 1-8 nov 20
Dashed line shows WHO guideline for 24hrs mean. Data sourced from OpenAQ.org. Values in μg/m3.
Bærum hourly pm25 1-8 nov 20
Dashed line shows WHO guideline for 24hrs mean. Data sourced from OpenAQ.org. Values in μg/m3.

Delhi chokes on poor air

If we move across to the Indian subcontinent, we see the same yearly pattern with higher air pollution levels in winter. Northern India and the country’s capital is currently draped in really, really bad air. Levels tend to be hazardous or very unhealthy during the colder winter months, and 2020 is no exception.

Local pollution, such as traffic, and crop burning in neighbouring states are the major contributors to the particle pollution. In combination with dry weather and weak winds, this makes a deadly combination. Delhi is not helped by its geography either, with the Himalayas trapping air on the Indo-Gangetic plain.

Delhi pm25 monthly 2020
hed line shows WHO guideline for annual mean. Data sourced from OpenAQ.org. Values in μg/m3.
Delhi hourly pm25 01-08 Nov 20
Data sourced from OpenAQ.org. Values in μg/m3.

Stubble burning aggravates the situation

As shown below, the modelled pm2.5 levels over Northern India correspond well with fire intensity. The fires are most likely from crop stubble burning, as farmers burn their stubble to prepare for the next growing season.

Simulation of PM2.5 concentration over Northern India, 9-12 November 2020. Video from Windy.com.
Fire intensity around Delhi 09 Nov 20. Image from Windy.com.

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