The air quality in Flanders is getting worse … while getting better

The VRT news item from last post not only listed how we already feel the effects of “global warming” in Flanders, but also four ways in which “climate change” will affect Flanders in the future. One of those is:

  • The air quality is getting worse. Higher temperatures lead to more ozone in the air, and also particulate matter will peak.

That statement really surprised me. When I compare to when I was a kid, air quality has improved, nay, vastly improved. Back then, there were no filters in car exhausts, factories spewed their exhaust gases directly in the air, there still was heavy industry back then, houses were heated by coal or oil,… I don’t know the age of the one who wrote this, but from my personal experience I am not really agreeing.

The two components that apparently made the difference are ozone and particulate matter. Ozone was quite a lot in the media a decade ago when we heard a lot about ozone pollution. Ozone increases under certain circumstances like heatwaves, low wind speed and wind from East, South or South-East direction, absence of precipitation or substances that break it down,,… But during the last years I didn’t hear much about it anymore. Particulate matter is different in that regard. The last years it is often in the media and described as a problem. However, in the MIRA report I couldn’t find a trend or a graph from ozone or particulate matter. So I became rather curious about how big that increase actually is, given that global warming is already here, ya know.

To my surprise, the ozone level trend isn’t even rising (the levels of Flanders in orange):

After an increase in the 1990s, it seems more like a nice flat line to me in the last 15 years. Strangely if we get to hear that on average we get one heatwave every year, compared to one in every three years in the 1970s. By the way, as said in previous post, that statement is actually true (but only if one ignores the data before the 1970s in which we got 1.5 heatwaves on average per year in the 1940s, compared to the average of that 1 every year in the last decade 🙂 ).

The annual Ozone concentration trend is only part of the story. It doesn’t take into account the burden on the public. There is an indicator that takes this into account: AOT60. It stands for Accumulated Ozone Exposure above a Threshold of 60 ppb or 120 µg/m3. It is the cumulative excess above the threshold value of 120 µg/m3 per day multiplied by the duration (in hours). It considers the size and duration of the exceedance and is considered an indicator to quantify the excess burden on public health. This is its trend (for Belgium, didn’t find one for Flanders):

If there is any trend, it seems to be going down. So despite all these heatwaves that are battering our little country, the negative effect somehow seems to be diminishing.

I was very interested in the trend of particulate matter as the media describe it as a serious problem. To my surprise this is the trend of PM10 fraction (particulate matter with an aerodynamic diameter less than 10 micrometer):

The number of days with daily mean PM10 > 50 µg/m3:

The annual mean for the PM2.5 fraction:

This is not what we hear from the media! This is also not what the press release is trying to tell us.

I am a bit at a loss why they think that the air quality (ozone and particulate matter) is getting WORSE and how particulate matter will PEAK in the future, considering that the trend is actually going down for at least the last decade and a half, even while already experiencing those horrible effects of global warming right now…


2 thoughts on “The air quality in Flanders is getting worse … while getting better

  1. manicbeancounter

    You have researched this well. There is a curiosity that you might be able to resolve. If ozone is a pollutant is like particulates I would expect it to rise with population density in a single country. But ozone levels are higher in Wallonia than Flanders with less than half the population density. In turn Flanders has higher ozone levels than Brussels with less than a tenth of the population density.
    PM2.5 concentrations are more what I would expect.


    1. trustyetverify Post author

      Indeed, ozone levels in Wallonia are higher than Flanders or Brussels which are more densely populated. In general, there is also more ozone in rural areas than in cities and more in the weekend than during weekdays. This seems counterintuitive, but there is a logical explanation for it. Ozone is not a “primary pollutant” (one that is emitted) like particulate matter, but it is a “secondary pollutant” (one that is formed when primary pollutants react in the atmosphere).

      In its most simple form it goes like this: nitrogen dioxide (NO2) react with oxygen (O2) to form nitrogen monoxide (NO) and ozone (O3):

      NO2 + O2 ⇌ NO + O3

      This reaction goes both ways, so ozone can break down again in the presence of nitrogen monoxide.

      There is more nitrogen monoxide in cities (via reaction with volatile organic compounds from traffic) than in rural areas, therefor ozone will break down more in cities and as a consequence the ozone level goes down (and nitrogen dioxide level goes up).

      In rural areas there is less traffic, therefor less nitrogen monoxide, therefor less break down of ozone.

      The same explanation for the higher ozone levels in Wallonia and during the weekend.



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