Healthy air is a top concern for most Flemish citizens. And rightly so. Yet, current media interest often does injustice to the great complexity inherent in this problem. So for a clear perspective, we highlight five elements that are not sufficiently present in the debate.

Don’t alarm. Inform!

The quality of the air in which we live and which we continuously breathe is constantly evolving. Yet the issue of air quality almost only seems to ever make the news when something happens, i.e. when maximum limits or warning thresholds are exceeded. This – quite simply – is how the news cycle works.

However, the average annual concentrations of various pollutants (ozone is a special case) have fallen considerably over the past decades. Thus broadly speaking, air quality has improved in the Flemish Region. Yet this rarely shows up in the news. Remarkable finding: the number of healthy years of life lost through exposure to particulate matter (expressed per population) fell by a factor of one and a half in the period 2005-2016. This too we hardly hear, see or read about.

Could it be that a more nuanced interpretation of the full impact of the interaction of particulate matter, soot, ozone, sulphur and nitrogen dioxide on human health is too complex, and therefore not flashy enough?

Why is it that attention to air quality has increased so much in recent years? There are several explanations for this. Since the beginning of the nineties, for example, diverse standards and targets have been  developed (for Flanders, for Europe …), and these standards naturally generate attention when they are exceeded. In addition, scientists have gained many new insights, for example into the impact of different pollutants on human health. In Flanders a link was recently established between exposure to particulate matter and numerous medical (risk) factors such as increased (repairable) DNA damage, inflammation of the airways, allergic reactions such as asthma and rhinitis, and stress for pregnant women.

Due to technological progress and the pressure of public opinion, today measurements are made much more thoroughly, accurately and – especially – more detailed. This results in maps and models with a higher information density that reveal local differences. VITO for example recently launched the new ATMO Street Model that shows air pollution down to the level of individual streets. This more accurate knowledge of local concentrations and exposure allows the impact on health to be better mapped. However, finding the direct health effects of each individual pollutant remains a major challenge.

Citizen science par excellence

Science and technology are often a remote concern. This, however, is not the case with respect to research into air quality and the corresponding corrective measures. Since this concerns one’s own living environment, citizens are prepared to gather information themselves. This is citizen science par excellence. The fact that the issue of air quality could become a dream test case for citizen science is the result of various developments.

One of these developments is the high information density of the pollution modelling maps containing measurement data. Because the model maps are more detailed, and therefore more local, individuals obtain a reliable picture of the air quality in their immediate surroundings, near their children’s school, or along their daily commute.

Plus, cheaper and more convenient measuring devices and apps have been introduced in recent years that allow individuals to do the work themselves. At VITO, for example, the airQmap platform was developed that allows volunteers to contribute to air quality measurement at street level themselves. However, caution is required here: not all devices available on the market provide equally high-quality data.

Reliable equipment and information are a powerful lever for motivating individuals: to participate in largescale projects or to demand from government an effective policy to improve air quality. The citizen science project Curieuzeneuzen [“curious noses”] – supported by governments, private partners and the academic world – is a first if only due to its scope. Because of its high ambition, Curieuzeneuzen makes it clear that citizen science entails both a great opportunity and a challenge. Thanks to the free deployment of twenty thousand volunteers, an enormous amount of fine-grained data can be generated: something that scientists in other research projects normally can only dream of. On the other hand, this pile of measurement data of course must also be validated, processed and communicated according to best (scientific) practices. Only then does the participation of citizens make sense, and can we speak of citizen science par excellence.

For that matter, it’s nice to note that the research into air quality through citizen science also immediately puts the spotlight on the importance of science and technology in tackling social problems. This will inspire young people to choose a STEM (science, technology, engineering, mathematics) course of studies, since the social relevance of STEM is so strongly emphasised.

Who are the polluters?

In the case of air pollution, the question ‘Who or what is the source?’ cannot be answered unambiguously. Point sources such as the chimneys of companies and houses, and the exhausts of vehicles are known, as are the emissions of ammonia by the cattle breeding industry. But the atmosphere is of course a dynamic whole. The spread of pollutants depends heavily on the weather, with political boundaries playing no role. In addition, chemical reactions take place in the atmosphere that can form or remove pollutants.

When looking for the source of air pollution, we would do well to make a distinction between the different pollutants. It then becomes apparent that there is no clear link between general air quality and the individual types of sources. In the case of sulphur dioxide (SO2), for example, the emissions come mainly from heavy industry in the Antwerp and Ghent ports, and from some isolated industrial sites in the Kempen region of Limburg.

The map with the concentrations of nitrogen dioxide (NO2) immediately gives a completely different picture. In addition to the expected industrial hotspots, the urban agglomerations in Antwerp, Ghent and (the northern edge of) Brussels are particularly noteworthy. Moreover, most major cities are also exhibiting increased concentrations, as are the motorways and even the smaller traffic arteries.  According to the latest insights, the European standards for NO2 would even be exceeded in street canyons in small and medium-sized municipalities. Need it also be said that road traffic is responsible for much of the nitrogen oxide emissions, and then mainly diesel engines?

The concentrations of ammonia (NH3) again give a completely different picture. The vast majority of these emissions come from the cattle breeding industry, more specifically from animal manure and fertilisers. It is not without reason that there are hotspots in West Flanders and in the north of the provinces of Antwerp and Limburg, regions that are known for intensive livestock farming.

In the case of particulate matter (PM10, PM2.5, soot, and ultrafine particles), the link with the sources is much less clear. Roughly speaking, we can state that the heating of buildings (including wood stoves) is the largest direct source of particulate matter in Flanders. In addition, industry, traffic,agriculture and horticulture also play a significant role.

The distinction between primary and secondary particulate matter is important. Particulate matter can be blown directly into the air: think of soot particles from diesel engines, or PM10 from wood stoves or from the wear and tear of roads and vehicles. But they can also be formed secondarily from atmospheric gases.

Due to the wide range of source types, the concentration of particulate matter in Flanders is generally more uniformly distributed than other pollutants. But here too the annual averages are somewhat higher in the Antwerp and Ghent port areas and the densely populated regions of Flanders – with peaks with low concentrations near the coast and in Limburg.

There are two things to note about this. First, much of the particulate matter in Flanders comes from abroad. According to some estimates, three-quarters of the total quantity of particulate matter in Flemish air is imported – to which of course it should be added that Flanders also exports particulate matter. Second, the different types of particulate matter may have a different impact on health. Yet, the standards are determined on the basis of the total mass of the particulate matter mix. For some years, the European limit values for particulate matter have not been exceeded in Flanders. However, if we compare the results against the WHO health standard (10 μg/m³ for PM2.5) then large parts of Flanders do not comply and it is clear that further measures are needed. This once again shows the different levels at which the problem of air pollution plays out: from local to regional and even to global. And therefore at which of the different policy levels measures can be taken to improve air quality.

Air and climate: Two sides of the same coin

An ideal environmental policy includes measures that are conducive to air quality (everywhere) and to the fight against global warming. After all, the presence of a link between the climate and air quality should not come as a surprise. However, this link is complex. Thus, sulphur dioxide is known to reflect sunlight, which causes the gas to have a cooling effect, but at the same time it can cause serious environmental and health damage: think of acid rain and toxic sulphur vapours respectively. The removal of diesel vehicles from the fleet since “dieselgate” is having a favourable impact on local air quality due to reduced emissions of NOx and black carbon (BC). The latter is regarded as one of the most harmful components of particulate matter.

Thus reducing BC also benefits the climate: BC after all is an important greenhouse gas component. A clear win-win for air and climate. However, promotion of this elimination of diesel (at least in the short term) is resulting in a shift to petrol cars. Due to their increased CO2 emissions, we note here a negative impact on the climate. Total replacement of all diesel passenger cars with petrol variants would result in a halving of the NOx and BC emissions in Flanders, but CO2 emissions would increase by 10 %. This is the paradox that presents itself for policy, but also for the individual citizen who wants to buy a new car now.

Electric cars are currently in pole position to reduce emissions from road traffic. But here too the problem of air quality does not automatically disappear. An electric car is on average heavier than a petrol or diesel car, as a result of which the emission of particulate matter via the tyres will be relatively higher. Against this of course is the fact that the electric car has no exhaust emissions. And even if it does not run 100 % on renewable electricity, it is better for the air quality that the NOx and soot are emitted by a single controllable power plant than diffused through the exhaust of many cars.

Ozone: a particular matter

Ozone is a strange phenomenon. It is not emitted directly and is only formed in the atmosphere, especially on warm, sunny days. Ozone concentrations often peak at locations where the concentration of other pollutants is lower. Ozone after all is formed from chemical precursors such as nitrogen dioxide and volatile organic compounds, but at high concentrations of nitric oxide – close to (traffic) sources – ozone is also partly broken down.

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