How can cities detect, and avoid, peaks in particulate-matter air pollution?

Pollution over Lyon. Image: Getty.

In January 2017, France and a large part of Europe were struck by episodes of particulate matter pollution. These microscopic particles are known as PM2.5 and PM10 when they measure less than 2.5 or 10 micrometers (µm) in diameter respectively. The Conversation

They are proven to be harmful to human health because they enter our respiratory system, and the smallest can even enter our blood flow. According to the European Environment Agency, air pollution is the cause of 467,000 premature deaths annually in Europe.

These particles can come from natural sources (sea salt, volcanic eruptions, forest fires, etc.) or human activities (transport, heating, industry, etc.)

What is a pollution peak?

Pollution peaks occur when regulatory warning thresholds, as defined in 2008 by the European Union and transposed to French law in late 2010, are exceeded. In virtue of these regulations, the first level of severity (known as the “public information and warning threshold”) is reached for PM10 particles when there are ≥50 µg per cubic meter of air (m³) in the atmosphere; the warning level is reached at ≥80 µg/m³.

There is no trigger limit for PM2.5, but just a set maximum amount of 25 µg/m³ on average per year.

However, these regulations have serious limitations. The “mass” concentration thresholds which indicate the total mass of particles in the air and which are used to assess the danger of particulate matter pollution are higher than the levels recommended by the WHO; the latter have been set for PM10 at 20 µg/m³ on average per year and 50 µg/m³ on average per day, in order to take account of chronic and short-term exposure.

In addition, the only parameter taken into account in European and French regulations concerns mass concentration. The concentration in terms of number (i.e. the number of particles per m³ of air), and the chemical composition are not taken into account for the triggering of warnings.

Lastly, there are no regulations for very small particulate matter (less than 1 µm), which is mainly produced by human activity, even though it is potentially the most harmful.

Comparison of the size of microscopic particles with a hair and grain of sand. Image: EPA/creative commons.

How are they detected?

In France, the Ministry for the Environment has delegated the task of monitoring air quality and regulated pollutants across the country to certified associations united under Fédération Atmo France. They are supported in this task by the Central Laboratory for the Monitoring of Air Quality.

These associations put in place automatic measurements for the concentration of pollutants, as well as other monitoring measures to allow a better understanding of the phenomena observed, such as the chemical composition of particles, or weather conditions.

These measurements can be combined with approaches for modeling particle concentration, thanks in particular to Prevair, the French forecast platform. Calculating the history of air mass can also be used to reveal the origin of particles, and it is therefore now possible to describe the phenomena at the origin of the increase in concentrations in relative detail.

Explanation of a real case

The graph below, produced from observations by our research department and measurements by Atmo Hauts-de-France, illustrates an example of pollution peaks that affected the local area in January 2017.

During this period, anticyclonic weather conditions contributed to the stagnation of air masses above pollutant-emitting areas. In addition, cooler temperatures led to an increase in emissions (notably linked to domestic wood heating) and the formation of “secondary” particles which formed after chemical reactions in the atmosphere.

Image: Data V. Riffault/SAGE (Cappa and Climibio projects)/creative commons.

The graphs show changes in mass concentrations of PM10 and PM2.5 over a period of several days at the Lille Fives monitoring station, as well as changes in several chemical species measured in PM1 4 km away on the University of Lille campus.

We can see that almost all the particles fell within the PM2.5 proportion, something which rules out natural phenomena such as a dust being blown in from deserts, since such particles mainly fall within the range of 2.5 to 10 µm. Furthermore, the particles in question are generally smaller in size than 1 µm.

The pollution episode began on the evening of 21 January  and continued throughout the weekend, in spite of a lower level of road traffic. This can be explained by an increase in wood burning (as suggested by the m/z 60 tracer, which is a fragment of levoglucosan, a molecule emitted by pyrolysis of cellulose found in wood).

Wood burning and other forms of combustion (such as traffic or certain industries) also emit nitrogen dioxide (NO2) as a gas, which can turn into nitric acid (HNO3) through a reaction with hydroxyl radicals (•OH) in the atmosphere.

At sufficiently low temperatures, HNO3 combines with ammonia (NH3) produced by farming activity to form ammonium nitrate (NH4NO3) solid. These are known as “secondary particles”.

A slight decrease in concentrations of particulate matter was observed at the end of the weekend, with more favorable weather conditions for the dispersion and elimination of pollutants.

In this episode, the very low concentrations of sulfates rule out an impact from coal power stations in Germany and Eastern Europe. It is therefore definitely a question of local and regional pollution linked to human activity and which accumulated as a result of unfavorable weather conditions.


How can this be avoided?

Since we cannot control the weather conditions, levers of action are primarily based on reducing pollutant emissions.

For example, reducing the formation of secondary particles will entail limiting NO2emissions linked to road traffic through road space rationing measures; for NH3 emissions, action must be taken regarding farming practices (spreading and rearing methods).

Concerning emissions from wood heating, replacing older devices with cleaner ones will enable better burning and fewer particulate matter emissions; this could be accompanied by an investment in housing insulation.

But these measures should not make us forget populations’ chronic exposure to concentrations of particulate matter which exceed the recommended WHO thresholds. This type of pollution is insidious and is damaging to health in the medium and long term, notably with the development of cardio-vascular and respiratory diseases and lung cancer.

Véronique Riffault is professor of atmospheric science at IMT Lille Douai – Institut Mines-Télécom.

This article was originally published on The Conversation. Read the original article.

 
 
 
 

Here are eight thoughts on TfL’s proposed cuts to London’s bus network

A number 12 bus crosses Westminster Bridge. Image: Getty.

In 2016, the urbanism blog City Observatory had a modest proposal for how American cities could sort out their transport systems: “Londonize”.

Its theory, the name of which referenced another popular urbanism blog, Copenhagenize, was that the key plank of Transport for London’s success was something that even transport nerds did not consider very sexy: its buses.

Though the Tube might get more glamorous press, London’s bus service really is impressively massive: It carries roughly 2.3bn passengers per year—much more than the Tube (1.3bn), close to the New York City subway (2.8bn), and nearly half as much as every bus service in America combined (5.1bn), while serving a population roughly 1/35 as large.

How has TfL done this? By making its bus network high frequency, reliable, relatively easy to understand and comprehensive. We rarely talk about this, because the tube map is far more fun – but the reason it’s so difficult to fall off the transport network in Greater London is because you’re never that far from a bus.

Given all that, we should probably talk about TfL’s plans to rethink – and in most cases, cut – as many as 36 different central London bus services over the next few months.

I’m not going to rehash details of the changes on which TfL is consulting from next month: there are just too many of them, and anyway it’s someone else’s scoop. The story was originally broken by Darryl Chamberlain over on 853 London; there’s also some fascinating analysis on Diamond Geezer’s blog. You should read both of those stories, though preferably not before you’ve finished reading this one.

Before offering my own analysis of the proposed changes, though, I should offer a few examples. More than a dozen routes are facing a trim: the 59 from King’s Cross back to Euston, the 113 from Oxford Circle to Marble Arch, the 171 from Holborn all the way down to Elephant & Castle and so on. A couple – the 10, the 48, the C2, and at most times the special routemaster version of the 15 – are being withdrawn altogether.

On, and one new route is planned – the 311, from Fulham Broadway to Oxford Circus. This will help plug some of the cuts to the 11, 19 and 22.

So, what does all this mean? Some thoughts:

1) This might not quite be as awful as it initially sounds

TfL says that demand for buses has fallen by around 10 per cent in London in recent years. It predicts it’ll fall further when Crossrail opens, as passengers switch to the new line, or to the tube routes relieved by the new line. So: the idea of taking some unwanted capacity out of the system is not, in itself, terrible.

Striping out unnecessary buses should also improve air quality in some of London’s worst pollution hot spots, and improve traffic flow, hopefully speeding up journeys on those buses that remain. 

A map from the presentation in which TfL explained its plans, showing the reduction in bus numbers on key arteries. Hilariously, notes Darryl Chamberlain, “It no longer produces its own maps, so has had to use one prepared by a bus enthusiast”.

The plans might even free up buses and staff to increase frequencies in outer London where demand hasn’t fallen – though these plans won’t be unveiled until next year and, for reasons I’ll come to below, I’ll believe it when we see it.

2) For many bus users, a lot of these changes will pass almost unnoticed

By my count, I use nine of the affected routes with any regularity – but only three of the changes are things that I’m likely to be at all inconvenienced by. Most of the changes either affect a part of the route I don’t take, or one where there are easy, and pain free alternatives.

This is anecdotal, obviously – perhaps I’m just lucky. But my suspicion is that a lot of these changes will go unnoticed by most passengers. It’s only the sheer number of them happening at once that makes this look like a big deal.

3) The Hopper fare makes this easier...

Once upon a time, if you had to switch buses, you had to pay a second fare. This isn’t true of journeys on the tube or railways – and since bus passengers have, on average, less money than tube passengers, it amounted to a pretty unfair tax on poorer Londoners.

But in January, in what is probably his most notable policy achievement of his two years in office so far, London’s mayor Sadiq Khan changed the rules. Now you can take as many buses as you want within an hour, for a single fare: that means you can switch buses without paying a penalty.

That will have made it easier for TfL to cut routes back: replacing a direct bus journey with one that requires a change no longer means imposing a financial penalty on passengers.


4) ...but not that easy

That’s about where the good news stops, though – because there are reasons other than cost why people prefer direct bus routes. Needing to change buses will be difficult for anyone with any form of mobility impairment, for example. Even for those of us lucky enough not to fall into that category, it’ll be annoying: it’s just easier to stay in one seat for 40 minutes than to get turfed off and have to fight for a new one halfway through.

More than that, from the passengers’ point of view, excess capacity feels quite good a lot of the time: it means your bus may well be nice and empty. Reducing the number of buses along those key corridors will also make those that remain more crowded.

5) The motive is almost certainly financial

Another of Sadiq Khan’s big policy promises was to freeze fares. He made this promise at a time when central government is massively reducing the financial support it gives TfL (the work, Chamberlain notes, of Evening Standard editor George Osborne, back when he was chancellor). And the Hopper fare, while a great idea in many ways, means a further reduction in income.

So: TfL is scrambling for cash: this is why I remain cynical about those new outer London bus routes. I would be amazed if money wasn’t a motivation here, not least because...

6) TfL thinks no one will notice

Any attempt to reduce tube frequencies, let alone close a station, would result in uproar. Hashtag campaigners! Angry people pointing at things in local newspapers! Damning reports on the front of the Evening Standard from the bloke who made it happen!

Buses, though? Their routes change, slightly, all the time. And do you really notice whether your local route comes every 10 minutes or every 12? That’s not to mention the fact that bus passengers, as previously noted, tend to be poorer – and so, less vocal – than tube passengers.

So cuts, and the savings they bring, are much easier to sneak through. TfL probably would have gotten away with it, too, if it hadn’t been for those meddling bloggers.

Although...

7) Scrapping the C2 might be a mistake

The C2 runs from Parliament Hill, through Kentish Town and Camden to Oxford Circus. In other words, it links north London, where a lot of journalists live, to the offices of the BBC and Buzzfeed.

As occasional New Statesman writer James Ball notes, this is probably not the easiest route to quietly shelve.

8) None of this is set in stone

The consultation doesn’t even begin until next month and then will run for six weeks – so all these plans may yet be forgotten. We shall see.

Anyway – here’s Darryl Chamberlain’s original scoop, and here’s some detailed analysis on Diamond Geezer. Please support your local bloggers by reading them.

Jonn Elledge is the editor of CityMetric. He is on Twitter as @jonnelledge and on Facebook as JonnElledgeWrites.

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