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It’s worth saying the average pollution levels are not capturing the full health impacts. You could easily have a spike along roads due to diesel but at the same time a reduction in the average, because roads are only one of the emission sources. But they are where people spend a lot of their time, in cars and buses in traffic, walking, cycling; and nearby many people are living, and going to shops and cafes. A lot of the effects of pollution are hyper local.

To add to this, cumulative improvements in air quality over time don't mean squat if your current levels are still considered harmful.

If you reduce your exposure to lead by 50% annually and you're still well above the safe exposure limit, you might be making progress and still not having positive impacts on health.

There isn't a magical threshold where things flip from "harmful" to "not harmful" and it doesn't matter how far above the harmful line you are. Reducing your exposure to lead by 50% annually will have big positive health impacts even if it's still too high.

Actually there are limits for how much lead is considered harmful in your system. OSHA has exposure limits that indicate amounts per hour, and those amounts decrease the longer you're exposed. It takes a long time for lead to leave your system and prolonged exposure at levels higher than your system can process will result in a net gain or build up.

If you're above the acceptable limit, and you don't reduce exposure to below that limit, then there's no benefit.

OSHA picking an acceptable limit does not mean that the harm when below that limit is zero, or that harm does not increase as you go higher above that limit. Being exposed to ten times the limit is worse than being exposed to twice the limit.

Yes - it’s local to the point that air quality can vary significantly within a matter of feet along large or congested roads and walking closer to buildings/further from the road in these areas is a surprisingly simple thing you can do to improve the quality of air you breath.

Or indoors, for that matter. It's very easy for a house to reach 50 to 100 on an AQM meter, which isn't going to be immediately noticeable, but which very well could have long-term consequences.

A good HEPA filter will take care of that. As a bonus, if you're allergic, you'll get rid of most of the pollen that way.

>>it's clear that London's air quality has steadily improved over time:

That's not what the data you linked show, though. You charted Sulphur Dioxide only, but when you look at say PM2.5, there's not even data for the whole period (09/1993-09/2019):

>>Warning: Valid PM2.5 Particulate measurements are available for only 37% of the requested period.

This means they've got data on <10 years, out of the 26 years in the period.

At least for some pollutants that are widely studied and linked to mortality and negative health outcomes - such as PM2.5, PM10, NO2, there does not seem to be an "improvement", based on these data:

https://www.londonair.org.uk/london/asp/advgraphssiteplot.as...

London is the only city in world that turns everyone's snot black, not even Delhi or Beijing does that.

I’ve lived in London for 15 years and I’ve never experienced that. I suspect it’s something of an urban myth.

Happens to me! It's mostly the tube I think though - airborne brake residue etc, is what I've been told.

Me too, in the tube – definitely not a myth. A friend even got his white dress shirt ruined by the stuff.

That’s credible - it could be quite localised on the tube to certain stations or lines if that is the case - I’ve noticed that I get black marks all over my hands occasionally from the escalator handrail in some stations but it’s only a small minority of the ones I’ve been to.

Damn, how much would it cost to just run some air filters down there?

'merican here with normal snot; when I'm doing stuff (house fixy stuff) that turns my mucous colors, it's my sign that I need to go grab a dust mask. Is this not really a concern down there in the underground because $REASONS, or one of those "umm, never thought about it, but now that you mention it..." things?

It's more: this is how we have to get to work so go back to your book :D

Used to happen to me in New York 15 years ago. Hasn't happened since, though.

Happened to me systematically in Wuhan, a few times (but much less) in Shanghai

Beijing and Shenzhen both made my snot go black when I was there sourcing LED components.

To play a devil advocate, there could be a lot of non-human allergens, with a most common culprit being pollen.

Especially in the Bay Area. There's a reason sour dough bread is a thing, for example. It's in the air.

Wild yeast is in the air everywhere. Sourdough is a thing in SF not because the environment there is particularly good for it, but because of historical reasons (ie, French bakers moving in during the gold rush).

>Wild yeast is in the air everywhere

But not the same yeast everywhere. Plus bacteria are also a factor, and also vary place to place. Some may cause worse allergies than others, depending on the person.

As far as I know, French bakers didn't bring the yeast (or starter) responsible for sourdough. They just brought french bread. The sourdough part happened naturally, at least initially. Now it's actively encouraged.

But even with the right starter, the further east you go, the harder good sourdough is to make.

Pollen could definitely be a key part of it, but I doubt it's the whole story. Checking the PM 2.5 count for yesterday for the Bloomsbury sensor in central London, it's actually about 70% of that at any of the sensors in the East Bay (Berkeley, Oakland, etc) or San Francisco.

http://www.baaqmd.gov/about-air-quality/current-air-quality/...

You need to convert units, because the US readings are given on the AQI scale, whereas the London ones are raw measurements:

https://aqicn.org/calculator/

As someone who made the opposite move (Bay Area -> London) I found that I started suffering from hay fever for the first time in my life.

I think that any move to an area with a sufficiently different mix of pollen can cause problems for your immune system.

As someone who has always lived in London, I started getting hayfever around age 22. When asked by doctors if I have any allergies, and I say nothing except maybe hayfever, they always say "oh everyone has hayfever"

Its commonly not allergy e.g. not a histamine response. It can be simple irritation due to particulates in the air. Everybody should respond to that.

Some years ago I moved from northern Norway to central Dublin. By any reckoning that's a decrease in air quality -- though Dublin is still much better than most cities -- but it also came with a reduction in allergic reactions.

I suspect simply because there isn't as much nature in the vicinity, which I don't actually appreciate. Oh well.

> As an aside, I moved from London to the Bay Area for a number of years. Many of the Londoners I knew who moved there developed terrible allergies after a few years.

This is common among people that move from one region to any other region.

Do you know any specifics of why the Bay area is worse than London? Or what causes it?

The bay area has a lot of grass and pollen producing trees. And also mold spores in the rainy season. South bay has a lot of grass. Berkeley has a lot of tree pollen. San Francisco tends to have issues with mold spores.

I'm allergic to grass but not tree pollen or mold spores.