There are particularly large decreases in Sulphur Dioxide and Carbon Monoxide - the former due to reduced sulphur in fuel, and the latter due to catalytic converters. But pretty much all the other metrics have continued to improve too. Having worked in Bloomsbury for 30 years, I can definitely tell it's got better.
But it's not good enough. When City Hall is hailing that air quality is actually legal for the first time in ten years, that's both good and comical at the same time.
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. Certainly I have less problem with allergies in London than I had in Berkeley. This should in no way excuse London, but you have to get things in perspective.
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.
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.
If you're above the acceptable limit, and you don't reduce exposure to below that limit, then there's no benefit.
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:
I think that any move to an area with a sufficiently different mix of pollen can cause problems for your immune system.
I suspect simply because there isn't as much nature in the vicinity, which I don't actually appreciate. Oh well.
You need to convert units, because the US readings are given on the AQI scale, whereas the London ones are raw measurements:
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.
This is common among people that move from one region to any other region.
I'm allergic to grass but not tree pollen or mold spores.