Summer’s almost always a lot better in Taipei - I guess it’s related to winds from the south rather than the north. The serious pollution in Taipei starts to kick in around this time of year, continuing until April or so.
Last year Taipei’s pollution seemed especially bad to me, but the big caveat is that it was the first winter I’d added an AQI index app to my phone, so I always knew what the pollution count was. So maybe it wasn’t actually worse - I was just more aware of it.
Perhaps somewhere in the thread linked to below there’s a numerical record of changes over the years, but at the moment I can’t find one.
EDIT: Looking back at another thread, I see that I used to have the sense that winter was bad but not awful - the only awful times were the spring dust storms. But last winter, if I recall correctly, situation was so bad through the winter that the dust storms didn’t really make much of a difference.