How will air quality, weather and climate improve because of the containment, social distancing and lockdown during the COVID-19 outbreak?
This is a topic of almost continual discussion in the South China Morning Post, scmp.com , an English language newspaper in Hong Kong. This is both because air quality is a major problem in China (but one to which they are paying a good deal of attention) and because massive economic interruptions are relatively frequent. The Olympics were a big one, national festivals like Spring Festival, 春节, Chūn jié, give readers a chance to mourn or hope, the current trade war modulates the scale of industry, and now we have Covid-19.

Obviously the virus crisis is bringing about great improvement in current air quality almost everywhere. I doubt that any climatic effects are known yet.

Here's an article which introduces the topic in China -- which is, after all, the major live experiment going on: https://www.scmp.com/news/china/society/article/3044747/beijings-air-quality-shows-significant-improvements-war