Coronavirus travels on air pollution - many studies

Covid patients exposed to higher pollution levels ‘hospitalised for longer,’ says study June 2023 Telegraph
- Download the PDF from VitaminDWiki
A Literature Review of the Effects of Air Pollution on COVID-19 Health Outcomes Worldwide: Statistical Challenges and Data Visualization Jan 2023 FREE PDF
The impact of air pollution on COVID-19 incidence, severity, and mortality: A systematic review of studies in Europe and North America - 2022 FREE PDF
Links between air pollution and COVID-19 in England - Jan 2021 FREE PDF
Positive association between outdoor air pollution and the incidence and severity of COVID-19. A review of the recent scientific evidences - Jan 2022 FREE PDF
Air pollution can increase the threat posed by COVID-19 Feb 2022
Long-term exposure to air pollution and COVID-19 incidence: a prospective study of residents in the city of Varese, Northern Italy BMJ Feb 2022 PDF

Fact: Pollution reduces the amount of time that people are outdoors
Fact: Pollution is often associated with hot temperatures - another reason to not go outdoors
Fact: Less time outdoors results in lower Vitamin D levels
Fact: Pollution attenuates the amount of UVB getting to the skin (but by only a few percent)
Fact:The body's ability to fight Irritation/Inflammation is aided by vitamin D
Fact: All of the types of PM2.5 deaths are also associated with low vitamin D
Most air pollutions reduce Vitamin D (PM2.5 is worst) – June 2021
Observation: Vitamin D should improve the health of people in dusty or polluted air

There were 60+ references in Air Pollution reduces Vitamin D page as of June 2023
Inhaled vitamin D might turn out to be especially good form as it goes directly to the lungs.