This is the result of left joining filtered/cleaned asthma hospitalization and PM2.5 concentration data. I then grouped the boroughs and year together to make things look less messy. Afterwards I summarized the averages for both hospitalizations and PM2.5 concentrations.

# A tibble: 5 × 2
  Borough       correlation
  <chr>               <dbl>
1 Bronx               0.979
2 Brooklyn            0.947
3 Manhattan           0.974
4 Queens              0.964
5 Staten Island       0.949

There is a correlation between the PM2.5 concentration and asthma hospitalization rates. Though Brooklyn actually has the highest population the Bronx consistently had the highest correlation between the two (based on annual, summer, and winter data!). The regression we saw earlier also reinforces the fact that for every time the PM2.5 concentration increases by 1, the hospitalization rate generally increases by 4.88 per 10,000 people. It should be kept in mind that there is an abundance of variables that could also contribute to the asthma-related hospitalization rate.