Are the exercise equipment in the park suitable for exercising for health?

I stopped working out at the gym a year ago and have been using exercise equipment in the park. Since working out at the gym is an indoor exercise, I felt that the air quality was not good, so I decided that working out in a clean place in the park would be good for my health. Now, about a year later, I want to get my opinion again. Since there are only four or five exercise machines in the park, I am suspicious that it is not possible to get the desired effect from working out. What is the reality? I am curious about that.