Three authors (Gavin Sun, Glen Hazlewood, and Cheryl Barnabe) independently completed title and abstract and full-text reviews. Studies were included based on the following criteria: assessing the outcome of a rheumatic disease of interest (RA, JIA, SARDs, and individual diseases of autoimmune myositis, SLE, scleroderma, and vasculitis), individual exposure to ambient air pollutants (PM2.5, PM10, SO2, NO2, CO, and O3), and having a case-control, case cross-over, or cohort design. Only English language studies were included. The study had to report risk estimates (any of relative risk (RR), hazard ratio (HR), or odds ratio (OR)) with the corresponding 95% confidence intervals (95% CI) or sufficient data for calculation. Reviews, case reports, mechanism studies, and nonhuman studies were excluded.