NOS2 and asthma: We hypothesized that exposure to PM2.5 and V, assessed by residential measures integrated over 6 days, repeated 6 months later, would be associated with changes in buccal cell DNA methylation of targeted CpG loci in the promoter region of several asthma inflammatory genes (e.g., interleukin 4 (IL4), interferon gamma (IFNγ), NOS2A and arginase2 (ARG2)) among urban African American and Dominican children.