Thirdhand smoke (THS) consists of residual tobacco smoke pollutants that 1) remain on surfaces, in dust (including in walls, carpets, pillows, clothes), (2) are remitted back into the gas-phase from reservoirs where they accumulated, and (3) react with oxidants and other compounds in the environment to yield secondary pollutants. THS deposits and accumulates in all indoor environments where tobacco has been smoked. THS includes many of the same compounds found in freshly emitted tobacco smoke as well as new carcinogens. Drs. Quintana and Matt will characterize THS pollutants and their persistence over time in real-world samples collected from the home environments of former smokers to better understand the potential health threat posed by THS. The study is being conducted in collaboration with the UCSF Graduate School of Public Health.