This study will focus on evaluating the short-term benefits of a common portable air purifier technology in reducing air pollutant exposure and the anticipated concomitant health impacts. High ambient levels of various air pollutants in the Shanghai area serve as a useful model to test the portable air purifier intervention in a realistic setting. As most people using a portable air purifier would only be able to do so in their residences, the investigators have designed our study only to test residential air purifier use. Our hypothesis is that the reduction in pollutant concentrations in indoor air caused by the air purifier will result in measurable reductions in risk factors for cardiovascular and respiratory diseases.