Funds from this grant support the work of chemists Paul Ziemann and Jose-Luis Jimenez of the University of Colorado Boulder to improve our fundamental scientific understanding of the basic chemistry of aerosols in indoor environments. Using state-of-the-art instrumentation and methodology, Ziemann and Jimenez will measure the chemical composition of unperturbed and aged gases, aerosol particles, and surfaces in two to three homes and buildings; conduct laboratory studies of gases, aerosols, and surface films formed from reactions of organic chemicals commonly found in indoor air and on human occupants with O3 and NO3 radicals, water, and acids; and begin to develop theoretical models that explain these chemical reactions.Because environmental chemistry to date has focused virtually exclusively on the reactions taking place outdoors, the supported research fills a lacuna in our scientific understanding of the world.