Photoacoustic spectroscopy accurately measures atmospheric 12CO2 and 13CO2 concentrations and optical properties of carbonaceous aerosols

Understanding of today's climate and predictions of future climate require accurate input data to model the energy balance between the sun's irradiance and Earth’s atmosphere, oceans, land, and surface ice. An important driver of climate change is the absorption and scattering of sunlight by carbon-based aerosols (soot, smoke, etc) that have widely-varying, source-dependent, and history-dependent optical properties. We use a resonant photoacoustic spectrometer (PAS) to measure the optical absorption cross-section of various carbonaceous aerosols that we generate and characterize in situ. The photoacoustic signal is directly proportional to the energy absorbed by the particles. When combined with simultaneous measurements of the total extinction using cavity ring-down spectroscopy, we obtain the particles’ wavelength-dependent albedo (fraction of incident light scattered). Another important driver of climate change is atmospheric carbon dioxide, a greenhouse gas. With the remarkable linearity, sensitivity,...