Development of a Flow Tube to Investigate Aerosol Yield Using Environmentally Relevant Ammonia and Humidity Conditions

Following the discovery that sulphur dioxide (SO2) and nitrogen oxides (NOx) cause acid rain, Canada (and other industrialized countries) dramatically reduced the emissions of both chemicals. While these acidic precursor emissions have been decreasing, the emissions of ammonia, a base, have not been controlled. This has led to the ammonia/ammonium (NH3/NH4+) conjugate base pair becoming a dominant pH buffer in the atmospheric aqueous phase including cloud droplets and fine particulate matter (PM2.5). Consequently, NH3/NH4+ will directly modulate gas-particle partitioning and, in turn, secondary organic aerosol (SOA) formation. Properly understanding these mechanisms is critical for understanding and mitigating the negative health and climate effects of atmospheric particles. The RH-dependent impacts of NH3 on the phase partitioning of organics will be investigated through the development and use of a flow tube system, that can perturb ambient air or the reaction products from chamber experiments. The air passing through (or bypassing) the flow tube will be analyzed with an array of online and offline instruments, including an Ultra-High Sensitivity Aerosol Spectrometer and Ion Chromatography. Initial development of the flow tube has focused on size-dependent transmission efficiency of particles through the flow tube; determining the range of relative humidity (RH) conditions possible; developing protocols for offline filter and denuder sampling. Once the flow tube is developed, studies can be performed to provide insight into how NH3 and relative humidity impact the gas-particle partitioning of organic acids under a range of conditions. This knowledge can then be used to better predict the climate and health effects of aerosols in the atmosphere.