Indoor aerosols in the absence of strong sources are generally of outdoor origin.  Once in the indoor environment these aerosols can undergo rapid changes in relative humidity and temperature when transiting through ventilation systems that alternatively heat or cool depending on outdoor conditions.  Rapid decreases in temperature and subsequent increases in relative humidity during air conditioning activate particles to droplets with subsequent transition back to a sub-saturated regime on short time scales; akin to cloud cycling of outdoor aerosols.  Additionally, there will be significant surface wetting in the HVAC which removes water soluble species from the gas-phase and can impact equilibration of semi-volatile species.   High time resolution observations of aerosol composition outdoors and indoors using aerosol mass spectrometry was used to probe aerosol composition in both a university classroom and test house.  These measurements provide detailed observational insights of the impact of aerosol water on the chemical composition of indoor aerosol particles.  For example, residual cigarette smoke can contribute significant mass to indoor aerosols via reactive uptake into an acidic aqueous phase.  Semi-volatile inorganic and organic species in the aerosol phase are also impacted by the presence of water in the HVAC system with both ammonium nitrate and oxidized organic species in the aerosol exhibit mass loss in excess of expected losses from filtration.  This occurs even when the temperature gradient indoors would favor additional temperature driven partitioning of semi-volatile species to the particle phase (i.e. cooler indoors than outdoors).  <br/>

Modulation of aerosol water content of indoor aerosols and impact on partitioning of water soluble species

2019 Fall National Meeting

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