(503a) Characterizing Aerosol Liquid Water at Two Contrasting Locations in the Eastern and Western United States

Aerosol liquid water (ALW) is an important component of the atmosphere as it is widely present in ample concentrations, and it could thus promote the formation of particles in the aqueous phase. This study characterizes ALW in two cities of contrasting metrological conditions and source emissions influences in the United States. A climatology of ALW was derived based upon ten years of aerosol composition measurements at an urban site in Maryland and a remote site in Colorado, in the eastern and western United States, respectively. Annual organic aerosol concentrations and inorganic speciation were provided by the Maryland Department of the Environment in the east and a combination of filter collection from Colorado State University and IMPROVE were used in the west. ALW associated with inorganic components (W_inorg) was simulated using the ISORROPIAv2.1 aerosol thermodynamic model, while the liquid water associated with organics (W_org) was calculated according to Koehler theory. The total ALW was quantified as the sum of W_inorg and W_org content. ALW was correlated to sulfate concentrations in the eastern United States (R² = 0.45), however, it was tightly correlated to nitrate concentrations in the west (R² = 0.60). Despite average ALW concentrations of 6 µg m^-3 observed in the east throughout the year, concentrations in the west were dependent on the season. Summertime ALW concentrations were higher (average = 1.4 µg m^-3) compared to lower wintertime concentrations (average = 0.4 µg m^-3) in the west, mainly due to the abundance of W_org. In the cold seasons, the contribution of W_org was 10% and 20% of the total ALW in the west and east, respectively. On the other hand, the contribution of W_org in the warm seasons was 40% in the east and 70% in the west, possibly due to biogenic emissions and wildfires in the two locations, respectively. This work demonstrates the importance of accounting for organic-associated water. Effects of these organic concentrations on pH will further be examined. Additionally, an analysis of ALW will be presented from other locations in the United States to examine the spatial distribution of ALW concentrations.