AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Ambient Aerosol Extinction in Great Smoky Mountains National Park
TIM GORDON, Jim Renfro, Anthony Prenni, Gavin McMeeking, Ping Chen, Handix Scientific
Abstract Number: 372 Working Group: Aerosol Physics
Abstract Light scattering and extinction are fundamental properties of visibility. To quantify extinction the IMPROVE (Interagency Monitoring of Protected Visual Environments) program, which is tasked with monitoring visibility in U.S. National Parks and Wilderness Areas, relies primarily on reconstructions from speciated aerosol (filter) measurements and humidification growth factors (among other parameters). Under many atmospheric conditions reconstructed extinctions compare favorably with measurements; however, at high relative humidities (RH) aerosol-induced light extinction is very sensitive to RH perturbations, and technical challenges (e.g., inlet losses and truncation errors) have thwarted previous efforts to quantify it (extinction) with closed-path instruments. Thus under such conditions not only are the uncertainty bounds large for the humidification growth factors used to reconstruct extinction (and therefore visibility), but also it has not even been possible to provide robust in situ measurements for comparing these reconstructions against.
The Open-Path Cavity Ringdown Spectrometer (OPCRDS) was designed to overcome the RH limitations of previous extinction instruments. The OPCRDS was recently deployed in the Great Smoky Mountains National Park (GSM), where the high RH and high photochemical activity typical in summer provided an opportunity to explore the upper limits of the aerosol hygroscopicity (f(RH)) curve and the accuracy of the IMPROVE extinction reconstruction algorithm. True ambient extinction measured by the OPCRDS and dry extinction measured by a traditional closed-cell extinction monitor were used to investigate the hygroscopicity of aerosol at GSM and the importance of coarse-mode particles to light extinction. In addition, extinction obtained with the OPCRDS was used to validate the reconstructed extinction currently reported by IMPROVE. We also discuss the broader implications of these data for radiative transfer simulations in remote sensing and climate forcing research.