Ortega Amber, Shingler Taylor, Crosbie Ewan, Wonaschütz Anna, Froyd Karl, Gao Ru-Shan, Schwarz Joshua, Perring Anne, Beyersdorf Andreas, Ziemba Luke, Jimenez Jose, Jost Pedro Campuzano, Wisthaler Armin, Russell Lynn, Sorooshian Armin
Department of Chemical and Environmental Engineering, University of Arizona, Tucson, AZ, USA.
NASA Langley Research Center, Hampton, VA, USA.
J Geophys Res Atmos. 2016 Nov 27;121(22):661-677. doi: 10.1002/2016JD025471. Epub 2016 Nov 7.
This study reports on the first set of ambient observations of sub-1.0 hygroscopicity values (i.e., growth factor, ratio of humidified-to-dry diameter, and (RH), ratio of humidified-to-dry scattering coefficients, less than 1) with consistency across different instruments, regions, and platforms. We utilized data from (i) a shipboard humidified tandem differential mobility analyzer (HTDMA) during Eastern Pacific Emitted Aerosol Cloud Experiment (E-PEACE) in 2011, (ii) multiple instruments on the DC-8 aircraft during Studies of Emissions, Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEACRS) in 2013, as well as (iii) the Differential Aerosol Sizing and Hygroscopicity Spectrometer Probe (DASH-SP) during measurement intensives during Summer 2014 and Winter 2015 in Tucson, Arizona. Sub-1.0 s were observed across the range of relative humidity (RH) investigated (75-95%), and did not show a RH-dependent trend in value below 1.0 or frequency of occurrence. A commonality between suppressed hygroscopicity in these experiments, including sub-1.0 , was the presence of smoke. Evidence of externally mixed aerosol, and thus multiple s, was observed during smoke periods resulting in at least one mode with < 1. Time periods during which the DASH-SP detected externally mixed aerosol coincide with sub-1.0 (RH) observations. Mechanisms responsible for sub-1.0 hygroscopicity are discussed and include refractive index (RI) modifications due to aqueous processing, particle restructuring, and volatilization effects. To further investigate ambient observations of sub-1.0 s, (RH), and particle restructuring, modifying hygroscopicity instruments with pre-humidification modules is recommended.
本研究报告了首批关于低于1.0的吸湿性值（即生长因子、湿直径与干直径之比、以及湿散射系数与干散射系数之比，小于1）的环境观测结果，这些观测在不同仪器、区域和平台间具有一致性。我们利用了以下数据：（i）2011年东太平洋排放气溶胶云实验（E-PEACE）期间船上的加湿串联差分 mobility分析仪（HTDMA）；（ii）2013年区域调查排放、大气成分、云和气候耦合研究（SEACRS）期间DC-8飞机上的多台仪器；以及（iii）2014年夏季和2015年冬季在亚利桑那州图森进行测量密集期时的差分气溶胶粒径和吸湿性光谱仪探头（DASH-SP）。在所研究的相对湿度（RH）范围（75 - 95%）内均观测到低于1.0的值，且在低于1.0的值或出现频率方面未呈现出与RH相关的趋势。这些实验中吸湿性受到抑制（包括低于1.0的值）的一个共同特点是存在烟雾。在烟雾期观察到了外部混合气溶胶的证据，因此存在多个值，导致至少有一个模式的值小于1。DASH-SP检测到外部混合气溶胶的时间段与低于1.0（RH）的观测结果一致。文中讨论了导致低于1.0的吸湿性的机制，包括由于水相处理、颗粒重构和挥发效应引起的折射率（RI）变化。为了进一步研究低于1.0的值、（RH）以及颗粒重构的环境观测情况，建议使用预加湿模块对吸湿性仪器进行改进。
