Retrieval of Aerosol Size Distributions From In Situ Particle Counter Measurements: Instrument Counting Efficiency and Comparisons With Satellite Measurements

Abstract

The method to derive aerosol size distributions from in situ stratospheric measurements from the University of Wyoming is modified to include an explicit counting efficiency function (CEF) to describe the channel‐dependent instrument counting efficiency. This is motivated by Kovilakam and Deshler's (2015, https://doi.org/10.1002/2015JD023303) discovery of an error in the calibration method applied to the optical particle counter (OPC40) developed in the late 1980s and used from 1991 to 2012. The method can be applied to other optical aerosol instruments for which counting efficiencies have been measured. The CEF employed is the integral of the Gaussian distribution representing the instrument response at any one aerosol channel, the aerosol counting efficiency. Results using the CEF are compared to previous derivations of aerosol size distributions (Deshler et al., 2003, https://doi.org/10.1029/2002JD002514) applied to the measurements before and after Kovilakam and Deshler's correction of number concentration for the OPC40 calibration error. The CEF method is found, without any tuning parameter, to reproduce or improve upon the Kovilakam and Deshler's results, thus accounting for the calibration error without any external comparisons other than the laboratory determined counting efficiency at each aerosol channel. Moments of the new aerosol size distributions compare well with aerosol extinctions measured by Stratospheric Aerosol and Gas Experiment II and Halogen Occultation Experiment in the volcanic period 1991–1996, generally within ±40%, the precision of OPC40 moments, and in the nonvolcanic period after 1996, generally within ±20%. Stratospheric Aerosol and Gas Experiment II and Halogen Occultation Experiment estimates of aerosol surface area are generally in agreement with those derived using the new CEF method.

The ATAL within the 2017 Asian Monsoon Anticyclone: Microphysical aerosol properties derived from aircraft-borne in situ measurements

“…For this purpose we chose two measurements conducted with a balloon-borne set-up which continues the series of in situ data described in Deshler et al (2003), Ward et al (2014), andDeshler et al (2019). The comparison measurements were from Hyderabad (India) in August 2015, also during the ASM period, and from Laramie (United States of America) in August 2013.…”

Comparison of Coincident Optical Particle Counter and Lidar Measurements of Polar Stratospheric Clouds Above McMurdo (77.85°S, 166.67°E) From 1994 to 1999

“…Including this counting efficiency function into the measurement description led to a revision of the method to derive uni/bimodal lognormal size distributions from the OPC measurements. These revisions have now been applied to all the measurements and lead to a significant improvement in the agreement of OPC derived extinctions, from fitted size distributions, with satellite measured extinctions (Deshler et al., 2019). The corrections of the OPC measurements for particle evaporation and counting efficiency have been applied to all the OPC measurements presented here.…”

“…While Kovilakam and Deshler suggested an algorithm to correct the OPC aerosol concentrations for this calibration error, this algorithm was never implemented. Instead a more fundamental approach to correct for the calibration error was developed by Deshler et al (2019). Deshler and coworkers reanalyzed the laboratory measurements of Kovilakam and Deshler, implementing several further refinements of the measurements, and came to the conclusion that the proper way to correct for the calibration error, was not by correcting the number concentration, but by adjusting the size of each channel boundary to be at the 50% counting efficiency point which is assumed of all OPCs.…”

Improved tropospheric and stratospheric sulfur cycle in the aerosol–chemistry–climate model SOCOL-AERv2

“…Lana et al (2011) updated the marine DMS dataset to include three times as many DMS measurements as the previous dataset (Kettle et al, 1999;Kettle and Andreae, 2000) used by Sheng et al (2015). Transient degassing volcanic SO 2 emissions were taken from Diehl et al (2012). To represent eruptive emissions, we applied a satellite-derived dataset from Carn et al (2016).…”