Comparison of in situ and columnar aerosol spectral measurements during TexAQS-GoMACCS 2006: testing parameterizations for estimating aerosol fine mode properties

Abstract

Abstract. During the 2006 Texas Air Quality Study and Gulf of Mexico Atmospheric Composition and Climate Study (TexAQS-GoMACCS 2006), the optical, chemical and microphysical properties of atmospheric aerosols were measured on multiple mobile platforms and at ground based stations. In situ measurements of the aerosol light extinction coefficient (σ ep ) were performed by two multi-wavelength cavity ring-down (CRD) instruments, one located on board the NOAA R/V Ronald H. Brown (RHB) and the other located at the University of Houston, Moody Tower (UHMT). An AERONET sunphotometer was also located at the UHMT to measure the columnar aerosol optical depth (AOD). The σ ep data were used to extract the extinctionÅngström exponent (å ep ), a measure of the wavelength dependence of σ ep . There was general agreement between theå ep (and to a lesser degree σ ep ) measurements by the two spatially separated CRD instruments during multi-day periods, suggesting a regional scale consistency of the sampled aerosols. Two spectral models are applied to the σ ep and AOD data to extract the fine mode fraction of extinction (η) and the fine mode effective radius (R eff,f ). These two parameters are robust measures of the fine mode contribution to total extinction and the fine mode size distribution, respectively. The results of the analysis are compared to R eff,f values extracted using AERONET V2 retrievals and calculated from in situ particle size meaCorrespondence to: D. B. Atkinson (atkinsond@pdx.edu) surements on the RHB and at UHMT. During a time period when fine mode aerosols dominated the extinction over a large area extending from Houston/Galveston Bay and out into the Gulf of Mexico, the various methods for obtaining R eff,f agree qualitatively (showing the same temporal trend) and quantitatively (pooled standard deviation = 28 nm).

Aerosol Light Extinction Measurements by Cavity Attenuated Phase Shift (CAPS) Spectroscopy: Laboratory Validation and Field Deployment of a Compact Aerosol Particle Extinction Monitor

“…The importance of measuring theÅ parameter is known; in addition, the potential use of in situ measurements ofÅ to quantify the column fine mode fraction of atmospheric aerosols has been emphasized recently (Atkinson et al 2009). Overall, the use of the CAPS monitor for the direct measurement of σ ep would benefit ground-monitoring networks where aerosol light extinction is typically calculated from the sum of scattering and absorption measurements obtained using commercial nephelometers and PSAPs, respectively.…”

Comment on "Classification of aerosol properties derived from AERONET direct sun data" by Gobbi et al. (2007)

“…(3) above (O'Neill et al, 2001b(O'Neill et al, ,2003. The validation of ρ eff,f retrievals from SDA outputs is the objective of current investigations (Atkinson et al, 2010).…”

Using spectral methods to obtain particle size information from optical data: applications to measurements from CARES 2010

“…This section provides a qualitative description of the fine-and coarse-mode AOD (or extinction) retrieval algorithm (SDA, or spectral deconvolution algorithm) and fine-mode optical sizing (FMC, or fine-mode curvature) method developed by O'Neill. The details of the derivation and application of the SDA are provided in previous publications (O'Neill et al, 2003;Atkinson et al, 2010;Kaku et al, 2014). The MAT-LAB code that implements the approach is available from O'Neill upon request.…”

“…Current applications of the method start by fitting ln(b ext ) (or ln(b scat ) or ln(AOD)) versus ln(λ) to a second-order polynomial, where b ext is the measured wavelength-dependent extinction coefficient (see Atkinson et al, 2010 andKaku et al, 2014 for scattering and extinction coefficient applications, Saha et al, 2010 for a Sun photometry AOD application and Baibakov et al, 2015 for a star photometry AOD application). The extinction and its first and second derivatives are determined from the fit at a reference wavelength of 500 nm, a common reference wavelength along with 550 nm in optical studies.…”

“…Beyond adding to the utility of the in situ optical measurements, this provides an opportunity to test the methods against other, complementary measures of particle size and size-dependent scattering and extinction. For example, Atkinson et al (2010) used the approach of O'Neill et al (2003) to analyze in situ, three-wavelength aerosol extinction measurements made during the 2006 TexAQS II campaign near Houston, TX. More recently, Kaku et al (2014) showed, for a range of marine atmospheres, that the application of this spectral approach to obtain FMF from threewavelength scattering coefficient measurements was largely coherent with the submicron fraction (SMF) of scattering, obtained from scattering coefficient measurements of the fine-and coarse-mode components using impactor-based separation of the aerosol.…”