Light source effects on aerosol photoacoustic spectroscopy measurements

Abstract

Photoacoustic spectroscopy measurements of flame-generated soot aerosol coated with small amounts of water yielded absorption enhancements that were dependent on the laser used: quasi-continuous wave (Q-CW, ≈ 650 ps pulse duration and 78 MHz repetition rate) versus continuous wave (CW). Water coating thickness was controlled by exposing the aerosol to a set relative humidity (RH). At ≈ 85 % RH, the mass of the soot particles increased by an amount comparable to a monolayer of water being deposited and enhanced the measured absorption by 36 % and 15 % for the Q-CW and CW lasers, respectively. Extinction measurements were also performed using a cavity ring-down spectrometer (extinction equals the sum of absorption and scattering) with a CW laser and negligible enhancement was observed at all RH. These findings demonstrate that source choice can impact measurements of aerosols with volatile coatings and that the absorption enhancements at high RH previously measured by Radney and Zangmeister (2015) [1] are the result of laser source used (Q-CW) and not from an increase in the particle absorption cross section.

High‐sensitivity detection and quantification of CHCl3 vapors in various gas environments based on the photoacoustic spectroscopy

“…This faint signal of He is due to its small vibrational‐transitional excitation cross section, thermodynamic, and acoustic properties of He in PA cell. This result for CHCl 3 is in agreement with the results for other gases such as SO 2 , SF 6 , and NO 2 . In other words, the mechanism of PA signal generation depends on the molecular and atomic mass, density, and total pressure (mixture of species and buffer gas).…”

“…17 Because of the advantages of this method, after Alexander Graham Bell, this method was developed by various scientists such as Kreuaer 18 ; Viengerov 19 (in order to detect by IR source with high noise); Schafer et al 20 (in order to increase the quality factor of PA cells); Kerr and Atwood 21 (in order to measure the absorption spectrum of water vapor); Bernegger and Sigrist 22 (performed PA spectroscopy of gases and vapors for trace gas analysis); Besson et al 23,24 (provided PA spectroscopy setup by diode laser in order to detect CH 4 and HCl); Gondal and Yamani 25 (for ozone detection); Lima et al 26 (for high-sensitivity detection of 16 ppb ethylene and 42 ppb ammonia); Kumar et al 27,28 (to trace hazardous chemicals by Quantum cascade lasers (QCLs)); Mohebbifar et al 29 and Dibaee et al 30 (in order to obtain high-sensitive spectroscopy of SO 2 , NO 2 , and SF 6 ); Yufei Ma 31 and Yufei Ma et al 32 (for ppb-level detection of ammonia based on QEPAS); and so forth. [33][34][35][36] The PA spectroscopy is based on the absorption of light by the gas. The gas molecules that are exposed to electromagnetic wave are excited to a higher rotational, vibrational, or electronic quantum state.…”

“…This result for CHCl 3 is in agreement with the results for other gases such as SO 2 , SF 6 , and NO 2 . 34,35 In other words, the mechanism of PA signal generation depends on the molecular and atomic mass, density, and total pressure (mixture of species and buffer gas). In fact, part of the energy likely converts to the undesired radiative deactivations particularly at low pressures leading to reduce the PA signal.…”

Comparing aerosol refractive indices retrieved from full distribution and size- and mass-selected measurements

“…To ensure sizing accuracy, the DMA was calibrated using polystyrene nanospheres with nominal (actual) diameters of 50 (50 ± 2) nm, 60 (57 ± 4) nm, 100 (102 ± 3) nm, 150 (147 ± 3) nm, 200 (203 ± 5) nm, 240 (240 ± 5) mn, 500 (457 ± 10) nm and 700 (701 ± 6) nm. For all measurements, the relative humidity inside the DMA was monitored to ensure it was stable (< 10 %) for the duration of an experiment to minimize hygroscopic water uptake and evaporation and/or condensation related interferences from particle bound water in the photoacoustic spectrometer [54–57].…”

Simultaneous transmission and absorption photometry of carbon-black absorption from drop-cast particle-laden filters

“…However, Arnott et al (2003) compared an aethalometer and PSAP with a PAS and found a decrease in absorption with the PAS with increased relative humidity (beyond 70%), while the PSAP had an erratic response. This decrease in the measured PAS signal was attributed to preferential evaporation of water from the particles (Radney and Zangmeister 2017; Langridge et al 2013; Murphy 2009; Lewis et al 2009). Differences in the chemical composition of aerosolized carbonaceous particles and other light-absorbing non-carbon-based particle types have also made it difficult to evaluate aerosol absorption characteristics (Bond et al 2013).…”