Abstract
Abstract. The study of aerosol optical properties is essential to understand its impact on the global climate. In our recent field measurement carried out in the Gehu area of southwest Changzhou City, a photoacoustic extinctiometer (PAX) and a cavity attenuated phase shift albedo monitor (CAPS-ALB) were used for online aerosol optical properties measurement. Laboratory calibration with gas and particle samples were carried out to correct disagreements of field measurements. During particle calibration, we adopted ammonium sulfate (AS) samples for scattering calibration of nephelometer parts of both the instruments, then combined these with number-size distribution measurements in the MIE model for calculating the value of the total scattering (extinction) coefficient. During gas calibration, we employed high concentrations of NO2 for absorption calibration of the PAX resonator and then further intercompared the extinction coefficient of CAPS-ALB with a cavity-enhanced spectrometer. The correction coefficient obtained from the laboratory calibration experiments was employed on the optical properties observed in the field measurements correspondingly and showed good results in comparison with reconstructed extinction from the IMPROVE model. The intercomparison of the calibrated optical properties of PAX and CAPS-ALB in field measurements was in good agreement with slopes of 1.052, 1.024 and 1.046 for extinction, scattering and absorption respectively, which shows the reliability of measurement results and verifies the correlation between the photoacoustic and the cavity attenuated phase shift instruments.
Highlights
Atmospheric aerosols can directly affect the earth’s energy balance and cause global temperature changes by absorbing and scattering solar radiation (Horvath, 1993; Haywood and Shine, 1995; Penner et al, 2001)
In our calibration experiments for photoacoustic extinctiometer (PAX), with an assumption of linearity in calibration down to the detection limit of the instruments (Arnott et al, 2000), the high concentration of absorbing gas and scattering particles generated a huge absorption and scattering effect that weakened the interference of noise and corrected the response curve of the PAX photoacoustic resonator and nephelometer respectively
The calibration result showed that the absorption measurement of PAX only needs slight correction and has high accuracy
Summary
Atmospheric aerosols can directly affect the earth’s energy balance and cause global temperature changes by absorbing and scattering solar radiation (Horvath, 1993; Haywood and Shine, 1995; Penner et al, 2001). Considerable studies were undertaken to investigate the optical properties of aerosol particles from different regions (Baynard et al, 2007; Petzold et al, 2013; Moosmüller et al, 1998). The optical properties of regional aerosols depend on particle size distribution, mixing state and complex refractive index; online measurements are necessary (Nakayama et al, 2015; Schwartz et al, 2010). The calibration of instruments is a key step to ensure the reliability and quality of online measurement data of aerosol optical properties. Integrating nephelometry (IN) is an effective, economical and widely recognized method for obtaining aerosol scattering coefficients online (Beuttell and Brewer, 1949; Heintzenberg and Charlson, 1996; Abu-Rahmah et al, 2006). On the systematic limitations of this technique were noted; i.e., the so-called truncation error made it technically impossible to cover the full range of the scattering angle and was mainly studied through numerical simulations with a Mie model
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