Impact of aerosol hygroscopic growth on retrieving aerosol extinction coefficient profiles from elastic-backscatter lidar signals

Abstract

Abstract. Light detection and ranging (lidar) measurements have been widely used to profile the ambient aerosol extinction coefficient (σ ext ). The particle extinction-to-backscatter ratio (lidar ratio, LR), which strongly depends on the aerosol dry particle number size distribution (PNSD) and aerosol hygroscopicity, is introduced to retrieve the σ ext profile from elastic-backscatter lidar signals. Conventionally, a constant column-integrated LR that is estimated from aerosol optical depth is used by the retrieving algorithms. In this paper, the influences of aerosol PNSD, aerosol hygroscopic growth and relative humidity (RH) profiles on the variation in LR are investigated based on the datasets from field measurements in the North China Plain (NCP). Results show that LR has an enhancement factor of 2.2 when RH reaches 92 %. Simulation results indicate that both the magnitude and vertical structures of the σ ext profiles by using the column-related LR method are significantly biased from the original σ ext profile. The relative bias, which is mainly influenced by RH and PNSD, can reach up to 40 % when RH at the top of the mixed layer is above 90 %. A new algorithm for retrieving σ ext profiles and a new scheme of LR enhancement factor by RH in the NCP are proposed in this study. The relative bias between the σ ext profile retrieved with this new algorithm and the ideal true value is reduced to below 13 %.

Hygroscopicity of Different Types of Aerosol Particles: Case Studies Using Multi-Instrument Data in Megacity Beijing, China

“…Table 4 summarizes the fitting results, and Figure 5 shows the f β (RH, λ) and the fitting results for each case. The Case II hygroscopic growth factor was much stronger than that of Case I. β in Case I increased 1.4 times [ f β−caseI (86%)] in the RH range of 65-86%, while β in Case II increased 3.1 times [ f β−caseII (86%)] in the same RH range, similar to the increase reported in previous studies for other regions [22,23,41,42,54]. Both of the parameters b from the Kasten model and γ from the Hänel model indicate the strength of hygroscopicity.…”

“…While there have existed many studies on aerosol hygroscopicity using in situ and laboratory observation data, there have been relatively few studies in open atmospheric environment conditions in China whose aerosols are heavy and complex with significant impact on regional climate and environment [3,19]. With the increasing amount of lidar measurements, attempts have been made to derive the hygroscopicity of atmospheric aerosols under certain atmospheric conditions [20][21][22][23][24].…”

Method to measure the size-resolved real part of aerosol refractive index using differential mobility analyzer in tandem with single-particle soot photometer

“…It is surrounded by two main streets: Zhongguancun North Street to the west and Chengfu Road to the south. This site can provide representative information on the urban roadside aerosols (Zhao et al, 2018).…”

“…The core diameters flow the lognormal distribution with the mean core diameter of 120 nm (Raatikainen et al, 2017). When calculating the scattering strength, the complex refractive index of the core 1.8 + 0.54i (Zhao et al, 2018) is used. The complex refractive of the shell adopts the measured mean values (1.46 + 0i) during the field measurements.…”

Towards continuous monitoring of aerosol hygroscopicity by Raman lidar measurements at the EARLINET station of Payerne

“…The main limitation to address these studies comes from the difficulty to obtain RH profiles with high vertical and temporal resolution. Most of the studies carried out so far have used sensors to measure RH on board of RS or aircrafts or in meteorological towers in combination with the aerosol measurements from lidars to investigate the aerosol hygroscopicty (Wulfmeyer and Feingold, 2000;Veselovskii et al, 2009;Granados-Muñoz et al, 2015;Haeffelin et al, 2016;Lv et al, 2017;Zhao et al, 2017;Fernández 5 et al, 2018). Recently, the combination of temperature profiles from microwave radiometers (MWR) and water vapour mixing ratio (r) profiles from Raman lidar have been used to retrieve RH profiles (Navas-Guzmán et al, 2014) and applied to aerosol hygroscopic studies (Bedoya-Velásquez et al, 2018).…”