Hygroscopic growth study in the framework of EARLINET during the SLOPE I campaign: synergy of remote sensing and in situ instrumentation

Abstract

Abstract. This study focuses on the analysis of aerosol hygroscopic growth during the Sierra Nevada Lidar AerOsol Profiling Experiment (SLOPE I) campaign by using the synergy of active and passive remote sensors at the ACTRIS Granada station and in situ instrumentation at a mountain station (Sierra Nevada, SNS). To this end, a methodology based on simultaneous measurements of aerosol profiles from an EARLINET multi-wavelength Raman lidar (RL) and relative humidity (RH) profiles obtained from a multi-instrumental approach is used. This approach is based on the combination of calibrated water vapor mixing ratio (r) profiles from RL and continuous temperature profiles from a microwave radiometer (MWR) for obtaining RH profiles with a reasonable vertical and temporal resolution. This methodology is validated against the traditional one that uses RH from colocated radiosounding (RS) measurements, obtaining differences in the hygroscopic growth parameter (γ ) lower than 5 % between the methodology based on RS and the one presented here. Additionally, during the SLOPE I campaign the remote sensing methodology used for aerosol hygroscopic growth studies has been checked against Mie calculations of aerosol hygroscopic growth using in situ measurements of particle number size distribution and submicron chemical composition measured at SNS. The hygroscopic case observed during SLOPE I showed an increase in the particle backscatter coefficient at 355 and 532 nm with relative humidity (RH ranged between 78 and 98 %), but also a decrease in the backscatter-related Ångström exponent (AE) and particle linear depolarization ratio (PLDR), indicating that the particles became larger and more spherical due to hygroscopic processes. Vertical and horizontal wind analysis is performed by means of a co-located Doppler lidar system, in order to evaluate the horizontal and vertical dynamics of the air masses. Finally, the Hänel parameterizaPublished by Copernicus Publications on behalf of the European Geosciences Union. 7002A. E. Bedoya-Velásquez et al.: Hygroscopic growth study in the framework of the SLOPE I campaign tion is applied to experimental data for both stations, and we found good agreement on γ measured with remote sensing (γ 532 = 0.48 ± 0.01 and γ 355 = 0.40 ± 0.01) with respect to the values calculated using Mie theory (γ 532 = 0.53 ± 0.02 and γ 355 = 0.45 ± 0.02), with relative differences between measurements and simulations lower than 9 % at 532 nm and 11 % at 355 nm.

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

“…As shown in Figure 4 and Table 2, both are generally constant within each layer of each case, indicating uniformly atmospheric mixing and vertical homogeneity in both cases. Therefore, the hygroscopic growth that occurred in both cases, resulting in changes in aerosol optical properties, was most likely caused by the uptake of water [54,55]. When the aerosol layer is uniformly mixed, the variation of aerosol optical properties with height can be considered mainly caused by water uptake in the aerosol layer.…”

Aerosol hygroscopic growth, contributing factors and impact on haze events in a severely polluted region in northern China

“…The aerosol hygroscopic 17 optical enhancement factor [ ] has also also been employed, defined as the ratio between value under dry conditions (Kotchenruther et al, 1999). It can be measured by a humidified 21 tandem nephelometer (e.g., Covert et al, 1972;Feingold and Morley, 2003;Titos et al, 2018).…”

“…TDMA and nephelometer (Bedoya-Velásquez et al, 2018). Raman lidar systems also provide 14 measurements at higher spatial and temporal resolutions which are useful for examining the 15 effects of aerosol hygroscopic growth on pollution events (e.g., Y.-F. Wang et al, 201216 Su et al, 2017).…”

Reply to Ref #2

“…(b) Optical microscopic images of a particle which contained (NH 4 ) 2 SO 4 and 1,2,6-trihydroxyhexane with a mass ratio of 1 : 2.1, during an experiment in which temperature was kept at around 291 K, while RH was decreased. Reprint with permission by Bertram et al (2011). of supporting substrates (including TEM grid, Parafilm-M, aluminum foil, Ag foil, silicon wafer and cover glass) on hygroscopicity measurements using optical microscopy and concluded that TEM grids were the most suitable substrate for this application. Optical microscopy was also used to study hygroscopic properties of MgCl 2 and NaCl−MgCl 2 mixed particles (Gupta et al, 2015), and hygroscopic properties (including DRH and growth factors) of these particles were found to differ significantly from NaCl.…”