Fog‐ and cloud‐induced aerosol modification observed by the Aerosol Robotic Network (AERONET)

Abstract

[1] Large fine mode-dominated aerosols (submicron radius) in size distributions retrieved from the Aerosol Robotic Network (AERONET) have been observed after fog or low-altitude cloud dissipation events. These column-integrated size distributions have been obtained at several sites in many regions of the world, typically after evaporation of low-altitude cloud such as stratocumulus or fog. Retrievals with cloud-processed aerosol are sometimes bimodal in the accumulation mode with the larger-size mode often $0.4-0.5 mm radius (volume distribution); the smaller mode, typically $0.12 to $0.20 mm, may be interstitial aerosol that were not modified by incorporation in droplets and/or aerosol that are less hygroscopic in nature. Bimodal accumulation mode size distributions have often been observed from in situ measurements of aerosols that have interacted with clouds, and AERONET size distribution retrievals made after dissipation of cloud or fog are in good agreement with particle sizes measured by in situ techniques for cloud-processed aerosols. Aerosols of this type and large size range (in lower concentrations) may also be formed by cloud processing in partly cloudy conditions and may contribute to the "shoulder" of larger-size particles in the accumulation mode retrievals, especially in regions where sulfate and other soluble aerosol are a significant component of the total aerosol composition. Observed trends of increasing aerosol optical depth (AOD) as fine mode radius increased suggests higher AOD in the near-cloud environment and higher overall AOD than typically obtained from remote sensing owing to bias toward sampling at low cloud fraction.

Observing and understanding the Southeast Asian aerosol system by remote sensing: An initial review and analysis for the Seven Southeast Asian Studies (7SEAS) program

“…The development around Hanoi also makes the site heavily influenced by local pollution as well. Haze has been known to develop in the region, leading to large particle sizes in the Oct-Nov period (Eck et al, 2012). The Bac Lieu site to the south of Ho Chi Minh City is considerably cleaner.…”

Column aerosol optical properties and aerosol radiative forcing during a serious haze-fog month over North China Plain in 2013 based on ground-based sunphotometer measurements

“…These hygroscopic compositions could be one of the major reasons for the trimodal size distribution during the most intense haze period from 10 to 16 January. Another possible reason of the bimode submicron size distribution could be related to the haze-fog and cloud processing Eck et al, 2012). The smaller mode (0.12 to 0.20 micron meter) may be interstitial aerosol that were not modified by incorporation in droplets and/or aerosol that are less hygroscopic in nature.…”

Long-term variability of aerosol optical thickness in Eastern Europe over 2001–2014 according to the measurements at the Moscow MSU MO AERONET site with additional cloud and NO<sub>2</sub> correction

“…However, several recent studies indicated that clouds can have a real impact on AOT. These mechanisms of aerosolcloud interaction include aerosol hygroscopic growth, increasing aerosol concentration due to air convergence, and new particles formation in the presence of clouds (Su et al, 2008;Jeong and Li, 2010;Eck et al, 2012Eck et al, , 2014. In addition to the well-known process of hygroscopic particle growth, there is a mechanism of the gas-to-particle conversion that occurs more intensively in the aqueous phase in cloud droplets due to the oxidation of gases (SO 2 , NO x , SOA) (Eck et al, 2014).…”