Cloud albedo increase from carbonaceous aerosol

Abstract

Abstract. Airborne measurements from two consecutive days, analysed with the aid of an aerosol-adiabatic cloud parcel model, are used to study the effect of carbonaceous aerosol particles on the reflectivity of sunlight by water clouds. The measurements, including aerosol chemistry, aerosol microphysics, cloud microphysics, cloud gust velocities and cloud light extinction, were made below, in and above stratocumulus over the northwest Atlantic Ocean. On the first day, the history of the below-cloud fine particle aerosol was marine and the fine particle sulphate and organic carbon mass concentrations measured at cloud base were 2.4 µg m −3 and 0.9 µg m −3 respectively. On the second day, the below-cloud aerosol was continentally influenced and the fine particle sulphate and organic carbon mass concentrations were 2.3 µg m −3 and 2.6 µg m −3 respectively. Over the range 0.06-0.8 µm diameter, the shapes of the below-cloud size distributions were similar on both days and the number concentrations were approximately a factor of two higher on the second day. The cloud droplet number concentrations (CDNC) on the second day were approximately three times higher than the CDNC measured on the first day. Using the parcel model to separate the influence of the differences in gust velocities, we estimate from the vertically integrated cloud light scattering measurements a 6% increase in the cloud albedo principally due to the increase in the carbonaceous components on the second day. Assuming no additional absorption by this aerosol, a 6% albedo increase translates to a local daytime radiative cooling of ∼ 12 W m −2 . This reCorrespondence to: W. R. Leaitch (richard.leaitch@ec.gc.ca) sult provides observational evidence that the role of anthropogenic carbonaceous components in the cloud albedo effect can be much larger than that of anthropogenic sulphate, as some global simulations have indicated.

Atmospheric Research Over the Western North Atlantic Ocean Region and North American East Coast: A Review of Past Work and Challenges Ahead

“…They had suggested that one explanation could have been that the mechanism for SOA formation was more efficient than assumed. Leaitch et al (2010) conducted flights in October 2003 off the Nova Scotia coast as part of the Canadian Surface Ocean-Lower Atmosphere Study (SOLAS). This was an important study as it was perhaps the first airborne effort up until that time to probe ACI.…”

“…With regard to past WNAO studies of how aerosols affect clouds, two airborne investigations as part of NARE (Leaitch et al, 1996) and SOLAS (Leaitch et al, 2010) specifically focused on N d and controlling factors such as degree of turbulence and abundance of carbonaceous aerosol. Medina et al (2007) conducted a surface-based CCN closure study at the Thompson Farm AIRMAP site in New Hampshire and concluded that size-resolved chemical data and treatment of mixing state are helpful for more successful closure.…”

Assessment of cloud condensation nucleus activation of urban aerosol particles with different hygroscopicity and the application to the cloud parcel model

“…These studies have investigated the influences of aerosol physical properties (number concentration and size distribution), chemical properties (chemical composition and hygroscopicity), and the above mentioned effects of organics on cloud properties (cloud droplet number concentration and indirect radiative forcing). Some studies have shown that the influences of chemical properties of aerosol particles and the effects of organics on the cloud activation are particularly significant in polluted environments [Lance et al, 2004;Leaitch et al, 2010]. In contrast, other studies have shown that the effects of aerosol physical properties are important and that the effects of chemical properties and organics are small [Fountoukis et al, 2007;Reutter et al, 2009].…”

Factors influencing the microphysics and radiative properties of liquid-dominated Arctic clouds: Insight from observations of aerosol and clouds during ISDAC

“…The size distribution and chemical composition of aerosol particles are the preeminent factors dictating CCN ability. The relative importance of these factors is not clear, as previous studies have demonstrated both size and composition as the predominant factors controlling CCN ability [ Dusek et al , 2006; Leaitch et al , 2010; Quinn et al , 2008; Zelenyuk et al , 2010]. The mixing state of aerosol can also play a role; however, the distinction between internally and externally mixed particles as CCN becomes less significant if particles are sufficiently hygroscopic [ Wang et al , 2010].…”