Indirect Effects of Secondary Organic Aerosol on Cirrus Clouds

Abstract

Secondary organic aerosols (SOA) have been identified as a potential source of depositional ice nucleating particles and thus may have a radiative effect on cirrus clouds. This study develops a global model to examine the radiative effect of SOA on cirrus clouds using different treatments for the size distribution of SOA. The SOA from new particle formation by organics and their subsequent growth has a radiative effect of 0.35 ± 0.06 W m−2, while the radiative effect of SOA calculated by assuming a fixed size distribution is 0.31 ± 0.08 W m−2. This positive radiative effect on cirrus clouds opposes the negative effect of anthropogenic soot on cirrus clouds. In addition, the inclusion of SOA as an ice nucleating particle changes the background ice crystal number concentration, which impacts the calculation of radiative forcing from other aerosols. The radiative forcing of aircraft soot is estimated to be −0.11 ± 0.03 W m−2 when including SOA formed from new particle formation by organics and growth. This is less negative than simulations that do not include ice nucleation from SOA. The change in SOA formed from organic nucleation from the preindustrial period to the present day causes a positive forcing of 0.02 ± 0.04 W m−2. It is important to use a size distribution based on the explicit formation mechanism for SOA to calculate their radiative effects. The simulation using an assumed fixed size distribution incorrectly results in a negative forcing of SOA between the present day and preindustrial atmospheres because it does not correctly calculate the change of SOA in the accumulation mode.

Radiative forcing of anthropogenic aerosols on cirrus clouds using a hybrid ice nucleation scheme

“…The nucleated SOA particles grow by deposition and coagulation of sulfuric acid as well as the oxidation products of isoprene, α-pinene, limonene, and aromatics, which are in the aerosol phase. This SOA was simulated using the version of the CESM/IMPACT model outlined in Zhu et al (2017 and Penner (2019, 2020). The SOA that meets the requirements of the glass transition temperature and RH i calculated using the equations in Wang et al (2012) acts as an effective heterogeneous INP.…”

Decreased Aviation Leads to Increased Ice Crystal Number and a Positive Radiative Effect in Cirrus Clouds

“…This results in approximately 0.6% of all emitted aircraft soot that can possibly acting as an INP to form ice. The model's ability to simulate the profile of soot from fossil fuel, biofuel and aircraft emissions was evaluated by comparison with field campaigns (Figure 2 in Samset et al., 2014; Figure S15 in Zhu & Penner, 2020a). Dust and sea salt are each carried in four separate bins with varying radii.…”

Snow particles physiochemistry: feedback on air quality, climate change, and human health

“…Consequently, BC shows less dependence on wavelength, strongly absorbing light from UV to near infrared. However, AAE of BrC varies from smaller than 1 to as great as 8, 230 indicating high wavelength dependence. As a result, the absorption of BrC sharply decreases with increasing wavelength, with strong absorption on UV but weak absorption on short-wavelength visible light.…”

“…The following absorption measurement by UV-vis spectrophotometer cannot reect the contribution from insoluble BrC. For modeling methods, currently, the mass concentration of BrC is estimated by using a certain percentage of organic carbon, 229,230 which no doubt would cause deviation in the radiative impacts of BrC.…”