Source : nasa
Researchers have discovered how black carbon evolves from hydrophobic particles to cloud nucleation sites, possibly eliminate the heat absorbing particles from the sky as per the research published on JGR Atmospheres.
There is a stubborn heat-absorbing particle floating in Earth’s atmosphere – it doesn’t like water, it absorbs light and takes its time to move on. Black carbon in the atmosphere tends to linger until it absorbs enough water to fall from sky. During this time, black carbon absorbs energy from the sun & heats-up the surrounding air, creating a radiative effect.
New, youthful black carbon tends to be water resistant. Over time, particles age & become more hygroscopic, or able to absorb water from air. But when black carbon begins to absorb water, act like cloud nuclei & eliminated itself from the atmosphere?
Researchers have previously studied the hygroscopic conditions of black carbon in laboratory, with limited conditions on chemical sources & water vapor conditions. In all of these studies, cloud nucleation values of black carbon were in-direct measurements.
In a new study by Hu et al., Researchers simultaneously measured the concentration of cloud condensation nuclei & black carbon particles. The sampling site was near heavily traffic-ked roads & industrial centers in Wuhan, China, an urban mega-city in center of the country. .
They first corrected the particle size, then measured the cloud condensation nuclei & individual black carbon particles at certain levels of water supersaturation in the atmosphere. The team found that activation diameter, or the size of black carbon particle in which half of the particles will nucleate & precipitate-out, was 144 ± 21 nanometers at 0.2% supersaturation. The team found that activation diameter, or the size of black carbon particle in which half of the particles will nucleate & precipitate-out, was 144 ± 21 nanometers at 0.2% supersaturation.
In addition, the team found that a particle itself can affect the size of nucleation. For example, the amount of organic content in a particle or any coating on black carbon can alter the hygroscopicity & therefore the activation.
The research team noted that their work may help improve estimates of longevity of black carbon particles suspended in the atmosphere & therefore the radiative impacts these particles can have.
