Research News
1. Global mortality from ambient PM2.5 exposure
Evidence of premature mortality attributable to ambient PM2.5 exposure continues to grow. In a recent study, Apte et al. (2015) have estimated global premature mortality from ambient PM2.5 exposure using high resolution satellite-derived PM2.5 and integrated concentration-response function to cover widely varying demography. Main focus of the study is to understand the mitigation measure implication. It was found that a modest improvement in relatively clean areas (e.g. North America and Europe) would result in large avoided premature mortality, while a substantial effort is required in the polluted regions (e.g. China and India). Average PM2.5 would need to decrease by 20-30% over the next 15 years just to maintain present day premature mortality rate. The study also highlights the complexity involved in mitigation measures. For example, population exposure benefit per unit emission control is very high in densely populated countries like India. There is a need to carry out region-specific study to comprehend the problem and reduce the uncertainty in burden of disease.
Reference: Apte, J. S., J. D. Marshall, A. J. Cohen and M. Brauer (2015): Addressing global mortality from ambient PM2.5, Environmental Science and Technology, DOI:10.1021/acs.est.Sb0123.
2. Evidence of invigoration of aerosol-limited warm clouds
Invigoration effect is the most elusive and debated among all aerosol-cloud interactions. Earlier studies have found evidence of invigoration in deep convective clouds with cold top and warm base. This study demonstrated the effect to be evident on warm clouds in the pristine (aerosol optical depth, AOD is less than 0.2) regions of the world. Significant increase in rain rate and cloud fraction and a decrease in cloud top pressure was observed with an increase in AOD from as low as 0.06 (equivalent to 100 CCN/cm3) to 0.1 (equivalent to 300 CCN/cm3). Cloud microphysics is different than what is expected in polluted regions. Cloud droplet growth is fast, leading to quicker, but weak rain. The results suggest that the clouds forming in aerosol limited (i.e. pristine) environment are more sensitive to change in AOD (proxy for CCN). The study hypothesized that invigoration of warm clouds to freezing level is favourable over the pristine oceans.
Reference: Koren, I., G. Dagan and O. Altaratz (2014): From aerosol-limited to invigoration of warm convective clouds, Science, 344: 1143-1146.
3. A new size-composition resolved aerosol model (SCRAM)
A new size-composition resolved aerosol model (SCRAM) was presented in this study. The model is capable of simulating the dynamics of externally mixed aerosols. The new model categorizes aerosols by size-resolved composition and simulates dynamic evolution of aerosols due to coagulation, condensation/evaporation, and nucleation. The composition is represented either by mass fraction of individual species or group of species (e.g. inorganic, hydrophobic etc.). Composition and size of the particles are defined by the user. The model offers the possibility to change the mixing state of aerosols. The source code of the model is available at http://cerea.enpc.fr/polyphemus/src/scram-1.0.tar.gz.
It can be modified under the terms of the GNU General Public License.
Reference: Zhu, S., K. N. Sartelet, and C. Seigneur (2015): A size-compsotion resolved aerosol model for simulating the dynamics of externally mixed particles: SCRAM (v 1.0), Geoscientific Model Development, 8: 1595-1612.
