GFDL - Geophysical Fluid Dynamics Laboratory

Mixing of dust and NH3 observed globally over anthropogenic dust sources

August 24th, 2012

P. Ginoux, L. Clarisse, C. Clerbaux, P.-F. Coheur, O. Dubovik, N. C. Hsu, M. Van Damme. Journal: Atmospheric Chemistry and Physics. DOI: 10.5194/acp-12-7351-2012

Summary

Dust is one of the most abundant aerosols in the atmosphere, and by scattering and absorbing solar radiation, it affects climate. Anthropogenic dust is largely ignored in most current climate studies. We show how pervasive it is throughout the world, and that it is mostly associated with croplands.

To verify the existence of anthropogenic dust from agriculture, we evaluated dust mass columns derived from the MODIS Deep Blue satellite from April 2009 to March 2010, with AERONET data. We were able to determine the difference between natural and anthropogenic dust based on optical properties.

This study showed that the properties of natural and anthropogenic dust differ significantly, which implies different impacts on climate. On one hand, anthropogenic dust is iron-rich and is more absorbing than natural dust, such as from dry lakes. On the other hand, we show that dust is mixed with non-absorbing aerosols from agriculture. These two opposite effects are shown to be particle-size dependent.

This is the first study to identify a correlation between dust sources (derived from satellite data) and the NH3column burden globally. This is also the first study to explore the relationship between dust sources and croplands and pastures.

UNCERTAINTIES: No inter-annual variability was taken into account because only one year of NH3concentration was retrieved from the satellite instrument.

Annual distribution of dust over croplands (blue), pastures (green), and other sources (red); and ammonia hot spots (NH3) (yellow contours).
Annual distribution of dust over croplands (blue), pastures (green), and other sources (red); and ammonia hot spots (NH3) (yellow contours).