Sea salt production over Bay of Bengal : Effect of salinity

Abstract:

Marine aerosols constitute one of the most important natural aerosol systems globally and play an important role in global climate regulation and the marine biogenic system. One of the major constituents of the marine aerosol system is sea salt. Sea salt aerosols are produced via the bubble-bursting process resulting from whitecap generation (due to high wind speed). The resulting sea salt particles are of sub micrometre sizes and go up to a few micrometres. An increase in sea salt mass is primarily associated with increasing wind speeds. The increase in wind speed not only increases the mass concentration of the small-sized sea salt particles but also that of higher-sized particles. This behaviour is constrained by other factors like temperature and salinity.

In the present work, this variability in the change in mass concentration of sea salt aerosol is studied with respect to the wind speed variation over Bay of Bengal (BoB). This work includes measurements from two field experiments held on 2006 ((ICARB) March-April) and 2012 ((CTCZ) July-August) over BoB. An analysis of the mass concentration with the wind history showed the mass concentration increasing with the increase in wind speed. Here wind history is used instead of instantaneous wind speed, because it is a good indicator of dependence of mass concentrations on wind speed. However, the cruise held in 2012 showed the size of particles constraining to 2.5 µm unlike the cruise in 2006. This difference in the size of the particles formed is majorly due to change in salinity. In 2012, the cruise was during summer monsoon season wherein the high runoff associated with high precipitation lead to reduced salinity. Whereas in 2006, the cruise was in summer season during which high evaporation lead to increase in salinity. This shows that with lower salinity the sea salt particles formed will be of smaller size. This also shows that apart from wind speed, salinity also affects the sea salt production.