Abstract
Mineral dust aerosols are responsible for some of the largest sources of uncertainties in our current understanding of climate change. Here we show that a severe drought is having a significant impact in one of largest sources of mineral dust aerosols of the U.S., the Owens Lake area in California’s southwest. Measurements of aerosol concentration (PM2.5 particle matter) in the Owens Lake salty playa show that the annual mean concentration of PM2.5 aerosol has been increasing steadily since the beginning of the current drought, with periods of high aerosol concentration increasing from 4 months in 2013 to 9 months in 2015. Interestingly, the PM2.5 aerosol concentration usually increases abruptly from less than ~0.05 mg/m3 to ~0.25 mg/m3. This occurs when saltation events break salt crusts produced by the efflorescence of brine in the salty playa. The brine is produced by either rainfall or runoff water. Based on this observation, we hypothesize that there is an upper limit of ~0.25 mg/m3 in the annual mean PM2.5 aerosols concentration in the Owens Lake basin that might limit the impact of mineral dust aerosols on climate. Indeed, the upper annual limit of ~0.25 mg/m3 has been nearly reached during the current drought.
Highlights
Mineral dust aerosols are responsible for some of the largest sources of uncertainties in our current understanding of climate change
The PM2.5 aerosol concentration usually increases abruptly from less than ~0.05 mg/m3 to ~0.25 mg/m3. This occurs when saltation events break salt crusts produced by the efflorescence of brine in the salty playa
The airborne dust is composed of particles from this anthropogenic source, from the natural desert, and from urban areas of the South Coast of California and the San Joaquin basin[10]
Summary
Mineral dust aerosols are responsible for some of the largest sources of uncertainties in our current understanding of climate change. The PM2.5 aerosol concentration usually increases abruptly from less than ~0.05 mg/m3 to ~0.25 mg/m3 This occurs when saltation events break salt crusts produced by the efflorescence of brine in the salty playa. These events occur when the volumetric soil water content is high (above ~0.8 kg/m3) This observation and the fact that the relative humidity of the near surface air is usually lower during the periods of elevated aerosol concentration indicates that salt crusts inhibit evaporation, contributing to increases in soil water content. Based on the results described above, we hypothesize that the elevated aerosol concentration values observed in 2013, 2014 and 2015 are at least partially the result of nearly continuous breaking of new salt crusts forming on water saturated soil, without the need for precipitation. This is important for the general public and policy makers because the high level of uncertainty in current climate predictions is one the main reasons why their use has lagged in decision making[16]
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