Capturing vertical profiles of aerosols and black carbon over the Indian Ocean using autonomous unmanned aerial vehicles

摘要

Measurements of the vertical distribution of aerosol properties provideessential information for generating more accurate model estimates ofradiative forcing and atmospheric heating rates compared with employingremotely sensed column averaged properties. A month long campaign over theIndian Ocean during March 2006 investigated the interaction of aerosol,clouds, and radiative effects. Routine vertical profiles of aerosol andwater vapor were determined using autonomous unmanned aerial vehiclesequipped with miniaturized instruments. Comparisons of these airborneinstruments with established ground-based instruments and inaircraft-to-aircraft comparisons demonstrated an agreement within 10%.Aerosol absorption optical depths measured directly using the unmannedaircraft differed from columnar AERONET sun-photometer results by only20%. Measurements of total particle concentration, particle sizedistributions, aerosol absorption and black carbon concentrations arepresented along with the trade wind thermodynamic structure from the surfaceto 3000 m above sea level. Early March revealed a well-mixed layer up to thecloud base at 500 m above mean sea level (m a.s.l.), followed by a decreaseof aerosol concentrations with altitude. The second half of March saw thearrival of a high altitude plume existing above the mixed layer thatoriginated from a continental source and increased aerosol concentrations bymore than tenfold, yet the surface air mass showed little change in aerosolconcentrations and was still predominantly influenced by marine sources.Black carbon concentrations at 1500 m above sea level increased from 70 ng/mto more than 800 ng/m with the arrival of this pollutedplume. The absorption aerosol optical depth increased from as low as 0.005to as much as 0.035 over the same period. The spectral dependence of theaerosol absorption revealed an absorption Angstrom exponent of 1.0, which istypical of an aerosol with most of its absorption attributed to black carbonand generally indicates the absorbing component originated from fossil fuelsources and other high-temperature combustion sources. The results indicatethat surface measurements do not represent the aerosol properties within theelevated layers, especially if these layers are influenced by long rangetransport.