Urban/industrial aerosol: Ground‐based Sun/sky radiometer and airborne in situ measurements

Abstract

Abstract. Both airborne in situ and ground-based remote sensing methods are used to measure the properties of urban/industrial aerosols during the Sulfate Clouds and RadiationmAtlantic (SCAR-A) experiment in 1993. Airborne in situ methods directly measure aerosol characteristics such as size distribution and scattering coefficient at a particular altitude and infer the total column optical properties, such as optical thickness. Ground-based remote sensing is sensitive to the aerosol optical properties of the entire column and infers the physical properties from inversion of sky radiance. Comparison of optical thickness measurements are encouraging but inconclusive because of measured profiles which extend no higher than 2 km. By comparing aerosol volume size distributions we find that the two systems are in agreement in the radius size range 0.05-2/•m, after the stratospheric aerosol mode is removed from the remote sensing data. At larger aerosol sizes both systems suffer from greater uncertainty, and the larger aerosols themselves are less spatially uniform because of their short lifetimes. The combination of factors makes the comparison at larger radii impossible. The disadvantages of the in situ systems are that there is a measuring efficiency for each device which is dependent on aerosol size and that airborne in situ measurements are rare events in time and space. Also, in situ instruments dry the aerosol before measurement. Automatic remote sensing procedures measure the total column ambient aerosol unaffected by drying or sampling issues, and these instruments can be installed globally to make observations many times per day. However, the disadvantages to remote sensing are that the inferred physical properties are dependent on the assumptions and numerical limitations of the inversion procedures. The favorable comparison between the two types of measurement systems suggests that these drawbacks are manageable in both cases.

Analysis of linear long-term trend of aerosol optical thickness derived from SeaWiFS using BAER over Europe and South China

“…The third effect generates a random-like error. The uncertainty from the third effect leads to over-or underestimation of the AOT because cloudy days are underrepresented in the database (Remer et al, 1997;Dubovik et al, 2001). Overall, the three superimposed cloud effects can have a complicated influence on the quality of AOT retrievals, as seen in the difference between AERONET and BAER AOT trends (Figs.…”

Trend analysis of aerosol optical thickness and Ångström exponent derived from the global AERONET spectral observations

“…frequent cloud disturbance (Remer et al, 1997;Dubovik et al, 2002a;Yoon et al, 2011) and coarse temporal resolution of the observation. Therefore, it is necessary to investigate aerosol trends based on ground-based observations.…”

Comparison of aerosol optical depth inferred from surface measurements with that determined by Sun photometry for cloud‐free conditions at a continental U.S. site

“…However, such ideal experiments present challenging experimental difficulties [Remer et al, 1997] and are generally quite limited because of the effort and expenses associated with aircraft operations. Although the aerosol scattering coefficient is readily measured by means of an integrating nephelometer, the measured value is generally not equal to the ambient scattering coefficient because the ambient RH is not identical to that in the nephelometer due to heating of the sample airstream within the nephelometer control volume [Bergin et al, 1997].…”