A.D.A. Hansen

The aethalometer — An instrument for the real-time measurement of optical absorption by aerosol particles☆

Abstract We describe an instrument that measures the concentration of optically absorbing aerosol particles in real time. This absorption is normally due to black carbon, which is a good tracer for combustion emission. The minimum resolving times range from seconds in urban environments to minutes in remote locations. We present results obtained during operation on an aircraft. Due to the time resolution capability, we can determine the spatial distributions of absorbing aerosol. From the Greek word “αιϑλoυν,” “to blacken with soot,” we have named this instrument the aethalometer .

Aeolian transport of aerosol black carbon from China to the ocean

Abstract To investigate long-range transport of aerosol black carbon (BC) from China to the downwind seas and ocean, BC concentrations were measured in Beijing city, at a rural station near Beijing city, and at a rural station near Shanghai, for information about source strengths. Aerosol samples were also collected on board research ships in four cruises over the East China Sea and Western Pacific Ocean to determine BC distribution. The data were used to verify a simple one-dimensional transport model. In the marine boundary layer with prevailing westerlies of 5 ms −1 , the BC total deposition rate, including both dry deposition and wet deposition, was computed as −1 × 10 −5 s −1 , and the half-life was estimated to be 19 h. The residence time was approximately 5 d, concentrations subsequently diminishing to the background level. Longer lifetime and farther transport would be probable in the free troposphere. Because BC particles have great surface areas and are very absorbent of electromagnetic waves, their concentration and distribution in the atmosphere may have profound effects on radiation budgets and climate change.

Role of graphitic carbon particles in radiative transfer in the arctic haze

Large concentrations of combustion-generated graphitic carbon particles have been identified at ground level and at altitude in the Arctic atmosphere. Concentrations of these particles during certain times of year and at certain altitudes are comparable to those in urban centers in the United States. These graphitic particles, which have a structure similar to carbon black, have been identified on a molecular level using Raman spectroscopy at sites in the Alaskan, Canadian, and Norwegian Arctic. The black particles are very effective absorbers of solar radiation and can lead to significant heating effects, depending primarily on their distribution in time and space. Recent measurements from an airplane indicate that high concentrations of graphitic particles occur throughout the Arctic troposphere, and at certain altitudes the concentrations can be significantly higher than at ground level. The implications of these results to radiative transfer will be discussed.

Spatial and temporal variations of aerosol sulfate and trace elements in a sourcedominated urban environment

Time-resolved measurements of SO2, sulfate, particulate carbon and trace metal (Pb, As, K, Mn, Fe and V) concentrations were performed simultaneously at four locations in Ljubljana, Yugoslavia, during February and April of 1985. During the winter three different SO42− formation regimes are identified: A—morning period coinciding with maximum emissions and high humidity resulting in maximum SO42− concentrations, with the sulfate formation during this period attributed to fast heterogeneous, aqueous oxidation of local SO2 involving combustion products; B—late evening period with low humidity and high emissions when most SO42− is primary; C—the remainder of the day when SO42− appears to be of a regional origin and formed by a combination of heterogeneous and homogeneous processes. During the non-heating season, the SO42− appears to be of regional origin.

A Concurrent-Flow Cloud Chamber Study of Incorporation of Black Carbon into Droplets

A concurrent-flow cloud chamber (16 cm i.d., 1.5 m high) is described in which cold particle-free and humidified particle-laden air streams were mixed to condense water droplets onto combustion-generated soot particles. Total and interstitial black carbon (BC) concentrations in the cloud were measured as a function of input [BC] and the sample air stream dew point in real time, using a two-channel aethalometer. For black carbon particles produced by the combustion of propane, as much as 90% (by mass) of the black carbon when [BC] 20 μg/m3. It was observed that as sample dew point passed through a maximum, simultaneous maxima were observed in the fraction of black carbon incorporated into droplets and in the amount of black carbon associated with large droplets that settled out of the air stream. The effective supersaturation in the chamber is a function of particle concentration. For black carbon particle concentrations above ∼ 20 μg/m3, the ...

Particulate sulfur and chlorine in Arctic aerosols, spring 1983

Abstract In each of 10 flights of the AGASP Arctic program, particulate sulfur and chlorine were determined by PIXE analysis of eight cascade impactor fractions from 16 μm aerodynamic diameter (μmad). S occurred mainly in fine aerosol sizes of

Estimates of springtime soot and sulfur fluxes entering the Arctic troposphere: Implications to source regions

Abstract A box model calculation is used to make preliminary estimates of the springtime fluxes of carbon and sulfur particles into the Arctic troposphere. These fluxes are large and can only be accounted for by major sulfur and soot sources. Comparison of these fluxes with the amount of fuel burned in various latitude bands indicates that the Arctic haze cannot be due to Arctic sources and strongly suggests that the dominant source regions are below 60°N latitude. Comparisons of Arctic sulfur fluxes with sulfur emissions on a regional and global basis indicate that significant fractions enter the Arctic.

Evidence for heterogeneous SO2 oxidation in Ljubljana, Yugoslavia

Abstract The results of analyses of 24-h wintertime aerosol samples collected during the 1981/82 and 1983/84 sampling periods demonstrate that the highest sulfate formation is observed during periods of high relative humidity and persistent subzero temperatures. Such conditions are conducive to formation of liquid water droplets. The existence of an aqueous mechanism is corroborated by the observed aerosol chloride loss during high sulfate episodes and by the fact that most aerosol sulfate is confined to a particle size range between 0.3 and 2 μm. Soot particles are found in the same size range, indicating the association of aerosol sulfate with combustion products. Under favorable meteorological conditions, up to 20% of the SO 2 may be oxidized to sulfate by heterogeneous mechanisms in winter.

Aerosol studies in Ljubljana under conditions of combustion-derived winter pollution

Ljubljana experiences severe combustion-derived air pollution during winter months. In conjunction with measurements of smoke and SO2, 24-hr winter aerosol samples were analyzed for total particulate carbon and sulfur. The results show that the majority of the particulate carbon is primary soot, that the total sulfur burden (SO2 + particulate sulfur) is combustion derived, and that there appears to be a mechanism for the rapid local conversion of SO2 to sulfate. Since photochemical activity is negligible during these months, a sulfate formation mechanism involving primary combustion products is indicated.

Airborne measurements of aerosol optical properties over south-central new Mexico

Abstract We used a three wavelength nephelometer (449, 536 and 690 nm) and an aethalometer on board the NOAA King Air research aircraft to assess the contributions of aerosol optical scattering and absorption to shortwave extinction. The measurements were made over south-central New Mexico in February and July 1989. The winter measurements revealed a shallow, polluted planetary boundary layer with cleaner air above. The summer measurements showed a uniformly mixed planetary boundary layer extending from ground level to the operational ceiling of 4.5 km above ground. In both cases the total optical thickness values for the column were similar (0.03) and the fractional contribution of aerosol absorption to the extinction was between 5 and 10%. These results suggest that the aerosol extinction in summer and winter is similar, even though the planetary boundary layer thickness is quite different during the two seasons. They also demonstrate that a suitably instrumented light aircraft can profile the optical properties of the troposphere with high sensitivity and good spatial resolution.