Surface aerosol measurements at Barrow during AGASP-II

Measurements at Barrow during the second Arctic Gas and Aerosol Sampling Program (AGASP-II), conducted in April 1986, showed no rapid long-range transport from lower-latitude source regions to Barrow, and only limited vertical transport from above the boundary layer to the surface. New aerosol size distribution measurements in the 0.005–0.1 m diameter size range using a Nuclepore-filter diffusion battery apparatus showed a median diameter of about 0.01 m during times of high condensation nucleus (CN) concentrations. Aerosol black carbon concentrations exceeding 400 ng m^–3 were detected at the surface and were more strongly correlated with CN concentrations than with aerosol scattering extinction (_sp), suggesting that aerosol carbon was generally associated with small particles rather than large particles. Measurements at Barrow during AGASP-I, conducted in March–April 1983, showed a series of aerosol events detected at the ground that were caused by rapid long-range transport paths to the vicinity of Barrow from Eurasia. These events were strongly correlated with aerosol loading in the vertical column (optical depth).     

In-situ measurements of the aerosol size distributions,physicochemistry and light absorption properties of Arctic haze

Thermal and optical techniques were used at Barrow, Alaska during AGASP II (3/20/86–4/7/86) to measure in-situ variability of major aerosol components present in Arctic Haze. The experiment provided continuous data on the concentration, size distribution and relative proportions of sulfate species and refractory aerosol for particle diameters of 0.15 to 5 m. Filter samples were also taken for determination of aerosol optical absorption due to soot (EC-elemental carbon). Although pronounced haze events were absence during this period the haze aerosol present varied in concentration between 2 and 6 g/m³ but showed little change in relative constituents. Apart from local influences, the optical data indicated a persistent fine-mode sulfate aerosol with a NH₄ ⁺/SO₄ ^– molar ratio of about 0.4 and a refractory component of somewhat less than 10% by mass. A preliminary comparison of soot estimates determined from the light absorption data with the size distributions of refractory aerosol observed independently by the optical particle counter showed good agreement during the sample period. In the absence of local pollution, values of single scatter albedo derived from light scattering and light absorption showed similar variation about the average value of 0.86 found by us during flights north of Barrow three years earlier during AGASP I.     

Aerosol black carbon measurements in the Arctic haze during AGASP-II

During the second Arctic Gas and Aerosol Sampling Program conducted in April 1986, we performed measurements of the optically absorbing carbonaceous component of the ambient aerosol from the NOAA WP-3D aircraft operating between sea level and 10 km altitude. We collected the aerosol of filters that were exposed for several hours; we also operated the aethalometer to measure the concentration of aerosol black carbon in real time. The filter analyses represent averages over the altitude range and time span during which the filter was collecting. The real-time results were sorted by altitude to calculate vertical profiles of black carbon concentration. Values typically ranged from 300 to 500 ng m^–3 at lower altitudes, decreasing gradually to 25 to 100 ng m^–3 at 8–10 km. Strong stratification at lower altitudes was frequently observed. The magnitude of these concentrations suggests that the sources are distant regions of considerable fuel consumption. The presence of this material in the tropospheric column and its probable deposition to the high-albedo surface may result in perturbations of the solar radiation balance. The concentrations measured at the highest altitudes may mean that particulate carbon and accompanying emissions for which it is a tracer are mixing into the stratosphere.     

Arctic aerosol and Arctic climate: Results from an energy budget model

An energy budget model is used to study the effect on Arctic climate of optically active aerosol in the Arctic atmosphere. The dependence of the change in surface temperature on the vertical distribution of the aerosol and on the radiative properties of the aerosol-free atmosphere, the Arctic surface, and the aerosol, itself, are calculated. An extensive sensitivity analysis is performed to assess the degree to which the results of the model are dependent upon the assumptions underlying it.List of Symbols Used I ₀ Solar flux at the top of the Arctic Atmosphere (Arctic here means 70° N latitude to the pole) - a _S Surface albedo of the Arctic (a _S ^c is the value of surface albedo at which the sign of the surface temperature perturbation changes) - Reflection coefficient of the aerosol-free Arctic atmosphere - Absorption coefficient of the aerosol-free Arctic atmosphere - Transmission coefficient of the aerosol-free Arctic atmosphere - RI ₀ Total flux of sunlight reflected from the Arctic - A _A I ₀ Total flux of sunlight absorbed in the Arctic atmosphere - A _S I ₀ Total flux of sunlight absorbed at the Arctic surface - A _aer I ₀ Total flux of sunlight absorbed in the Arctic aerosol - Q _A Net atmospheric flow of energy, per unit of Arctic surface area, north across 70° N latitude - Q _S Net oceanic flow of energy, per unit of Arctic surface area, north across 70° N latitude - E Convective plus latent heat fluxes from surface to atmosphere - F _A Net flow of energy to the Arctic atmosphere - F _S Net flow of energy to the Arctic surface - T _A An effective temperature of the Arctic atmosphere - T _S Surface temperature of the Arctic - w Single-scattering albedo of the aerosol - t Optical depth of the aerosol - g Fraction of incident radiation scattered forward by the aerosol - Reflection coefficient of the aerosol - Absorption coefficient of the aerosol - Transmission coefficient of the aerosol - p,q Number of atmospheric layers and the inverse of the fraction of incident IR absorbed in each layer in the energy budget model - F,G,H Measures of the amount of IR-active atmosphere above the surface, the aerosol, and the clouds     

Surface measurements of carbon dioxide and methane at Alert during an Arctic haze event in April, 1986

Carbon dioxide (CO₂) has been measured at Alert by grab flask sampling since 1975 as part of the World Meteorological Organization's Background Air Pollution Monitoring Program. Deviations of CO₂ concentration from the mean annual cycle have previously been attributed to air masses arriving at Alert from the source regions of the industrialized parts of Europe and the Soviet Union. In situ measurements of ambient CO₂ and methane (CH₄) were made at Alert using an automated gas chromatograph, as part of the Arctic Haze Study during April 1986. The temporal behaviour of CO₂ and CH₄ during this period was found to be highly correlated with measurements of particulate sulphate and other atmospheric trace species of anthropogenic origin. Examination of calculated air mass back-trajectories provided further evidence that the observed short-term increases in CO₂ and CH₄ mixing ratios were due to long-range transport from anthropogenic source regions.     

1960年以来东亚季风区云-降水微物理的直接观测研究

云-降水的直接观测结果是云微物理参数化的重要依据。自1960年以来,处于东亚季风影响下的中国实施了大量对云-降水微物理参数的观测和研究,旨在加深对云-降水微物理过程的认识,从而改进数值模式中云微物理参数化方案和指导人工影响天气作业。云-降水微物理参数包括气溶胶、冰核、云滴、雨滴、冰晶、雪晶、冰雹等粒子浓度和谱分布,以及云滴、雨滴含水量等。中国已有云-降水微物理参数的成果可归纳为:(1)通常云-降水微物理粒子浓度变化较大,但总体变化有一定的范围;(2)采用Γ函数拟合云滴谱更接近实际谱,但不同拟合谱参数差异较大;(3)可用指数函数和Γ函数来拟合层状云降水雨滴谱,Γ函数拟合积云和层积混合云降水雨滴谱精度更高;(4)中国冰核浓度较高,冰核浓度随温度的降低近似成指数变化;(5)冰晶谱、雪晶谱、冰雹谱通常采用指数函数来描述;(6)通常使用荣格(Junge)和Γ函数来分段描述气溶胶粒子谱拟合误差更小。由于云-降水过程及其反馈作用描述不准确是数值模式预报结果不确定性的最大因素,中国正在不断地推进云降水的微物理观测研究,以期进一步加深对东亚季风区云-降水微物理特征的认识,从而为模式中微物理参数化方案的改进提供观测依据和科学指导。基于数值预报模式中云微物理过程参数化发展的需要,总结了中国1960年以来云-降水微物理直接观测的研究成果,可为东亚地区云-降水微物理研究及其模式参数化方案的改进提供观测依据。此外,针对云微物理参化发展的需求,结合过去已有的大量观测提出了几点建议,为今后云-降水物理综合性观测方案的设计提供参考。     

What can we learn from aerosol measurements at baseline stations?

In this paper the results of existing baseline aerosol monitoring programs are reviewed. For this purpose, aerosol data from five baseline stations in both hemispheres are analysed. Their information content is compared to that which can be derived when utilizing experiences of recent field experiments and the present state of aerosol sciences in general. Recommendations for extensions and reductions of baseline aerosol measurements are given.     

Elemental composition of particulate material sampled from the Arctic haze aerosol

Thirty-six aerosol filter samples collected in tropospheric Arctic haze layers, in the stratosphere, and in the marine boundary layer during the 1983 Arctic Gas and Aerosol Sampling Program were analyzed for trace elements using instrumental neutron activation analysis. Average crustal dust concentrations were 540 ng/m³ and 330 ng/m³ for samples collected in Arctic haze over the North American and Norwegian Arctic, respectively. An average marine salt concentration of 120 ng/m³ was obtained for haze samples collected above the marine boundary layer on both sides of the Arctic.Meteorological and wind trajectory information were used to identify specific haze transport pathways, which brought relatively unmixed aerosol from the central Soviet Union into the AGASP sampling areas. Results from individual filters collected within these transport zones are discussed, with emphasis on certain trace metal ratos which have been proposed by other researchers as discriminators of aerosols from different source regions. Our aircraft-collected data are compared with previously-collected ground-based measurements, and show reasonably good agreement for most tracer elements and ratios. Specifically, we have determined the As/Sb ratio tracer, named by other researchers as the most effective elemental discriminator of aerosol from the central Soviet Union, to be approximately 5–6. This relatively high tracer value is consistent with previous ground-based findings. A significantly lower V/Sb ratio was observed throughout this study, possibly indicating a change in the source signature.     

The effects of the Arctic haze as determined from airborne radiometric measurements during AGASP II

The interaction of the Aretic winter aerosol (Arctic haze) with solar radiation produces changes in the radiation field that result in the enhancement of scattering and absorption processes which alter the energy balance and solar energy distribution in the Arctic atmosphere-surface system. During the second Arctic Gas and Aerosols Sampling Project (AGASP II) field experiment, we measured radiation parameters using the NOAA WP-3D research aircraft as a platform. State-of-the-art instrumentation was used to measure in situ the absorption of solar radiation by the Arctic atmosphere during severe haze events. Simultaneously with the absorption measurements, we determined optical depths, and total, direct, and scattered radiation fields. All optical measurements were made at spectral bands centered at 412, 500, 675, and 778 nm and with a bandpass of 10 nm. With this selection of spectral regions we concentrated on the measurement of the radiative effects of the aerosol excluding most of the contributions by the gaseous components of the atmosphere. An additional measurement performed during these experiments was the determination of total solar spectrum fluxes. The experimentally determined parameters were used to define an aerosol model that was employed to deduce the absorption by the aerosols over the full solar spectrum and to calculate atmospheric heating rate profiles. The analyses summarized above allowed us to deduce the magnitude of the change in some important parameters. For example, we found changes in instantaneous heating rate of up to about 0.6 K/day. Besides the increased absorption (30 to 40%) and scattering of radiation by the atmosphere, the haze reduces the surface absorption of solar energy by 6 to 10% and the effective planetary albedo over ice surfaces by 3 to 6%. The vertical distribution of the absorbing aerosol is inferred from the flux measurements. Values for the specific absorption of carbon are found to be around 6 m²/g for externally mixed aerosol and about 11.7 m²/g for internally mixed aerosol. A complete study of the radiative effects of the Arctic haze should include infrared measurements and calculations as well as physics of the ice, snow, and water surfaces.     

气溶胶粒子干沉降速度的测量

在昆明和太原地区,通过气溶胶与气象要素的同步观测,得到了粒径范围为0.01—10微米的三个自然模态气溶胶干沉降速度,结果表明:气溶胶粒子的干沉降速度与粒子直径有密切关系.直径大于2微米的粗粒子沉降速度随直径增大而迅速增大;直径小于0.1微米的爱根核模态粒子的沉降速度随直径减小而增大;直径为0.1—2微米的积聚模态的粒子沉降速度出现最小值.这种变化规律虽与国外实验室测定结果在趋势上比较一致,但绝对值却要大得多.另外,沉降速度还与大气稳定度和地面粗糙度有关.     

Studies of ice nucleation by Arctic aerosol on AGASP-II

Aerosol particles were collected on filters for studies of their ability to nucleate ice during the second Arctic Gas and Aerosol Sampling Program (AGASP-II) in April, 1986. The ice nuclei (IN) samples were collected from an aircraft at altitudes ranging from the surface to the vicinity of the tropopause in Arctic locations over Alaska, northern Canada and Greenland. Samples of other components of the aerosol were collected and measurements were made of other properties of the aerosol coincident in time with the IN samples. The IN filters were exposed to water saturation in a dynamic developing chamber at –15° C and –25° C. Ice crystals grew on the IN and were counted on the filters at discrete time intervals during the exposure period to determine the rate of ice nucleation and the final concentration of (IN). Results show that Arctic haze aerosol, identified by pollutant signatures, had lower IN concentrations, a lower IN to total aerosol fraction and slower ice nucleation rates than aerosol which had a chemical signature more indicative of the remote unpolluted troposphere. These observations suggest that the Arctic haze aerosol does not efficiently form ice in the arctic troposphere. This may be a factor contributing to the long-range transport of Arctic haze.