An aerosol climatology of Samoa

An atmospheric monitoring station is operated at Cape Matatula, American Samoa, by the Geophysical Monitoring for Climatic Change program under the National Oceanic and Atmospheric Administration. A nearly continuous record of condensation nucleus (CN) concentration and multiwavelength aerosol scattering extinction coefficient (_sp) is available from mid-1977 to the present. This report presents the 1977–1983 data. The long-term mean of CN concentration is 274 cm^-3 the long-term mean of _sp (550 nm) is 1.54×10^-5, and no significant long-term, annual, or diurnal trend is apparent in either data record.     

Meteorology and haze structure during AGASP-II,Part 2: Canadian Arctic flights, 13–16 April 1986

In April 1986, a well-instrumented NOAA WP-3D research aircraft conducted three flights in the Canadian Arctic tied to the Canadian Atmospheric Environment Service baseline station in Alert, Northwest Territories. Two of the flights were coordinated with the National Aeronautical Establishment of Canada Twin Otter and the University of Washington C-131 research aircraft. The haze observed in the Canadian Arctic was well-aged and mixed throughout the troposphere in concentrations well below those observed during the previous weeks in the Alaskan Arctic. Over the ice, beneath the surface temperature inversion, ozone was generally depleted to near zero. Over the coast at Alert, there is evidence that topography and downslope winds reduce the strength of the inversion, thus allowing lower tropospheric gases and aerosols to mix down to the surface. At the top of the troposphere, an aerosol-depleted region was observed. In the lower stratosphere, aerosol concentrations were elevated above those observed in the troposphere.     

Shortwave aerosol optical depth of Arctic haze measured on board the NOAA WP-3D during AGASP-II,April 1986

Measurements of spectral aerosol optical depth in the Alaskan and Canadian Arctic were made from the NOAA Lockheed WP-3D aircraft as part of the second Arctic Gas and Aerosol Sampling Program (AGASP-II) during April 1986. The flight tracks and altitudes flown enabled measurements of the vertical and horizontal distribution of aerosol optical depth in the troposphere as well as direct determination of the stratospheric component. Tropospheric aerosol optical depth ranged from about 0.1 to 0.7. The factor of 7 variability sometimes occurred within 50 km horizontally; comparable variability occurred within less than 1 to 2 km vertically. The Angstrom exponents of the spectral optical depths ranged from 0.5 to 2.0, and some of the variability was apparently related to distinct aerosol regimes.     

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.     

Coastal CCN measurements at Mace Head with enhanced concentrations in strong winds

Surface measurements of cloud condensation nuclei (CCN) number concentration (cm⁻³) are presented for unmodified marine air and for polluted air at Mace Head, for the years 1994 and 1995. The CCN number concentration active at 0.5% supersaturation is found to be approximately log-normal for marine and polluted air at the site. Values of geometric mean, median and arithmetic mean of CCN number concentration (cm⁻³) for marine air are in the range 124–135, 140–150 and 130–157 for the two years of data. Analysis of CCN number concentration for high wind speed, U, up to 20 m s⁻¹ show enhanced CCN production for U in excess of about 10–12 m s⁻¹. Approximately 7% increase in CCN per 1 m s⁻¹ increase in wind speed is found, up to 17 m s⁻¹. A relationship of the form log₁₀CCN=a+bU is obtained for the periods March 1994 and January, February 1995 for marine air yielding values a of 1.70; 1.90 and b of 0.035 for both periods.     

Relationship of heterogeneous nucleation and condensational growth on aerosol nanoparticles

Heterogeneous nucleation and condensation of dibutylphthalate, octadecane, octadecanol, and octadecanoic acid vapors at various pressures on insoluble AgCl and Ag nanoparticles in a turbulent mixing condensation nuclei counter (TMCNC) have been studied theoretically. A method to interpret the particle size distributions measured with a DMA and estimate the parameters for nucleation on single particles is proposed. Based on this semi-empirical method, the Gibbs free energy is calculated and a rate of heterogeneous nucleation on single particles is estimated directly from the experimental “condensation spectra” of inactive and active CN using the DMA data. In some cases, the dependence of the Gibbs nucleation energy on the vapor supersaturation had two maximums and one minimum, instead of one maximum as described by Gibbs' classical thermodynamics of phase transitions. This phenomenon, called “double barrier nucleation” (DBN) is caused by the surface heterogeneity of nano-CN; this is first experimental verification of DBN that had been previously predicted theoretically. Two types of heterogeneity may be present: topographic or energetic. Focusing on energetic heterogeneity, a theoretical model of DBN for spherical geometry is developed. The surface heterogeneity for insoluble nano-sized CN is shown to be critical to explaining the unusual transformation of a monomodal size distribution of inactive CN into a bimodal distribution of activated CN when coagulation is excluded. Future studies will be directed toward more data for further refining the theory and developing a model that simultaneously accounts for both types of surface heterogeneity of nano-CN.     

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.     

Atmospheric observations of liquid water in cloud and of chemical species in aerosols and gases near the ground and in fallen snow at Svalbard, Arctic

Columnar observations of liquid water and of radar echo intensity in cloud were carried out, using a microwave radiometer and a vertically pointing radar respectively, in Ny-Ålesund, Svalbard. Chemical concentrations were also measured in aerosols, gases and snowfalls. Clouds with a large proportion of liquid water moved over the site after snow clouds, with a much lower liquid water content, had been present for about 16 h. The mass concentrations of most chemical species in snowfalls were lower from the first set of clouds than the second. The NO₃⁻ and SO₄²⁻ concentrations in gases and aerosols associated with the first set of clouds were higher than in the second set, but Cl⁻ concentration was less for the first set than the second.     

Cloud condensation nuclei measurements at Mace Head, Ireland, over the period 1994–2002

Analyses of cloud condensation nuclei (CCN) number concentrations (cm^− 3) measured at the Mace Head Atmospheric Research Station, near Carna, County Galway, Ireland, using a DH Associates Model M1 static thermal diffusion cloud chamber over the period from March 1994 to September 2002 are presented in this work. Air masses are defined as being ‘marine’ if they originate from a wind direction of 180–300° and ‘continental’ air masses are defined as originating from a wind direction of 45–135°. Air masses without such filtering were classified as ‘undefined’ air masses. Air masses were found to be dominated by marine sector air, re-affirming Mace Head as a baseline atmospheric research station. CCN levels for specific air masses at Mace Head were found to be comparable with earlier studies both at Mace Head and elsewhere. Monthly averaged clean marine (wind direction of 180–300° and black carbon absorption coefficient < 1.425 Mm^− 1) CCN and marine CCN varied between 15–247 cm^− 3 and 54–670 cm^− 3, respectively. As expected, significant increases in number concentration were found in continentally sourced CCN over that of marine CCN and were found to follow a log-normal distribution significantly tighter than that of clean marine air masses. No significant trend was found for CCN over the 9-year period. While polluted continental air masses showed a slight increase in CCN concentrations over the winter months, most likely due to increased fuel usage and a lower mixed boundary layer, the dominance of marine sector air arriving at Mace Head, which generally consists of background CCN concentrations, reduced seasonal differences for polluted air. Marine air showed a distinct seasonal pattern, with elevated values occurring over the spring and summer seasons. This is thought to be due to enhanced biogenic aerosol production as a result of phytoplankton bloom activity in the North Atlantic.     

Incorporation of aerosol particles between 25 and 850 nm into cloud elements: measurements with a new complementary sampling system

The interpretation of the physico-chemical processes in clouds is facilitated by segregating in situ cloud elements from their carrier gas and small particles (interstitial aerosol). Thus, the present study focuses on the quantitative phase segregation of interstitial air from cloud phase by two complementary samplers with microphysical on-line analysis of the separated phases. An improved counterflow virtual impactor (CVI) was developed for the collection and subsequent evaporation of the condensed phase, releasing dissolved gaseous material and residual particles. This sampler operates in the size range of few micrometers up to 50 μm in cloud element diameter and is matched by an interstitial Round Jet Impactor sampling the gas phase with interstitial particles. Calibrations of both samplers verified the calculated cut sizes D₅₀ of 4, 5, and 6 μm and quantified the slope of the collection efficiency curves. Until this study no direct CVI measurements of the residual particle sizes far below the diameter of 0.1 μm were available. For the first time a CVI was connected to a Differential Mobility Particle Sizer (DMPS) scanning between 25 nm and 850 nm, thus, including the entire Aitken mode in the residual size analysis. Cloud studies on the Puy de Dôme, France, revealed residual particle sizes including Aitken mode (diameter D<100 nm) and accumulation mode (D>100 nm). A major feature of the CVI data is expressed by the fact that despite incomplete incorporation of accumulation mode particles in cloud elements there are contributions of particles with diameters smaller than 0.1 μm to the number of residual particles. Cloud entrainment from height levels above the maximum supersaturation as wells as the size-dependent chemical composition of the aerosol population most likely produced the S-shaped size-dependent partitioning of residual particles. Compared to earlier studies the 50% partitioning diameters dropped significantly below 100 nm to roughly 70 nm.     

Dimethylsulfide oxidation and the ratio of methanesulfonate to non sea-salt sulfate in the marine aerosol

A box model of DMS oxidation in the clean, low-NO _x marine atmospheric boundary layer has been used to predict the latitude dependence of the aerosol methanesulfonate to non sea-salt sulfate ratio. The observed latitude dependence of this ratio in the Southern Hemisphere can be reproduced reasonably well if the full suite of reactions proposed by Yin et al. (1990a) is employed, and a strong temperature dependence is specified in the rates of decomposition of CH₃SO₂ and CH₃SO₃ radicals.     

Active Nitrogen in Surface Ozone Depletion Events at Alert during Spring 1998

Measurements of NO_x,y were made at Alert, Nunavut, Canada (82.5° N, 62.3° W) during surface layer ozone depletion events. In spring 1998, depletion events were rare and occurred under variable actinic flux, ice fog, and snowfall conditions. NO_y changed by less than 10% between normal, partially depleted, and nearly completely depleted ozone air masses. The observation of a diurnal variation in NO_x under continuous sunlight supports a source from the snowpack but with rapid conversion to nitrogen reservoirs that are primarily deposited to the surface or airborne ice crystals. It was unclear whether NO_x was reduced or enhanced in different stages of the ozone depletion chemistry because of variations in solar and ambient conditions. Because ozone was depleted from 15–20 ppbv to less than 1 ppbv in just over a day in one event it is apparent that the surface source of NO_x did not grossly inhibit the removal of ozone. In another case ozone was shown to be destroyed to less than the 0.5 ppbv detection limit of the instrument. However, simple model calculations show that the rate of depletion of ozone and its final steady-state abundance depend sensitively on the strength of the surface source of NO_x due to competition from ozone production involving NO_x and peroxy radicals. The behavior of the NO/NO₂ ratio was qualitatively consistent with enhanced BrO during the period of active ozone destruction. The model is also used to emphasize that the diurnal partitioning of BrO_x during ozone depletion events is sensitive to even sub ppbv variations in O₃.     

黄山地区不同高度云凝结核的观测分析

为研究华东高山地区云凝结核（Cloud Condensation Nuclei,CCN）沿山峰的垂直变化特征,2011年6月利用云凝结核计数器（Cloud Condensation Nuclei Counter,CCNC）在黄山三个不同高度处对CCN进行观测。观测结果表明,不同高度的CCN浓度随时间的变化趋势基本一致,CCN浓度随高度的升高而减小,过饱和度为0.8%时山顶、山腰、山底CCN浓度平均值分别为1105.62、1218.39和1777.78 cm-3,山底的高CCN浓度（大于1000 cm-3）出现频率大于山腰和山顶,表明山底受周边污染源的影响较山顶和山腰大。山顶和山底的日变化曲线均为双峰型,两个峰值分别出现在午前和午后,与大气边界层高度及山谷风变化有关。利用公式N=CSk拟合了山顶在不同天气条件下CCN活化谱,并分析了其变化特征。结果显示,晴天、雨天和雾天的C值分别为2798、384、765,小于一些污染城市,属于清洁大陆型核谱。本文结果有助于改进对华东背景地区云凝结核时空分布的认识,为该地区云雾核化在数值模式中的表达提供观测依据和参数化方案。     

Ceilometer observations of aerosol layer structure above the Petit Lubéron during ESCOMPTE's IOP 2

A modified ceilometer has been used during the second Intensive Observation Period (IOP) of the “Expérience sur Site pour COntraindre les Modèles de Pollution atmosphériques et de Transport d'Émission” (ESCOMPTE) to perform continuous remote observations of aerosol accumulations in the first 3 km of the atmosphere. These observations encompassed an episode of intense particulate and photochemical pollution. The submicronic particles density, measured at an altitude of 600 m, went from a very low point of a few tens of particles per cubic centimeter (at the end of a Mistral episode in the free atmosphere) to a high point of more than 4500 particles per cubic centimeter (when pollutants were trapped by thermal inversions).The main result is that this instrument enables a fine documentation of the mixing layer height and of aerosol particles stratifications and circulation. Airborne aerosol measurements have been made above the mountainous region of Mérindol in order to validate in situ the remote sensing measurements. Ozone measurements near the summit of the mountains as well as in the valley were performed in order to correlate aerosol accumulation and ozone concentration. As a notable example, the two-layer aerosol stratification seen in the first 2 days of IOP 2b in that part of the ESCOMPTE domain confirms the results of another team which used backtrajectories. The low-altitude pollution for this timeframe had a local origin (the Fos industrial area), whereas above 500 m, the air masses had undergone regional-scale transport (from north-eastern Spain).The second major result is the highlighting of a pattern, in sea breeze conditions and in this part of the ESCOMPTE experiment zone, of nocturnal aerosol accumulation at an altitude of between 500 and 2000 m, followed by high ozone concentration the next day.     

北极臭氧损耗对初春东亚中高纬地区地面气温影响的观测分析

利用1948—2007年NCEP/NCAR月平均2m地面气温再分析资料、3月北极涛动（AO）指数和春季臭氧含量资料,采用合成分析方法分析了北极臭氧损耗对初春东亚中高纬地区地面气温的影响。结果表明,臭氧低（高）值年,3月东亚中高纬地区地面气温存在正（负）异常。4月的与3月类似,但气温异常的幅度减小,中心位置也有所变化。对...     

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.     

The Coordinated Influence of Indian Ocean Sea Surface Temperature and Arctic Sea Ice on Anomalous Northeast China Cold Vortex Activities with Different Paths during Late Summer

The Northeast China cold vortex(NCCV) during late summer(from July to August) is identified and classified into three types in terms of its movement path using machine learning. The relationships of the three types of NCCV intensity with atmospheric circulations in late summer, the sea surface temperature(SST), and Arctic sea ice concentration(SIC) in the preceding months, are analyzed. The sensitivity tests by the Community Atmosphere Model version 5.3(CAM5.3) are used to verify the statistical...