Atmospheric Aerosol Measurements Research Articles

A review of atmospheric aerosol measurements

Recent developments in atmospheric aerosol measurements are reviewed. The topics included complement those covered in the recent review by Chow (JAWMA 45: 320–382, 1995) which focuses on regulatory compliance measurements and filter measurements of particulate composition. This review focuses on measurements of aerosol integral properties (total number concentration, CCN concentration, optical coefficients, etc.), aerosol physical chemical properties (density, refractive index, equilibrium water content, etc.), measurements of aerosol size distributions, and measurements of size-resolved aerosol composition. Such measurements play an essential role in studies of secondary aerosol formation by atmospheric chemical transformations and enable one to quantify the contributions of various species to effects including light scattering/absorption, health effects, dry deposition, etc. Aerosol measurement evolved from an art to a science in the 1970s following the development of instrumentation to generate monodisperse calibration aerosols of known size, composition, and concentration. While such calibration tools permit precise assessments of instrument responses to known laboratory-generated aerosols, unquantifiable uncertainties remain even when carefully calibrated instruments are used for atmospheric measurements. This is because instrument responses typically depend on aerosol properties including composition, shape, density, etc., which, for atmospheric aerosols, may vary from particle-to-particle and are often unknown. More effort needs to be made to quantify measurement accuracies that can be achieved for realistic atmospheric sampling scenarios. The measurement of organic species in atmospheric particles requires substantial development. Atmospheric aerosols typically include hundreds of organic compounds, and only a small fraction (∼10%) of these can be identified by state-of-the-art analytical methodologies. Even the measurement of the total particulate organic carbon mass concentration is beset by difficulties including the unknown extent of evaporative losses during sampling, adsorption of gas-phase organic compounds onto sampling substrates, and the unknown relationship between carbon mass and mass of the particulate organics. The development of improved methodologies for such measurements should be a high priority for the future. Mass spectrometers that measure the composition of individual particles have recently been developed. It is not clear that these instruments will provide quantitative information on species mass concentrations, and more work is needed to routinely interpret the vast quantities of data generated during field sampling. Nevertheless, these instruments substantially expand the range of atmospheric aerosol issues that can be explored experimentally. These instruments represent the most significant advance in aerosol instrumentation in recent years.

Atmospheric aerosol measurements in the North Atlantic Flight Corridor during project POLINAT-2

Atmospheric aerosol measurements in the North Atlantic Flight Corridor during project POLINAT-2

Algorithms for aerosol retrieval based on scattering calculations

This paper focuses on how to determine an accurate aerosol model based on simulations of light scattering. Our algorithms come from an idea that aerosol characteristics can be estimated in terms of the scattering behavior. The correlation coefficients between measurements of atmospheric aerosols and the simulated values for model particles are used to retrieve aerosol characteristics. The space-borne data by Nimbus7-CZCS at a wavelength 0.67 μm and the photopolarimetric measurements of aerosols with a portable photopolarimeter (FPR2000) at wavelengths of 0.559, 0.662, and 0.811 μm are examined in this work. It is shown here that aerosol models are precisely determined by combining use of polarization measurements and radiance data.

Backscattering measurements of atmospheric aerosols at CO_2 laser wavelengths: implications of aerosol spectral structure on differential-absorption lidar retrievals of molecular species

The volume backscattering coefficients of atmospheric aerosol were measured with a tunable CO2 lidar system at various wavelengths in Utah (a desert environment) along a horizontal path a few meters above the ground. In deducing the aerosol backscattering, a deconvolution (to remove the smearing effect of the long CO2 lidar pulse and the lidar limited bandwidth) and a constrained-slope method were employed. The spectral shape beta(lambda) was similar for all the 13 measurements during a 3-day period. A mean aerosol backscattering-wavelength dependence beta(lambda) was computed from the measurements and used to estimate the error Delta(CL) (concentration-path-length product) in differential-absorption lidar measurements for various gases caused by the systematic aerosol differential backscattering and the error that is due to fluctuations in the aerosol backscattering. The water-vapor concentration-path-length product CL and the average concentration C = <CL>/L for a path length L computed from the range-resolved lidar measurements is consistently in good agreement with the water-vapor concentration measured by a meteorological station. However, I was unable to deduce, reliably, the range-resolved water-vapor concentration C(r), which is the derivative of the range-dependent product CL, because of the effect of residual noise caused mainly by errors in the deconvolved lidar measurements.

Changes in aerosol properties with relative humidity in the remote southern hemisphere marine boundary layer

In situ measurements of atmospheric aerosols have been made from an airborne platform over the remote southern hemisphere ocean in November and December 1995 as part of the First Aerosol Characterization Experiment (ACE 1). A subset of these measurements have been evaluated during three of the flights to characterize the aerosol microphysical and optical properties in the cloud‐free, marine boundary. The relationship between the microphysical and optical characteristics in the size range from 0.3 to 20 μm and relative humidity was evaluated. A new technique is introduced by which the scattering coefficient is derived directly from the optical particle counter measurements. The results of this study indicate that changes in particle volume, effective radius, and optical scattering are strongly related to changes in relative humidity (RH). The observations are in very good agreement with laboratory studies of particle volume changes as a function of relative humidity.

Polarimetric properties of aerosol particles

Retrieval algorithms for scattering particles are shown based on photopolarimeric measurements of sky light over the ocean and multiple scattering simulations of the polarization field. Polarized components of the atmospheric constituents have been measured by a photopolarimeter (named PSR1000) with spectral bands set up to correspond to the ADEOS/POLDER. The POLDER is the first sensor on board the satellite to be designed to observe polarization. It is shown that heterogeneous grains are better than homogeneous models to explain polarimetric properties of atmospheric aerosols, and a Maxwell-Garnett mixing rule for small water-soluble (WS) inclusions in an oceanic (OC) matrix is available to interpret the polarization measurements of atmospheric aerosols over the Seto Inland Sea. We also found during our observations that the value of refractive index of the aerosol, i.e., its chemical composition, varies with time and place rather than particle size.

Optical shape fraction measurements of submicrometre laboratory and atmospheric aerosols

Multi-angle azimuthal measurements of light scattering by individual submicrometre particles have been made with the DAWN-A multi-angle light scattering (MALS) instrument. Variability in azimuthal scattering at a polar angle of has been used to determine spherical and nonspherical fractions of laboratory-produced and atmospheric aerosols classified at mobility diameters of 0.2-m (size parameters of 1.3-5.1). Parameters used for shape fractionation were derived empirically by comparing scattering signatures from crystalline sodium chloride cubes and spherical dioctyl sebacate (DOS) droplets and then applied to test aerosols and atmospheric aerosols sampled at low (3-10%) and high (50-80%) values of relative humidity. DOS and NaCl contrast was great enough to permit their distinction with less than 5% uncertainty for 0.4-m, but contrast was observed to decrease as the size parameter approached unity. Crystalline ammonium sulphate test aerosol appeared mildly aspherical, with nonspherical fraction values in the range 15-40%. Nonspherical fractions of atmospheric aerosols measured during the Southeastern Aerosol and Visibility Study (SEAVS), conducted during July and August of 1995, were generally small (<10%), providing confidence in our application of Mie theory for determination of aerosol optical properties. DAWN-A shape data have been compared with aerosol chemistry and hygroscopicity measured during SEAVS, revealing an overall strong correlation of nonspherical fractions to soil dust content and `less hygroscopic' fractions.

Nephelometer optical response model for the interpretation of atmospheric aerosol measurements

A numerical model evaluating the response of a typical integrating nephelometer is described. The model incorporates the actual scattering geometry as well as the effects of a finite light source, detector size, and a nonideal Lambertian diffuser. An angular scattering weighting function is introduced to provide a tractable approach in numerical calculations and easy application. Using established size distribution ensembles associated with a few representative aerosol types, we compare the calculated response of a real nephelometer with that of an ideal, or perfect, nephelometer. The results indicate that, frequently, the nephelometer-produced aerosol-scattering coefficient is of the order of 10-20% too small; but for some naturally occurring aerosols, the difference may be as large as 40-50%. For a multiple-wavelength nephelometer, the response model can be employed to estimate the expected error in the aerosol-scattering coefficients directly from the measurements themselves.

Multispectral polarization measurements of atmospheric aerosols

This work presents the polarization measurements of atmospheric aerosols and how to estimate optical properties of aerosols based on simulations of polarization field. Polarization degrees of aerosols were measured with our new portable polarimeter, whose spectral coverage is [0.443, 0.865] μm. The observations were undertaken at Meteorological Research Institute (Tsukuba) and Kinki University (Osaka) in 1996. We found the sequential change of aerosol characteristics according to the variation of polarization data on temporal scale.

Volatility measurements of atmospheric aerosols in the mid and South Pacific using a volatility-tandem-differential-mobility-analyzer

Volatility measurements of atmospheric aerosols in the mid and South Pacific using a volatility-tandem-differential-mobility-analyzer

Evaluation of a sectional representation of size distributions for calculating aerosol optical properties

A sectional method for representing the atmospheric aerosol size distribution is evaluated for calculating the optical properties used in atmospheric radiative transfer calculations. Many current atmospheric aerosol models and measurement analysis methods are based on a lognormal representation of the aerosol size distribution. The sectional method offers the advantage over the lognormal size distribution that as the aerosol size distribution evolves with time, for example, as in the case of the Mount Pinatubo stratospheric aerosol, regional haze aerosol, or stack plume particles, the optical properties are computed only once for each size section and do not need to be recomputed as the aerosol size distribution changes. Thus the computational costs are considerably reduced. The sectional approach was evaluated by comparing the aerosol optical properties calculated with a continuous distribution to those calculated with a sectional distribution. The sectional approach was shown to be most accurate when the optical properties were integrated assuming a constant surface area distribution within each section. For a sectional size distribution with nine sections between 0.01 and 10 μm in diameter, the results show a maximum error of 6% for the scattering coefficient, 10% for the phase function, and 4% in the sky radiance. The results indicate that the sectional approach offers an excellent compromise between accuracy and computational efficiency.

Feasible groundbased atmospheric and flux measurements by developing countries in support of satellite data

To allow increasing participation of developing countries in global change studies, ground based measurement systems which can be easily comissioned and provide support to satellite observations so as to fit into global mapping need to be chosen carefully. Those relating to atmospheric parameters (greenhouse gas concentrations, emission fluxes, transport properties, etc.) are discussed here. The simplest and of most immediate interest relate to sources and sinks of CH 4 (primarily from rice paddy fields, animals, wetlands) and N 2O (soils, oceans). Measurement techniques and inter-country campaign plans are discussed. There are also important possibilities of using the same technique for measurements of emissions from biomass burning alongwith ozone measurements coupled with survey of biomass burning areas from satellites. Another major area concerns the proposed ITYO programme (International Troposheric Ozone Year), for which, apart from balloon ozone ascents, use of UV-B radiometry at selected wavelengths is considered. The third area discussed concerns measurements of atmospheric aerosols using Multi-wavelength Radiometer (MWR). In addition, in the last few years, a number of advanced groundlevel systems have been installed at low latitudes, which, if made available widely to developing country scientists, and their participation supported financially, could provide a major opportunity for world class research. These include: the MST radar at Tirupati (India) Chung-Li (Taiwan) and Arecibo, Puerto Rico; the Lidars at Thumba and at Natal, Brazil; and the Laser Heterodyning System and mm-wave radiospectrometer at Delhi.

Acid pollutants in air and precipitaion/deposition at the Sudeten Mountains, Poland

The results of several separately performed field studies on air quality in south-western Poland (Black Triangle) are presented In the period 1988–1993 atmospheric aerosol measurement and precipitation/deposition samples were collected at three locations of mountain region (810–1490 m asl). Precipitation was monitored in forest ecosystem using a 24-gauge network was carried out during June–October 1992 and 1993. The occurence of cloud at ground level over hills is difficult to categorize and quantify in mountain terrain and has constituted a basic part of our studies. Precipitation/deposition samples (seven rain and three cloud collectors) in the Karkonosze Mountains were collected over the period 1994–1995 (four field campaigns were conducted) to examine aqueous chemical interactions between constituents in samples. Meteorological data measured at the site included temperature, humidity, wind speed and direction and the amount of precipitation.

Continuous measurements of size distribution atmospheric aerosol, (NH 4) 2SO 4, H 2SO 4, NH 4NO 3, HNO 3 and NO, NO 2, SO 2, O 3 Near Novosibirsk in 1994 – 1995

Continuous measurements of size distribution atmospheric aerosol, (NH 4) 2SO 4, H 2SO 4, NH 4NO 3, HNO 3 and NO, NO 2, SO 2, O 3 Near Novosibirsk in 1994 – 1995

Atmospheric pollutants and their influence on acidification of rain water at an industrial location on the West Coast OF India

The chemical analysis of rain water samples at 11 locations along with measurements of atmospheric aerosols and their size distributions were made to study the influence of pollutants on acidification of rain water during the monsoon season of 1990 at Chembur-Trombay area, a highly industrialized belt in Bombay region located on the west coast of India. The concentrations of acid precursor gases, namely, SO 2 and NO, emanating from industries were low and their influence on acidification was limited to a few kilometer radius of their sources. Whereas, the deposition of ionic components (Na +, K +, Ca 2+, Mg 2+ and CI −) whose sources are natural (sea and soil) were uniformly distributed throughout the region as compared to those released from man-made sources. The high concentration of alkaline components, especially Ca 2+ from natural sources and NH 3 released from a fertilizer plant, were responsible for neutralising H + ion concentration generated from the acidic components (SO 4 2− and N0 3 −). The variation from acidic (1970s) to alkaline (1990s) nature of rainwater in the area maybe due to the change in the use of fuel from coal to natural gas, which contains less sulphur and also, the pollution control measures taken by the industries.

Airborne differential absorption lidar system for measurements of atmospheric water vapor and aerosols

An airborne differential absorption lidar (DIAL) system has been developed at the NASA Langley Research Center for remote measurements of atmospheric water vapor (H(2)O) and aerosols. A solid-state alexandrite laser with a 1-pm linewidth and > 99.85% spectral purity was used as the on-line transmitter. Solid-state avalanche photodiode detector technology has replaced photomultiplier tubes in the receiver system, providing an average increase by a factor of 1.5-2.5 in the signal-to-noise ratio of the H(2)O measurement. By incorporating advanced diagnostic and data-acquisition instrumentation into other subsystems, we achieved additional improvements in system operational reliability and measurement accuracy. Laboratory spectroscopic measurements of H(2)O absorption-line parameters were perfo med to reduce the uncertainties in our knowledge of the absorption cross sections. Line-center H(2)O absorption cross sections were determined, with errors of 3-6%, for more than 120 lines in the 720-nm region. Flight tests of the system were conducted during 1989-1991 on the NASA Wallops Flight Facility Electra aircraft, and extensive intercomparison measurements were performed with dew-point hygrometers and H(2)O radiosondes. The H(2)O distributions measured with the DIAL system differed by ≤ 10% from the profiles determined with the in situ probes in a variety of atmospheric conditions.

Airborne CO_2 coherent lidar for measurements of atmospheric aerosol and cloud backscatter

An airborne CO(2) coherent lidar has been developed and flown on over 30 flights of the NASA DC-8 research aircraft to obtain aerosol and cloud backscatter and extinction data at a wavelength near 9µm. Designed to operate in either zenith- or nadir-directed modes, the lidar can be used to measure vertical profiles of backscatter throughout the vertical extent of the troposphere and the lower stratosphere. Backscatter measurements in absolute units are obtained through a hard-target calibration methodology. The use of coherent detection results in high sensitivity and narrow field of view, the latter property greatly reducing multiple-scattering effects. Aerosol backscatter profile intercomparisons with other airborne and ground-based CO(2) lidars were conducted during instrument checkout flights over the NASA Ames Research Center before extended depolyment over the Pacific Ocean. Selected results from data taken during the flights over the Pacific Ocean are presented, emphasizing intercom arisons with backscatter profile data obtained at 1.06 µm with a NASA Goddard Space Flight Center Nd:YAG lidar on the same flights.

A global warming forum: scientific, economic, and legal overview

Role of Geophysical and Geoengineering Methods to Solve Problems Related to Global Climatic Change: Radiative, Hydrological and Dynamic Interaction in the Air Space System (D. Yang and W. Yang). The Measurements of Atmospheric Aerosols and Condensation Nuclei and the Potential Role of These Particles in Cloud Formation and Transfer of Radiative Energy (J. Podzimek). What do Data Analyses Tell Us about the Variability of Global Temperature? (A.A. Tsonis and J.B. Elsner) Space-Based Geoengineering Options for Dealing with Global Change (L.M. Jenkins). Results of Analyses of a Lunar-Based Power System to Supply Earth with 30,000 GW of Electric Power (D.R. Criswell and R.D. Waldron). Role of Oceanographic and Geochemical Methods to Provide Evidence for Global Climatic Change: Climate and the Marine Record: Scientific Results of the Ocean Drilling Program (P.D. Rabinowitz and J.G. Baldauf). The Climate Continuum: An Overview of Global Warming and Cooling Throughout the History of Planet Earth (A.D. Socci). Anthropogenic Fossil Carbon Sources of Atmospheric Methane (T.R. Barber and W.M. Sackett). Elevated Sea Surface Temperatures Correlate with Caribbean Coral Reef Bleaching (T.J. Goreau, R.L. Hayes, J.W. Clark, D.J. Basta, and C.N. Robertson). Geochemical Methods to Evaluate Methane Concentrations in Soils and Sediments (R.C. Pflaum). Possible Reduction of Atmospheric CO2 by Iron Fertilization in the Antarctic Ocean (T.-H. Peng). Land-Water Interactions and Climate Change (P. Firth). Global Assessment of Greenhouse Gas Production Including Need for Additional Information: Climate History During the Recent Greenhouse Enhancement (P.J. Michaels and R.C. Balling, Jr.). Environmental and Economic Benefits of Natural Gas Use for Pollution Control (P.R. Dey, E.E. Berkau, and K.B. Schnelle). Methane Emissions to the Global Atmosphere from Coal Mining (R.C. Harriss, T. Bensel, and D. Blaha). What to Do About Greenhouse Warming: Look Before You Leap (S.F. Singer, R. Revelle,and C. Starr). Atmospheric Trace Gases: Sources, Sinks, and Role in Global Change (M.A.K. Khalil). Natural Resource Management needed to Provide Long Term Global Energy and Agricultural Uses: Some Considerations in Applying GIS Technology to the Global Warming Problem (L.K. Smith). Global Warming and Agriculture: A Survey of Economic Anlyses and Preliminary Assessments (H. Onal). Greenhouse Gases and Agriculture (R.B. Jackson, IV). Global Warming and the Water Resources of Sahel (Lake Chad) Region (S.A. Isiorho). Satellite Monitoring of Desert Expansion (H.E. Dregne and C.J. Tucker). The Use of Biofuels to Mitigate Global Warming (M.D. Ackerson, E.C. Clausen, and J.L. Gaddy). Prospects of Agriculture in a Carbon Dioxide Enriched Environment (N.C. Bhattacharya). Legal, Policy, and Education Considerations Required to Properly Evaluate Global Warming Proposals: Beyond Vienna and Montreal-A Global Framework Convention on Greenhouse Gases (D.A. Wirth and D.A. Lashof). The Developing Law of the Atmosphere: Toward a 1992 Rio de Janeiro Convention on Global Environmental Change (J. Lancaster). Global Warming: The Energy Policy Challenge (C. Flavin and N. Lenssen). Japan and the Global Environment (A.S. Miller and C. Moore). Regulatory Aspects of Acid Rain (P.R. Dey, E.E. Berkau, and K.B. Schnelle). A Strategy for Global Environmental Education at the University (S.T. Hussain and R.L. Hayes).

14.P.28 Relationships between chemical constituents in atmospheric aerosol and precipitation water samples

The occurence of cloud at ground level over hills is particularly difficult to categorize and quantify in mountainous terrain, and has constituted a basic part of our studies as described below. Precipitation/deposition samples and the daily atmospheric aerosol measurements were collected in Sudety Mountains during 1988-1992 to determine concentration levels of atmospheric species and major cations, an ions, pH in rainwater. Correlations between chemical species and precipitation water samples were coupled with meteorological data at the measurement network. The influence of altitude on rainfall compositions as a consequence of washout of hill cloud by falling rain (seederfeeder scavenging) was investigated at the Karkonosze National Park (part of Sudety Mountains) in summer months (June-October 1992, 1993).

Composition of Br-containing aerosols and gases related to boundary layer ozone destruction in the arctic

During the third Arctic Gas and Aerosol Sampling Program (March 1989), aircraft measurements of atmospheric gases and aerosols were performed in the European Arctic for the purpose of investigating the phenomenon of boundary layer O 3 destruction. Eight high-volume aerosol filter samples were collected in tropospheric air over the pack ice. In these sampling periods, continuous O 3 measurements were made and trace gases were collected in flasks. For all samples, total elemental bromine collected on the filters in excess of the estimated sea salt component (XSFBr) was found to anticorrelate stronly ( r = −0.90) with the mean ozone concentration observed during the sampling period. These findings are similar to earlier observations at Alert and Barrow. Air samples collected during these periods were analysed for Br-containing gases and hydrocarbons. None of these compounds were well correlated with either O 3 or XSFBr concentration over the course of the experiment. This is probably because variable conditions of local meteorology, atmospheric structure and geographic location influenced the degree to which O 3 was depleted, by affecting the size of the reaction reservoir and the source(s) of the reactants. Samples collected in the surface (∼ 50 m deep) isothermal or slightly stable layer (SSL) over pack ice and with light winds from the direction of the central Arctic showed the highest O 3 depletions. When winds were from the direction of open water, significantly higher O 3 and lower XSFBr values were observed. When the SSL was not present, samples collected below the strong inversion showed less O 3 destruction and lower XSFBr concentrations than similar low altitude samples collected within the SSL. This is consistent with the notion of a larger reservoir volume available for reaction. Gas and aerosol chemistry results were compared for two samples collected close spatially and temporally over ice north of Spitsbergen. Our data indicate that (1) CHBr 3 may be the key organobromine species supplying Br atoms and BrO radicals in a heterogeneous photochemical reaction cycle causing the photolytic destruction of O 3 in the springtime Arctic surface layers, and (2) ambient hydrocarbons (especially C 2H 2) are depleted during O 3 destruction, and may be important in the overall reaction mechanism. This catalytic O 3 depletion process was observed to occur to an extent causing near-total O 3 destruction in the SSL over a 1–2 d period. Thus, relatively rapid photochemical reactions between atmospheric Br, hydrocarbons and aerosols are suggested as driving the photolytic O 3 destruction process.