The Lulin Atmospheric Background Station (LABS, 23.47°N 120.87°E, 2862 m ASL) in Central Taiwan was constructed in 2006 and is the only high-altitude background station in the western Pacific region ...for studying the influence of continental outflow. In this study, extensive optical properties of aerosols, including the aerosol light scattering coefficient (σs) and light absorption coefficient (σa), were collected from 2013 to 2014. The intensive optical properties, including mass scattering efficiency (αs), mass absorption efficiency (αa), single scattering albedo (ω), scattering Ångstrӧm exponent (Å), and backscattering fraction (b), were determined and investigated, and the distinct seasonal cycle was observed. The value of αs began to increase in January and reached a maximum in April; the mean in spring was 5.89 m2 g−1 with a standard deviation (SD) of 4.54 m2 g−1 and a 4.48 m2 g−1 interquartile range (IQR: 2.95–7.43 m2 g−1). The trend was similar in αa, with a maximum in March and a monthly mean of 0.84 m2 g−1. The peak values of ω (Mean = 0.92, SD = 0.03, IQR: 0.90–0.93) and Å (Mean = 2.22, SD = 0.61, IQR: 2.12–2.47) occurred in autumn. These annual patterns of optical properties were associated with different long-range transport patterns of air pollutants such as biomass burning (BB) aerosol in spring and potential anthropogenic emissions in autumn. The optical measurements performed at LABS during spring in 2013 were compared with those simultaneously performed at the Doi Ang Kang Meteorology Station, Chiang Mai Province, Thailand (DAK, 19.93°N, 99.05°E, 1536 m a.s.l.), which is located in the Southeast Asia BB source region. Furthermore, the relationships among αs, αa, and b were used to characterize the potential aerosol types transported to LABS during different seasons, and the data were inspected according to the HYSPLIT 5-day backward trajectories, which differentiate between different regions of air mass origin.
•Seasonal patterns of aerosol optical properties at LABS were reported.•BB aerosols in the Southeast Asia source region were studied during spring in 2013.•Effects of long-range transport on aerosol optical properties were investigated.•Origins of aerosols transported to LABS in different seasons were characterized.•Observations at LABS were compared with other high-altitude measurements.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The objectives of 7-SEASBASELInE (Seven SouthEast Asian Studies Biomass-burning Aerosols and Stratocumulus Environment: Lifecycles and Interactions Experiment) campaigns in spring 2013-2015 were to ...synergize measurements from uniquely distributed ground-based networks (e.g., AERONET (AErosol RObotic NETwork)), MPLNET ( NASA Micro-Pulse Lidar Network)) and sophisticated platforms (e.g.,SMARTLabs (Surface-based Mobile Atmospheric Research and Testbed Laboratories), regional contributing instruments), along with satellite observations retrievals and regional atmospheric transport chemical models to establish a critically needed database, and to advance our understanding of biomass-burning aerosols and trace gases in Southeast Asia (SEA). We present a satellite-surface perspective of 7-SEASBASELInE and highlight scientific findings concerning: (1) regional meteorology of moisture fields conducive to the production and maintenance of low-level stratiform clouds over land; (2) atmospheric composition in a biomass-burning environment, particularly tracers-markers to serve as important indicators for assessing the state and evolution of atmospheric constituents; (3) applications of remote sensing to air quality and impact on radiative energetics, examining the effect of diurnal variability of boundary-layer height on aerosol loading; (4) aerosol hygroscopicity and ground-based cloud radar measurements in aerosol-cloud processes by advanced cloud ensemble models; and (5) implications of air quality, in terms of toxicity of nanoparticles and trace gases, to human health. This volume is the third 7-SEAS special issue (after Atmospheric Research, vol. 122, 2013; and Atmospheric Environment, vol. 78, 2013) and includes 27 papers published, with emphasis on air quality and aerosol-cloud effects on the environment. BASELInE observations of stratiform clouds over SEA are unique, such clouds are embedded in a heavy aerosol-laden environment and feature characteristically greater stability over land than over ocean, with minimal radar surface clutter at a high vertical spatial resolution. To facilitate an improved understanding of regional aerosol-cloud effects, we envision that future BASELInE-like measurement modeling needs fall into two categories: (1) efficient yet critical in-situ profiling of the boundary layer for validating remote-sensing retrievals and for initializing regional transport chemical and cloud ensemble models; and (2) fully utilizing the high observing frequencies of geostationary satellites for resolving the diurnal cycle of the boundary layerheight as it affects the loading of biomass-burning aerosols, air quality and radiative energetics.
The spring 2015 deployment of a suite of instrumentation at Doi Ang Khang (DAK) in northwestern Thailand enabled the characterization of air masses containing smoke aerosols from burning ...predominantly in Myanmar. Aerosol Robotic Network (AERONET) Sun photometer data were used to validate Moderate Resolution Imaging Spectroradiometer (MODIS) Collection 6 "Deep Blue" aerosol optical depth (AOD) retrievals; MODIS Terra and Aqua provided results of similar quality, with correlation coefficients of 0.93-0.94 and similar agreement within expected uncertainties to global-average performance. Scattering and absorption measurements were used to compare surface and total column aerosol single scatter albedo (SSA); while the two were well-correlated, and showed consistent positive relationships with moisture (increasing SSA through the season as surface relative humidity and total columnar water vapor increased), in situ surface-level SSA was nevertheless significantly lower by 0.12-0.17. This could be related to vertical heterogeneity and/or instrumental issues. DAK is at approximately 1,500 meters above sea level in heterogeneous terrain, and the resulting strong diurnal variability in planetary boundary layer depth above the site leads to high temporal variability in both surface and column measurements, and acts as a controlling factor to the ratio between surface particulate matter (PM) levels and column AOD. In contrast, while some hygroscopic effects were observed relating to aerosol particle size and Angstrom exponent, relative humidity variations appear to be less important for this ratio here. As part of the Seven South-East Asian Studies (7-SEAS) project, the Biomass-burning Aerosols & Stratocumulus Environment: Lifecycles and Interactions Experiment (BASELInE) was intended to probe physicochemical processes, interactions, and feedbacks related to biomass burning aerosols and clouds during the spring burning season (February-April) in southeast Asia (SEA).
The 2013 7-SEASBASELInE campaign over northern Southeast Asia (SEA) provided, for the first time ever, comprehensive ground-based W-band radar measurements of the low-level stratocumulus (Sc) systems ...that often exist during the spring over northern Vietnam in the presence of biomass-burning aerosols. Although spatially limited, ground-based remote sensing observations are generally free of the surface contamination and signal attenuation effects that often hinder space-borne measurements of these low-level cloud systems. Such observations permit detailed measurements of structures and lifecycles of these clouds as part of a broader effort to study potential impacts of these coupled aerosol-cloud systems on local and regional weather and air quality. Introductory analyses of the W-band radar data show these Sc systems generally follow a diurnal cycle, with peak occurrences during the nighttime and early morning hours, often accompanied by light precipitation. Preliminary results from idealized simulations of Sc development over land based on the observations reveal the familiar response of increased numbers and smaller sizes of cloud droplets, along with suppressed drizzle formation, as aerosol concentrations increase. Slight reductions in simulated W-band reflectivity values also are seen with increasing aerosol concentrations and result primarily from decreased droplet sizes. As precipitation can play a large role in removing aerosol from the atmosphere, and thereby improving air quality locally, quantifying feedbacks between aerosols and cloud systems over this region are essential, particularly given the negative impacts of biomass burning on human health in SEA. Such an endeavor should involve improved modeling capabilities along with comprehensive measurements of time-dependent aerosol and cloud profiles.
In this paper, we present recent field studies conducted by NASA's SMART-COMMIT (and ACHIEVE, to be operated in 2013) mobile laboratories, jointly with distributed ground-based networks (e.g., ...AERONET, http://aeronet.gsfc.nasa.gov/ and MPLNET, http://mplnet.gsfc.nasa.gov/) and other contributing instruments over northern Southeast Asia. These three mobile laboratories, collectively called SMARTLabs (cf. http://smartlabs.gsfc.nasa.gov/, Surface-based Mobile Atmospheric Research &Testbed Laboratories) comprise a suite of surface remote sensing and in-situ instruments that are pivotal in providing high spectral and temporal measurements, complementing the collocated spatial observations from various Earth Observing System (EOS) satellites. A satellite-surface perspective and scientific findings, drawn from the BASE-ASIA (2006) field deployment as well as a series of ongoing 7-SEAS (2010–13) field activities over northern Southeast Asia are summarized, concerning (i) regional properties of aerosols from satellite and in-situ measurements, (ii) cloud properties from remote sensing and surface observations, (iii) vertical distribution of aerosols and clouds, and (iv) regional aerosol radiative effects and impact assessment. The aerosol burden over Southeast Asia in boreal spring, attributed to biomass burning, exhibits highly consistent spatial and temporal distribution patterns, with major variability arising from changes in the magnitude of the aerosol loading mediated by processes ranging from large-scale climate factors to diurnal meteorological events. Downwind from the source regions, the tightly coupled-aerosol–cloud system provides a unique, natural laboratory for further exploring the micro- and macro-scale relationships of the complex interactions. The climatic significance is presented through large-scale anti-correlations between aerosol and precipitation anomalies, showing spatial and seasonal variability, but their precise cause-and-effect relationships remain an open-ended question. To facilitate an improved understanding of the regional aerosol radiative effects, which continue to be one of the largest uncertainties in climate forcing, a joint international effort is required and anticipated to commence in springtime 2013 in northern Southeast Asia.
► Multi-year, international efforts for studying aerosol and climate impacts across Southeast Asia. ► Aerosol and cloud properties measured from both ground- and satellite-based platforms. ► Investigation of aerosol–cloud interactions and planning for future experiments.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The Lulin Atmospheric Background Station (LABS, 23.47 deg. N 120.87 deg. E, 2862 m ASL) in Central Taiwan was constructed in 2006 and is the only high-altitude background station in the western ...Pacific region for studying the influence of continental outflow. In this study, extensive optical properties of aerosols, including the aerosol light scattering coefficient Sigma(sub s) and light absorption coefficient Sigma(sub a), were collected from 2013 to 2014. The intensive optical properties, including mass scattering efficiency Sigma(sub s), mass absorption efficiency Sigma(sub a) single scattering albedo (Omega), scattering Angstrom exponent (A), and backscattering fraction (b), were determined and investigated, and the distinct seasonal cycle was observed. The value of Alpha(sub a) began to increase in January and reached a maximum in April; the mean in spring was 5.89 m(exp. 2) g(exp. -1) with a standard deviation (SD) of 4.54 m(exp. 2) g(exp. -1) and a 4.48 m(exp. 2) g(exp. -1) interquartile range (IQR: 2.95-7.43 m(exp. 2) g(exp. -1). The trend was similar in Sigma(sub a), with a maximum in March and a monthly mean of 0.84 m(exp. 2) g(exp. -1). The peak values of Omega (Mean = 0.92, SD = 0.03, IQR: 0.90 - 0.93) and A (Mean = 2.22, SD = 0.61, IQR: 2.12 = 2.47) occurred in autumn. These annual patterns of optical properties were associated with different long-range transport patterns of air pollutants such as biomass burning (BB) aerosol in spring and potential anthropogenic emissions in autumn. The optical measurements performed at LABS during spring in 2013 were compared with those simultaneously performed at the Doi Ang Kang Meteorology Station, Chiang Mai Province, Thailand (DAK, 19.93 deg. N, 99.05 deg. E, 1536 m a.s.l.), which is located in the Southeast Asia BB source region. Furthermore, the relationships among Sigma(sub s), Sigma(sub a), and (b) were used to characterize the potential aerosol types transported to LABS during different seasons, and the data were inspected according to the HYSPLIT 5-day backward trajectories, which differentiate between different regions of air mass origin.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Aerosol optical thickness (τaer) is a fundamental parameter for analyzing aerosol loading and associated radiative effects. The τaer can constrain many inversion algorithms using passive/active ...sensor measurements to retrieve other aerosol properties and/or the abundance of trace gases. In the next wave of spectroradiometric observations from geostationary platforms, we envision that a strategically distributed network of robust, well‐calibrated ground‐based spectroradiometers will comprehensively complement spaceborne measurements in spectral and temporal domains. Spectral τaer can be accurately obtained from direct‐Sun measurements based on the Langley calibration method, which allows for the analysis of distinct spectral features of the calibration results. In this study, we present a spectral τaer retrieval algorithm for an in‐house developed, field deployable spectroradiometer instrument covering wavelengths from ultraviolet to near‐infrared (UV‐Vis‐NIR). The spectral total optical thickness obtained from the Langley calibration method is partitioned into molecular and particulate components by utilizing a least squares method. The resulting high temporal‐resolution τaer and Ångström Exponent can be used effectively for cloud screening. The new algorithm was applied to month‐long measurements acquired from the rooftop at National Aeronautics and Space Administration Goddard Space Flight Center's Building 33. The retrieved τaer demonstrated excellent agreement with those from well‐calibrated Aerosol Robotic Network Sun photometers at all overlapping wavelengths (correlation coefficients higher than 0.98). In addition, empirical stray light corrections considerably improved τaer retrievals at short wavelengths in the UV. The continuous spectrum of τaer from UV‐Vis‐NIR spectroradiometers is expected to provide more informative constraints for retrieval of additional aerosol properties such as refractive indices, size, and bulk vertical distribution.
Key Points
Spectral aerosol optical thickness retrieval algorithm was developed based on the Langley calibration method
Developed empirical stray light correction method considerably improved aerosol optical thickness retrievals at ultraviolet wavelengths
Retrieved spectral aerosol optical thickness provides the key constraints for additional aerosol properties and trace gas retrievals
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Colloidal gels exhibit rheological properties, such as yield stress and viscoelasticity, which arise from the manner in which stress is transmitted through the microstructure. Insight into the ...mechanisms of stress transmission is critical in developing a full understanding of the rheological properties of these materials. Paramount to this is a thorough knowledge of the interparticle interactions. To systematically study the influence of nanoscale particle interactions on gel elasticity and yield stress, we use multiple time-shared optical traps to direct the assembly of colloidal aggregates consisting of dozens of particles. This novel technique provides a direct method of measuring the micromechanical properties and near contact interactions of aggregates that mimic the gel backbone as a function of physicochemical conditions, such as the ionic strength, ionic species, and the presence of surfactant additives. We begin by measuring the response of chain aggregates composed of colloidal PMMA in adhesive contact, due to the presence of inorganic salts in solution, to an applied bending moment. The aggregates were found to exhibit an elastic response below a critical bending moment. The simplified geometry of the aggregate allows us determine the single-bond rigidity from the measured chain elasticity, which is then related to the work of adhesion, WSL, through the Johnson-Kendall-Roberts (JKR) theory of adhesion. Next, we study the effect surfactant additives have on the micromechanics of aggregates. It is observed that both the single-bond elasticity, and the critical bending moment decreases as the surfactant concentration increases. However, ionic surfactants do so more efficiently than non-ionic surfactants. This is a consequence of the greater particle surface charge that arises from the adsorption of ionic surfactants, which in turn results in a larger Columbic repulsion between the particles. Finally, we measure the interactions and micromechanics of colloidal particles confined to an oil-water interface. A very long ranged repulsion is initially observed between particles, in agreement with theoretical descriptions of an electrostatic dipole arising from a small number of dissociated charge groups on the particle surface in the oil phase. As the sample ages, however, the repulsion is found to decrease until the particles are capable of aggregating. The results from this work are expected to aid in the development of improved microrheological models of colloidal gels by providing better descriptions of the near-contact interactions between particles, as well as greater insight into the manner in which stress is transmitted through the gel backbone. These models will permit a greater degree of rational engineering to be incorporated into the development of colloidal gels for industrial applications. (Abstract shortened by UMI.)
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