The performance of various empirical linear models to estimate the concentrations of surface-level particulate matter with a diameter less than 10 mu m (PM10) was evaluated using Aerosol Robotic ...Network (AERONET) sun photometer and Moderate-Resolution Imaging Spectroradiometer (MODIS) data collected in Seoul during the Distributed Regional Aerosol Gridded Observation Network (DRAGON)-Asia campaign from March to May 2012. An observed relationship between the PM10 concentration and the aerosol optical depth (AOD) was accounted for by several parameters in the empirical models, including boundary layer height (BLH), relative humidity (RH), and effective radius of the aerosol size distribution (Reff), which was used here for the first time in empirical modeling. Among various empirical models, the model which incorporates both BLH and Reff showed the highest correlation, which indicates the strong influence of BLH and Reff on the PM10 estimations. Meanwhile, the effect of RH on the relationship between AOD and PM10 appeared to be negligible during the campaign period (spring), when RH is generally low in northeast Asia. A large spatial dependency of the empirical model performance was found by categorizing the locations of the collected data into three different site types, which varied in terms of the distances between instruments and source locations. When both AERONET and MODIS data sets were used in the PM10 estimation, the highest correlations between measured and estimated values (R = 0.76 and 0.76 using AERONET and MODIS data, respectively) were found for the residential area (RA) site type, while the poorest correlations (R = 0.61 and 0.68 using AERONET and MODIS data, respectively) were found for the near-source (NS) site type. Significant seasonal variations of empirical model performances for PM10 estimation were found using the data collected at Yonsei University (one of the DRAGON campaign sites) over a period of 17 months including the DRAGON campaign period. The best correlation between measured and estimated PM10 concentrations (R = 0.81) was found in winter, due to the presence of a stagnant air mass and low BLH conditions, which may have resulted in relatively homogeneous aerosol properties within the BLH. On the other hand, the poorest correlation between measured and estimated PM10 concentrations (R = 0.54) was found in spring, due to the influence of the long-range transport of dust to both within and above the BLH.
The AErosol RObotic NETwork (AERONET) estimates of instantaneous solar broadband fluxes (F) at surface have been validated through comparison with ground‐based measurements of broadband fluxes at ...Mauna Loa Observatory (MLO) and by the Baseline Surface Radiation (BSRN) and the Solar Radiation Networks (SolRad‐Net) during the period 1999–2005 and 1999–2006, respectively. The uncertainties in the calculated aerosol radiative forcing (ΔF) and radiative forcing efficiency (ΔFeff) at the bottom of the atmosphere were also assessed. The stations have been selected attempting to cover different aerosols influences and hence radiative properties: urban‐industrial, biomass burning, mineral dust, background continental, maritime aerosols and free troposphere. The AERONET solar downward fluxes at surface agree with ground‐based measurements in all situations, with a correlation higher than 99% whereas the relation of observed to modeled fluxes ranges from 0.98 to 1.02. Globally an overestimation of 9 ± 12 Wm−2 of solar measurements was found, whereas for MLO (clear atmosphere) the differences decrease noticeably up to 2 ± 10 Wm−2. The highest dispersion between AERONET estimates and measurements was observed in locations dominated by mineral dust and mixed aerosols types. In these locations, the F and ΔF uncertainties have shown a modest increase of the differences for high aerosol load, contrary to ΔFeff which are strongly affected by low aerosol load. Overall the discrepancies clustered within 9 ± 12 Wm−2 for ΔF and 28 ± 30 Wm−2 per unit of aerosol optical depth, τ, at 0.55 μm for ΔFeff, where the latter is given for τ(0.44 μm) ≥ 0.4. The error distributions have not shown any significant tendency with other aerosol radiative properties as well as size and shape particles.
Long‐term measurements by the AERONET program of spectral aerosol optical depth, precipitable water, and derived Angstrom exponent were analyzed and compiled into an aerosol optical properties ...climatology. Quality assured monthly means are presented and described for 9 primary sites and 21 additional multiyear sites with distinct aerosol regimes representing tropical biomass burning, boreal forests, midlatitude humid climates, midlatitude dry climates, oceanic sites, desert sites, and background sites. Seasonal trends for each of these nine sites are discussed and climatic averages presented.
Several heavy atmospheric haze pollution episodes occurred over eastern and northern China during January of 2013. The pollution covered more than 100 sq km and caused serious impacts on ...environmental quality, human health, and transportation. In this study, we characterize aerosol microphysical, optical, and radiative characteristics using a combination of ground-based Sun/sky radiometer retrievals and a radiative transfer model. Our results show that during about half of the total number of days, daily PM2.5 and PM10 concentrations are larger than 100 microg/cu m, with maxima of 462 and 433 microg/cu m, respectively, during the haze events. Fine-mode (PM2.5) particles dominated the aerosol size during the episodes. The volume size distribution and median radius of fine-mode particles generally increase as aerosol optical depth at 440 nm (AOD440) increases. The median effective radius of fine-mode particles increases from 0.15 microns at low AOD value (AOD440~0.3) to a radius of 0.25-0.30 microns at high AOD value (AOD440> or = 1.0). The daily mean single-scattering albedo (SSA), imaginary part of refractive index (RI), and asymmetry factor display pronounced spectral behaviors. The overall mean SSA440 and SSA675 are 0.892 and 0.905, respectively. The corresponding RI440 and RI675 are 0.016 and 0.011, respectively. This indicates that a significant amount of absorption occurred under the haze event in Beijing during January 2013. Approximately half of the incident solar radiation energy went into heating the atmosphere as a result of strong aerosol loading and absorption. The daily averaged heating rate in the haze particle layer (0-3.2 km) varies from 0.12 to 0.81 K/day in Beijing, which might exert profound impact on the atmospheric thermodynamic and dynamical structures and cloud development, which should be further studied.
Ground-based observations have insufficient spatial coverage to assess long-term human exposure to fine particulate matter (PM2.5) at the global scale. Satellite remote sensing offers a promising ...approach to provide information on both short- and long-term exposure to PM2.5 at local-to-global scales, but there are limitations and outstanding questions about the accuracy and precision with which ground-level aerosol mass concentrations can be inferred from satellite remote sensing alone. A key source of uncertainty is the global distribution of the relationship between annual average PM2.5 and discontinuous satellite observations of columnar aerosol optical depth (AOD). We have initiated a global network of ground-level monitoring stations designed to evaluate and enhance satellite remote sensing estimates for application in health-effects research and risk assessment. This Surface PARTiculate mAtter Network (SPARTAN) includes a global federation of ground-level monitors of hourly PM2.5 situated primarily in highly populated regions and collocated with existing ground-based sun photometers that measure AOD. The instruments, a three-wavelength nephelometer and impaction filter sampler for both PM2.5 and PM10, are highly autonomous. Hourly PM2.5 concentrations are inferred from the combination of weighed filters and nephelometer data. Data from existing networks were used to develop and evaluate network sampling characteristics. SPARTAN filters are analyzed for mass, black carbon, water-soluble ions, and metals. These measurements provide, in a variety of regions around the world, the key data required to evaluate and enhance satellite-based PM2.5 estimates used for assessing the health effects of aerosols. Mean PM2.5 concentrations across sites vary by more than 1 order of magnitude. Our initial measurements indicate that the ratio of AOD to ground-level PM2.5 is driven temporally and spatially by the vertical profile in aerosol scattering. Spatially this ratio is also strongly influenced by the mass scattering efficiency.
The concept and description of a remote sensing aerosol monitoring network initiated by NASA, developed to support NASA, CNES, and NASDA’s Earth satellite systems under the name AERONET and expanded ...by national and international collaboration, is described. Recent development of weather-resistant automatic sun and sky scanning spectral radiometers enable frequent measurements of atmospheric aerosol optical properties and precipitable water at remote sites. Transmission of automatic measurements via the geostationary satellites GOES and METEOSATS’ Data Collection Systems allows reception and processing in near real-time from approximately 75% of the Earth’s surface and with the expected addition of GMS, the coverage will increase to 90% in 1998. NASA developed a UNIX-based near real-time processing, display and analysis system providing internet access to the emerging global database. Information on the system is available on the project homepage,
http://spamer.gsfc.nasa.gov. The philosophy of an open access database, centralized processing and a user-friendly graphical interface has contributed to the growth of international cooperation for ground-based aerosol monitoring and imposes a standardization for these measurements. The system’s automatic data acquisition, transmission, and processing facilitates aerosol characterization on local, regional, and global scales with applications to transport and radiation budget studies, radiative transfer-modeling and validation of satellite aerosol retrievals. This article discusses the operation and philosophy of the monitoring system, the precision and accuracy of the measuring radiometers, a brief description of the processing system, and access to the database.
Numerous studies indicate the need to account for particle non‐sphericity in modeling the optical properties of dustlike aerosols. The methods for simulating the scattering of light by various ...non‐spherical shapes have rapidly evolved over the last two decades. However, the majority of aerosol remote‐sensing retrievals still rely on the Mie theory because retrievals accounting for particle non‐sphericity are not as well defined methodologically and are demanding computationally. We propose a method for the retrieval of the optical properties of non‐spherical aerosol based on the model of a shape mixture of randomly oriented polydisperse spheroids. This method is applied to angular and spectral radiation measurements from the Aerosol Robotic Network (AERONET) in locations influenced by desert dust. Comparisons with Mie‐based retrievals show a significant improvement in dust‐particle phase functions, size distributions, and refractive indices.
In a joint NRL/Manila Observatory mission, as part of the Seven SouthEast Asian Studies program (7-SEAS), a 2-week, late September 2011 research cruise in the northern Palawan archipelago was ...undertaken to observe the nature of southwest monsoonal aerosol particles in the South China Sea/East Sea (SCS/ES) and Sulu Sea region. Previous analyses suggested this region as a receptor for biomass burning from Borneo and Sumatra for boundary layer air entering the monsoonal trough. Anthropogenic pollution and biofuel emissions are also ubiquitous, as is heavy shipping traffic. Here, we provide an overview of the regional environment during the cruise, a time series of key aerosol and meteorological parameters, and their interrelationships. Overall, this cruise provides a narrative of the processes that control regional aerosol loadings and their possible feedbacks with clouds and precipitation. While 2011 was a moderate El Nino-Southern Oscillation (ENSO) La Nina year, higher burning activity and lower precipitation was more typical of neutral conditions. The large-scale aerosol environment was modulated by the Madden-Julian Oscillation (MJO) and its associated tropical cyclone (TC) activity in a manner consistent with the conceptual analysis performed by Reid et al. (2012). Advancement of the MJO from phase 3 to 6 with accompanying cyclogenesis during the cruise period strengthened flow patterns in the SCS/ES that modulated aerosol life cycle. TC inflow arms of significant convection sometimes span from Sumatra to Luzon, resulting in very low particle concentrations (minimum condensation nuclei CN < 150 cm-3, non-sea-salt PM2.5 < 1 mu g m-3). However, elevated carbon monoxide levels were occasionally observed suggesting passage of polluted air masses whose aerosol particles had been rained out. Conversely, two drier periods occurred with higher aerosol particle concentrations originating from Borneo and Southern Sumatra (CN > 3000 cm-3 and non-sea-salt PM2.5 10-25 mu g m-3). These cases corresponded with two different mechanisms of convection suppression: lower free-tropospheric dry-air intrusion from the Indian Ocean, and large-scale TC-induced subsidence. Veering vertical wind shear also resulted in aerosol transport into this region being mainly in the marine boundary layer (MBL), although lower free troposphere transport was possible on the western sides of Sumatra and Borneo. At the hourly time scale, particle concentrations were observed to be modulated by integer factors through convection and associated cold pools. Geostationary satellite observations suggest that convection often takes the form of squall lines, which are bowed up to 500 km across the monsoonal flow and 50 km wide. These squall lines, initiated by cold pools from large thunderstorms and likely sustained by a veering vertical wind shear and aforementioned mid-troposphere dry layers, propagated over 1500 km across the entirety of the SCS/ES, effectively cutting large swaths of MBL aerosol particles out of the region. Our conclusion is that while large-scale flow patterns are very important in modulating convection, and hence in allowing long-range transport of smoke and pollution, more short-lived phenomena can modulate cloud condensation nuclei (CCN) concentrations in the region, resulting in pockets of clean and polluted MBL air. This will no doubt complicate large scale comparisons of aerosol-cloud interaction.
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