Chemical composition and source signature of spring aerosol in Seoul, Korea Choi JC, Lee M, Chun Y, Kim J, Oh S JGR-ATM 106 (D16): 18067-18074 AUG 27 2001
Characteristic number size distribution of aerosol during Asian dust period in Korea. Chun Y, Kim J, Choi JC, Boo KO, Oh SN, Lee M ATMOSPHERIC ENVIRONMENT 35 (15): 2715-2721 MAY 2001
Synopsis, transport, and physical characteristics of Asian dust in Korea. Chun YS, Boo KO, Kim J, Park SU, Lee M JGR-ATM. 106 (D16): 18461-18469 AUG 27 2001
Historical records in association with Asian dust events were retrieved from ancient Korean literature, which in conjunction with modern observations, indicate that dust events have occurred most frequently in the springtime during the last two centuries. Recent observations through surface network exhibit that Asian dust took place more often in the western part of the Korean peninsula over the last 20 years. In this study, two dust cases, April 1998 and January 1999, were selected to examine detailed conditions most favorable for dust generation, emission, and transport to Korea and to investigate the effect of dust particles on physical and optical properties of aerosols collected in Seoul. Dust transported to the Korean peninsula is closely linked to dust storms generated in upstream regions of the Yellow River or Manzurian plain, which are known as main source regions. Judged from synoptic conditions for both spring and winter dust events, meteorological settings favorable for dust emission are high surface winds and baroclinic instability at 1.5 km level. A strong wind belt, formed at a 5 km level, expedites dust transport, and this is typically much faster in winter. It was confirmed from a backward trajectory analysis that the air carrying mineral dust particles originated from deserts in central Asia and in 1 day passed through the Korean peninsula during wintertime. The effect of mineral dust on aerosol particles is well depicted in the size-separated number concentrations of aerosols observed in Seoul. In both cases, concentrations of coarse particles larger than 0.82 mum were distinctly enhanced while those of fine particle smaller than 0.5 mum were reduced. The measurements of optical depth also indicate that the atmosphere is more turbid with larger particles during dust events.
Asian dust events of April 1998. Husar RB, Tratt DM, Schichtel BA, Falke SR, Li F, Jaffe D, Gasso S, Gill T, Laulainen NS, Lu F, Reheis MC, Chun Y, Westphal D, Holben BN, Gueymard C, McKendry I, Kuring N, Feldman GC, McClain C, Frouin RJ, Merrill J, DuBois D, Vignola F, Murayama T, Nickovic S, Wilson WE, Sassen K, Sugimoto N, Malm WC. JGR-ATM. 106 (D16): 18317-18330 AUG 27 2001
On April 15 and 19, 1998, two intense dust storms were generated over the Gobi desert by springtime low-pressure systems descending from the northwest. The windblown dust was detected and its evolution followed by its yellow color on SeaWiFS satellite images, routine surface-based monitoring, and through serendipitous observations. The April 15 dust cloud was recirculating, and it was removed by a precipitating weather system over east Asia. The April 19 dust cloud crossed the Pacific Ocean in 5 days, subsided to the surface along the mountain ranges between British Columbia and California, and impacted severely the optical and the concentration environments of the region. In east Asia the dust clouds increased the albedo over the cloudless ocean and land by up to 10-20%, but it reduced the near-UNI cloud reflectance, causing a yellow coloration of all surfaces. The yellow colored backscattering by the dust eludes a plausible explanation using simple Mie theory with constant refractive index. Over the West Coast the dust layer has increased the spectrally uniform optical depth to about 0.4, reduced the direct solar radiation by 30-40%, doubled the diffuse radiation, and caused a whitish discoloration of the blue sky. On April 29 the average excess surface-level dust aerosol concentration over the valleys of the West Coast was about 20-50 mug/m(3) with local peaks > 100 mug/m(3). The dust mass mean diameter was 2-3 mum, and the dust chemical fingerprints were evident throughout the West Coast and extended to Minnesota. The April 1998 dust event has impacted the surface aerosol concentration 2-4 times more than any other dust event since 1988. The dust events were observed and interpreted by an ad hoc international web-based virtual community. It would be useful to set up a community-supported web-based infrastructure to monitor the global aerosol pattern for such extreme aerosol events, to alert and to inform the interested communities, and to facilitate collaborative analysis for improved air quality and disaster management.
Long-range transport of Asian dust to the Lower Fraser Valley, British Columbia, Canada. McKendry IG, Hacker JP, Stull R, Sakiyama S, Mignacca D, Reid K JGR-ATM 106 (D16): 18361-18370 AUG 27 2001
For the first time, long-range transport of "Kosa" mineral aerosol from western China to southwestern British Columbia is documented. This late April 1998 event coincided with an episode of photochemical smog and reduced dispersion in the Lower Fraser Valley (LFV). Filter samples in the region show a massive injection of crustal elements (Si, Fe, Al, and Ca) with concentrations of Si approximately double those previously recorded. Ratios of these elements to Fe are shown to be statistically similar to ratios observed in mineral aerosol events in Hawaii and China. On the basis of the difference between observed and expected elemental concentrations and reconstructed soil mass in the episode, it is estimated that Asian dust contributed 38-55% to observed PM10 in the LFV, the remainder being attributed to local sources. Comparison of the April 1998 event with two spring meteorological analogs is consistent with this estimate. Mesoscale model simulations suggest that mineral dust was incorporated into the planetary boundary layer as a result of strong subsidence over the interior of southern British Columbia and Washington State which permitted interception of lower tropospheric elevated aerosol layers by surface-based mixing processes over mountainous terrain. Surface easterly ("outflow") winds then transported this material into the Lower Fraser Valley where it contributed significantly to total particulate loadings and an intense haze. This mechanism is consistent with the observed spatial and temporal distribution of PM10.
Modeled downward transport of a passive tracer over western North America during an Asian dust event in April 1998. Hacker JP, McKendry IG, Stull RB JOURNAL OF APPLIED METEOROLOGY 40 (9): 1617-1628 2001
An intense Gobi Desert dust storm in April 1998 loaded the midtroposphere with dust that was transported across the Pacific to western North America. The Mesoscale Compressible Community (MC2) model was used to investigate mechanisms causing downward transport of the midtropospheric dust and to explain the high concentrations of particulate matter of less than 10-mum diameter measured in the coastal urban areas of Washington and southern British Columbia. The MC2 was initialized with a thin, horizontally homogeneous layer of passive tracer centered at 650 hPa for a simulation from 0000 UTC 26 April to 0000 UTC 30 April 1998. Model results were in qualitative agreement with observed spatial and temporal patterns of particulate matter, indicating that it captured the important meteorological processes responsible for the horizontal and vertical transport over the last few days of the dust event. A second simulation was performed without topography to isolate the effects of topography on downward transport.
Results show that the dust was advected well east of the North American coast in southwesterly midtropospheric flow, with negligible dust concentration reaching the surface initially. Vertically propagating mountain waves formed during this stage, and differences between downward and upward velocities in these waves could account for a rapid descent of dust to terrain height, where the dust was entrained into the turbulent planetary boundary layer. A deepening outflow (easterly) layer near the surface transported the tracer westward and created a zonal-shear layer that further controlled the tracer advection. Later, the shear layer lifted, leading to a downward hydraulic acceleration along the western slopes, as waves generated in the easterly flow amplified below the shear layer that was just above mountain-crest height. Examination of 10 yr of National Centers for Environmental Prediction-National Center for Atmospheric Research reanalyses suggests that such events are rare.
Ground-based network observation of Asian dust events of April 1998 in east Asia. Murayama T, Sugimoto N, Uno I, Kinoshita K, Aoki K, Hagiwara, Liu ZY, Matsui I, Sakai T, Shibata T, Arao K, Sohn BJ, Won JG, Yoon SC, Li T, Zhou J, Hu HL, Abo M, Iokibe K, Koga R, Iwasaka Y. JGR-ATM. 106 (D16): 18345-18359 AUG 27 2001
We coordinated a ground-based network that has been in use since 1997 to observe Asian dust during springtime. Huge Asian dust events that occurred in the middle of April 1998 were captured by this network. In this paper we present the organization of the network; a description of the instruments, including the lidar, sky radiometer, and optical particle counter; and the results of the observation, and offer discussions regarding the transport mechanism of Asian dust in east Asia using an on-line tracer model. We discussed the time series of the surface concentration and the height distribution of the dust. A cutoff cyclone generated during the dust episode was responsible for trapping and sedimentation during the transportation of the Asian dust, particularly in the southern parts of China and Japan. Horizontal dust images derived from NOAA/AVHRR clearly revealed the structure of the vortex. The lidar network observation confirmed the general pattern of dust height distribution in this event; the height of the major dust layer was about 3 km over Japan but was higher (4 to 5 km) in Seoul and Hefei. A thin dust layer in the upper troposphere was also commonly observed in Hefei and Japan. Evidence of the coexistence of dust and cirrus was shown by the polarization lidar. The lidar network observation of Asian dust and satellite remote sensing provide key information for the study of the transport mechanism of Asian dust. Further extension of the lidar network toward the interior of the continent and the Pacific Rim would reveal the greater global mechanism of the transportation.
Nickovic S., A. Papadopoulos, O.Kakaliagu, and G.Kallos, Model for the prediction of desert dust cycle in the atmosphere
Trans-Pacific yellow sand transport observed in April 1998: A numerical simulation. Uno I, Amano H, Emori S, Kinoshita K, Matsui I, Sugimoto N JGR-ATM 106 (D16): 18331-18344 AUG 27 2001
April 1998 Asian dust event: A southern California perspective. Tratt DM, Frouin RJ, Westphal DL JGR-ATM. 106 (D16): 18371-18379 AUG 27 2001
In late April 1998 an extreme Asian dust episode reached the U.S. western seaboard. This event was observed by several in situ and remote sensing atmospheric measurement stations. Dramatic reductions in boundary layer visibility were recorded and the resultant peak backscatter coefficients exceeded prevailing upper tropospheric background conditions by at least 2 orders of magnitude. An analysis of this event is given using lidar vertical backscatter profilometry, concurrent Sun photometer opacity data, and transport modeling. At San Nicolas Island the measured and modeled aerosol optical thickness at 500 nm increased dramatically from 0.15 on April 25 to 0.52 on April 26-27. Volume size distribution on April 27 exhibited a prominent coarse mode at 1-2 mum radius, and single-scattering albedo was observed to increase from 0.90 in the blue to 0.93 in the near infrared. Concurrent lidar observations tracked the evolution of the plume vertical structure, which consisted of up to three well-defined layers distributed throughout the free troposphere.
April 1998 Asian dust event over the Columbia Plateau. Vaughan JK, Claiborn C, Finn D JGR-ATM. 106 (D16): 18381-18402 AUG 27 2001
Surface-based radiometers can be used to assess the atmospheric aerosol burden. During 1998, two multifilter rotating shadow-band radiometers (MFRSRs), operated by Washington State University (WSU) and by the USDA UV-B program, were used to collect data on the Columbia Plateau atmosphere. Analysis of these data by an automated Langley algorithm provided retrievals for total optical thickness, allowing for calculation of aerosol optical thickness (AOT) and the top-of-atmosphere (TOA) instrument signal. Statistical evaluation of the TOA signal permitted recalculation of optical thickness using the Bouguer-Lambert-Beer law and resulted in improved estimates of aerosol optical thickness (AOT). Results for AOT and the associated Angstrom parameters are presented here for an April 1998 dust event for two colocated Columbia Plateau sites. AOT at 500 nm went from background levels (seasonally dominated by regional windblown dust) of similar to0.2 to more than 0.4 during the event maximum on April 27, not returning to normal levels until April 30. Comparison of 500-nm AOT between the two MFRSR showed a root-mean-square (RMS) difference of 0.016. The Angstrom exponent alpha reached a minimum of similar to0.2, and the beta coefficient reached a maximum of similar to0.35, both on April 27, coincident with the AOT maximum. Contemporaneous aerosol sampling in Spokane. Washington. provided (1) elemental data that strongly support our interpretation of this event as an influx of Asian dust without significant sulfur enrichment and (2) event maximum PM10 measurements similar to 80 mug/ml consistent with Pullman event maximum AOT results, assuming a 3-4 kin thick dust layer.
Fusion of SeaWiFS and TOMS satellite data with surface observations and topographic data during extreme aerosol events. Falke SR, Husar RB, Schichtel BA. JOURNAL OF THE AIR & WASTE MANAGEMENT ASSOCIATION . 51 (11): 1579-1585 NOV 2001
Spaceborne sensors allow near-continuous aerosol monitoring throughout the world. This paper illustrates the fusion of Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) and TOMS satellite data with surface observations and topographic data during four extreme aerosol events: (1) the April 1998 Asian dust storm that impacted the west coast of North America, (2) the May 1998 Central American forest fire smoke that impacted eastern North America, (3) the intense fall 1999 northern California fires, and (4) the massive February 2000 Sahara dust storm. During these dust and smoke events, the aerosol was visualized on true color SeaWiFS images as a distinct yellowish dye, the result of the aerosol increasing the reflectance of darker surfaces (ocean and land) and decreasing the reflectance of clouds. TOMS imagery also indicated increased aerosol absorption in the affected areas, while surface monitors measured major reductions in visual range. Fusing these data aids in the determination of the aerosol's spatial, temporal, and optical properties and provides supporting evidence for characterizing what is being visualized as dust or smoke. A 3-dimensional perspective of the events is obtained when incorporating topographic data and provides insight into the vertical properties of the aerosol plumes.
Windblown dust contributes to high PM2.5 concentrations. Claiborn CS, Finn D, Larson TV, Koenig JQ. JOURNAL OF THE AIR & WASTE MANAGEMENT ASSOCIATION. 50 (8): 1440-1445 AUG 2000
The revised National Ambient Air Quality Standards for PM include fine particulate standards based upon mass measurements of PM2.5. It is possible in arid and semi-arid regions to observe significant coarse mode intrusion in the PM2.5, measurement. In this work, continuous PM10 PM2.5 and PM1.0 were measured during several windblown dust events in Spokane, WA. PM2.5 constituted similar to 30% of the PM10 during the dust event days, compared with similar to 48% on the non-dusty days preceding the dust events. Both PM10 and PM2.5 were enhanced during the dust events. However, PM1.0, was not enhanced during dust storms that originated within the state of Washington. During a dust storm that originated in Asia and impacted Spokane, PM1.0 was also enhanced, although the Asian dust reached Washington during a period of stagnation and poor dispersion, so that local sources were also contributing to high particulate levels. The "intermodal" region of PM, defined as particles ranging in aerodynamic size from 1.0 to 2.5 mu m, was found to represent a significant fraction of PM2.5 (similar to 51%) during windblown dust events, compared with 28% during the non-dusty days before the dust events.