Intense Dust Research Articles

Retrieval of black carbon and specific absorption over Kanpur city, northern India during 2001–2003 using AERONET data

Column-integrated aerosol black carbon (BC) concentration, [BC] has been retrieved over Kanpur (an industrial city in the Gangetic basin, northern India) during 2001–2003 for the first time. [BC] is derived from BC volume fraction and AERONET-retrieved size distribution using Maxwell–Garnett and Bruggeman mixing rules in a mixture of water, BC and (NH 4) 2SO 4. In addition partly absorbing components like organic carbon (OC) and dust are added to the Maxwell–Garnett mixture depending on the season to investigate their role in the retrieval of [BC]. The volume fraction of each component is retrieved by matching the mixture refractive index (real, n( λ) and imaginary, k( λ)) with AERONET-retrieved refractive index. [BC] shows seasonal variations with high values ( > 10 mg m - 2 ) observed during the post-monsoon and winter seasons and low values ( < 6 mg m - 2 ) during the monsoon season. Specific absorption cross-section ( α a) decreases non-linearly with the increase in [BC], however, the decrease becomes linear when other absorbing components are present. Yearly averaged [BC] and α a are 9.99±1.95, 5.52±1.07, 7.9±1.53 mg m −2 and 7.9±1.83 and 9.67±3.45, 12.74±2.92 m 2 g −1 for 2001, 2002 and 2003, respectively, using Maxwell–Garnett mixing, which differ by ∼15% from those using Bruggeman mixing. [BC] shows diurnal variation with morning and afternoon peaks and mid-day minimum. The amplitude is subdued as it represents the total column, which is more influenced by anthropogenic activities than by boundary layer dynamics. In order to estimate [BC] accurately, OC has to be considered when the absolute difference between k(0.44 μm) and k(1.02 μm) becomes higher than 0.0015. The sensitivity of [BC] due to dust n( λ) becomes important during the intense dust loading period. It was found that [BC] is more sensitive to dust k( λ) than dust n( λ), as [BC] increases ∼10–13% for 10% rise in k( λ). Retrieved [BC] shows good agreement with the in situ measurements. Therefore our retrieval can be used as an alternate method to infer BC and OC specific absorption globally.

Ground observations of a strong dust storm in Beijing in March 2002

On 20 March 2002, one of the most intense dust storms of the last decade struck Beijing: the total suspended particle (TSP) mass concentrations during the event reached 12 mg/m3 and the visibility was reduced to less than 200 m. Variations in meteorological conditions in the boundary layer were monitored during the event, and changes in the physical properties and chemical composition of the aerosol also were studied. The dust storm was accompanied by a sharp and distinct increase in wind speed, a decrease in relative humidity, and increased mixing in the boundary layer due to turbulence. Back trajectory analysis and meteorological analysis showed that the main sources of dust particles that affected Beijing were most likely in southern Mongolia and the western part of Inner Mongolia, China. The amounts of Mg, Al, K, Ca, Ti, V, Cr, Mn, and Fe relative to one another were similar for the dust storm and nondust storm samples, and these elements occurred in near‐crustal proportions. In contrast, both the concentrations and enrichments relative to the crustal reference material for other elements, such as Se, Ni, Pb, Br, and Cu, were much higher during the dust storm than before or afterward. These elements, which are often associated with pollution emissions, apparently originated from distant sources upstream as well as from local sources in Beijing. Even though their enrichments were lower during the dust event, the concentrations of S, Zn, and Cl during the dust storm were higher than in the nondust periods; these results are further evidence that dusty air often contains higher levels of pollutants than nondusty air.

Ground‐based assessment of Total Ozone Mapping Spectrometer (TOMS) data for dust transport over the northeastern Mediterranean

Multiyear daily surface aerosol aluminum (Al) concentration and sunphotometer measurements at Erdemli (Turkey) sampling station were used to assess the performance of Absorbing Aerosol Index (AAI) and Aerosol Optical Thickness (AOT) retrieved from the daily Total Ozone Mapping Spectrometer (TOMS) over the northeastern Mediterranean. A total of 98 moderate‐to‐high intensity dust events with durations from 1 day to 1 week were identified by aerosol Al concentrations and/or TOMS‐AAI above their threshold values of 1.0 μg m−3 and 0.5, respectively. Only 15 events were found to bring appreciable dust load into the northeastern Mediterranean, predominantly below the 850‐hPa pressure level, and therefore were not detected effectively by TOMS. Eight of these events corresponded to short‐range high intensity intrusions (Al &gt; 3.0 μg m−3) from nearby dust sources of the Middle East and Arabian deserts, the rest (seven events) represented moderate‐to‐high intensity (Al &gt; 1.0 μg m−3) long‐range transport from North Africa. Given the highly complex dynamics of the region, the use of TOMS‐AAI data is justified for monitoring Saharan dust transport characteristics in the northeastern Mediterranean. Moreover, the TOMS‐AOT data were found to covary linearly with its counterpart obtained by the ground‐based measurements (correlation coefficient 0.86, significant at &lt;0.001), which lies within the range of estimates suggested by earlier studies.

Estimation of Dry Deposition during Asian Dust Events in Spring of 2002

Dry deposition of Asian dust has been estimated during the intensive dust events in spring 2002 (Period I: 15-24 March 2002, Period II: 4-13 April 2002) using the Asian dust aerosol model (ADAM). The emission module including log-normal distributions of particle size of different soil types of Gobi, Sand, Loess, and Mixed soil in the Asian dust source regions, has been used to calculate the amount of dry deposition. The dry deposition estimated by ADAM is compared with that calculated by using the optical particle counter (OPC) observed at Anmyeondo in Korea. The correlation between the modeled and the calculated dry deposition, is found to be 0.78 and 0.54 in Periods I and II, respectively. The dry deposition velocity depends on the particle size with a minimum value of 0.0272 cm s - 1 and 0.0269 cm s - 1 in the size range of 0.82-1.35 μm in diameter in Periods I and II, respectively. The averaged spectral distribution of dry deposition indicates that the larger particles are more contributed to the total dry deposition amount than the smaller particles due to the large deposition velocity of larger particles. Consequently, the dry deposition rate is found to be higher in regions closer to the Asian dust source regions. The estimated total dry deposition amounts over the South Korea, North Korea and Japan are found to be about 558, 955, and 729 k ton, in Period I, respectively and about 240, 364, and 196 k ton, in Period II, respectively.

Characterization of Atmospheric Mineral Components of PM 2.5 in Beijing and Shanghai, China

Weekly PM 2.5 samples were collected for one year in Beijing and Shanghai and the crustal elements analyzed to investigate the concentration levels and temporal variations of ambient fine mineral dust. The mass concentrations of Al, Si, Ca, Mg, and Fe exhibited similar significant weekly variations in both Beijing and Shanghai. The annual average PM 2.5 concentrations of major crustal elements ranged from 0.27 μg m −3 Mg to 2.48 μg m −3 Si in Beijing, which were 1.40–2.24 times higher than those in Shanghai. Their PM-weighted values were comparable between the two cities. A distinct seasonal pattern was present for these crustal elements with the highest concentrations during the spring in Beijing and during the winter in Shanghai, and the lowest concentrations during the summer in both cities. During the dusty spring of 2000 in Beijing, soil dust was the second most abundant PM 2.5 constituent with a contribution as high as 18.6%, over twice that in the winter. The highest fine soil concentration (37.8 μg m −3) and mass percentage (41.6%) occurred in the same week of intensive dust events impacting Beijing. The impact of dust storms complicates the goal of reducing PM 2.5 in Beijing. Ca originating from construction activities appears to be a significant PM 2.5 contributor as well.

Towards understanding the $\mathsf{\beta}$ Pictoris dust stream

The recent radar detection by [CITE] of a collimated stream of interstellar meteoroids postulated to be sourced at β Pictoris, a nearby star with a prominent dust disk, presents a challenge to theoreticians. Two mechanisms of possible dust ejection from β Pic have been proposed: ejection of dust by radiation pressure from comets in eccentric orbits and by gravity of a hypothetical planet in the disk. Here we re-examine observational data and reconsider theoretical scenarios, substantiating them with detailed modeling to test whether they can explain quantitatively and simultaneously the masses, speeds, and fluxes. Our analysis of the stream geometry and kinematics confirms that β Pic is the most likely source of the stream and suggests that an intensive dust ejection phase took place ~0.7 Myr ago. Our dynamical simulations show that high ejection speeds retrieved from the observations can be explained by both planetary ejection and radiation pressure mechanisms, providing, however, several important constraints. In the planetary ejection scenario, only a “hot Jupiter”-type planet with a semimajor axis of less than 1 AU can be responsible for the stream, and only if the disk was dynamically “heated” by a more distant massive planet. The radiation pressure scenario also requires the presence of a relatively massive planet at several AU or more, that had heated the cometesimal disk before the ejection occurred. Finally, the dust flux measured at Earth can be brought into reasonable agreement with both scenarios, provided that β Pic's protoplanetary disk recently passed through an intensive short-lasting (~0.1 Myr) clearance stage by nascent giant planets, similar to what took place in the early solar system.

Influence of Long-Range Transport Dust Particles on Local Air Quality: A Case Study on Asian Dust Episodes in Taipei during the Spring of 2002

In the spring of 2002, an intensive field measurement campaign was conducted to investigate the impact of Asian dust transport on local air quality in Taipei, Taiwan. The mass concentration, size distribution and chemical composition of the atmospheric aerosols were measured. Air quality data collected by the Taiwan EPA during this period were also analyzed. It was found that the content of crustal elements in aerosols could drastically increase on the arrival of air masses transported from the desert areas in Northwestern China and Mongolia. Time series analysis of aerosol measurements, air quality data, and meteorological conditions identified six Asian dust transport episodes occurring in the spring of 2002. In order to apportion the ambient aerosol burden between local and long-range sources, nitrogen oxides (NO(subscript x)) was chosen as a local pollution tracer and a simplified algorithm based on the NO(subscript x) and PM10 correlation was proposed. It was estimated that long-range transported aerosols contributed as much as 87% to the PM10 in Taipei on Feb. 11, the most intense dust event in 2002. A weak event that occurred on Mar. 23 contributed 35% to the PM10. Our results indicate that the air quality impact due to Asian transport dust is still important even during weak dust events.

Chemical and optical characterization of aerosols measured in spring 2002 at the ACE‐Asia supersite, Zhenbeitai, China

In April 2002, aerosol characteristics have been recorded at Zhenbeitai (ZBT) near the city of Yulin (38°17′N, 109°43′E, Shaanxi province, China). One year earlier, ZBT had been one of the continental supersites of the ACE‐Asia international experiment. In spring, this site, located on the southwestern fringe of the Mu Us desert, is at the crossing of the pathways followed by dust originating from the main Chinese dust sources. During the experiment a customized aerosol sampler has been used. It had been specially designed to ensure the best possible sampling isokineticity for all instruments and to minimize coarse particle losses. Its cutoff size (D50) has been computed to be 9 μm. For particles smaller than this size (PM9), mass concentrations, number concentrations, size distributions, elemental composition, and scattering properties were measured at ground level. Vertically integrated characteristics such as aerosol optical thickness (AOT), or single scattering albedo (ϖ0), were also determined by the means of a Sun‐tracking photometer. During the measurement period, several dust events, one of them a major dust storm when PM9 mass concentrations became as high as 4650 μg/m3, were observed. At this time the aerosol scattering coefficient reached 2800 Mm−1. These dust events were separated by periods when optical properties were altered, or even dominated, by anthropogenic aerosol of local origin. For these periods, PM9 was significantly less (always below 100 μg/m3) than during dust events, mass concentration in black carbon (BC) was between 0.9 and 6.7 μg/m3, and the aerosol scattering coefficient between 7 and 800 Mm−1. No difference in elemental composition could be detected between the various dust episodes. Measured Fe/Al (0.63 ± 0.04) and Mg/Al (0.32 ± 0.03) ratios are consistent with an aerosol source located in the “northwestern high desert sources.” This result is also supported by the air mass back‐trajectories coming from a west or northwest direction and by the fact that dust layers had generally already acquired a significant vertical extension (∼1500 m) when reaching the measurement site. This transported dust had already incorporated an anthropogenic carbonaceous component upon reaching the measurement site. The size distribution of this transported mixture is relatively constant and is characterized by the presence of a particle population with a number mean diameter between 1 and 2 μm. The mass scattering efficiency of this aerosol is 1.05 ± 0.13 m2/g, relative to PM9, and its Angström exponent is close to 0.19. The single scattering albedo determined by data inversion of Sun photometer measurements is found to increase from 0.89 at 441 nm to 0.95 at 873 nm. These relatively large ϖ0 values indicate that, though mixing of mineral dust and anthropogenic aerosols is the rule rather than the exception at ZBT, the aerosol is still not very absorbent during intense dust events. In consequence, the dust optical characteristics measured at ZBT during dust storms are probably representative of the ones of pure dust emitted from the “northwestern high desert” sources.

Chemical composition of mineral dust aerosol during the Saharan Dust Experiment (SHADE) airborne campaign in the Cape Verde region, September 2000

During the Saharan Dust Experiment (SHADE) in September 2000, we collected filter samples on board the Met Office C‐130 aircraft. The main study area was over the Atlantic Ocean between Sal Island and Senegal. Dust was encountered in the altitude range from 0.5–1 to 4–4.5 km. Sublayers with different particle size distributions and different source areas can be distinguished within the main dust plume. Diminution of O3 in anticorrelation with the dust layer suggests removal of O3 by dust particles. Dust loadings containing up to 54 μg m−3 Al (submicron plus supermicron fraction) were measured during particularly intense dust events. Mixing of dust with anthropogenic aerosols, mainly NH4HSO4, was observed in the fine fraction. It was associated with air masses that had originated over Europe and then traveled over North Africa. The ratio of nitrate to non‐sea‐salt sulfate was around 0.3. This argues against any significant influence of biomass burning emissions, which have much higher nitrate. However, we also encountered aged fossil fuel pollution plumes, likely from North America. The geochemical signature of mineral dust was consistent with previous results in the area. Si, Fe, and Ti were not enriched with respect to the soil composition, while other elements, such as Ca and S, were. Ca is prevalently present as calcite in African soils, but it is also found as calcium sulfate in the atmosphere.

Two Molecular Clouds near M17

We present fully sampled images in the C18O J = 2-1 line extending over 13' × 23', made with the Heinrich Hertz Telescope (HHT) on Mount Graham, AZ. The HHT has a resolution of 35'' at the line frequency. This region includes two molecular clouds. Cloud A, to the north, is more compact, while cloud B is to the west of the H II region M17. Cloud B contains the well-known source M17SW. In C18O we find 13 maxima in cloud A and 39 in cloud B. Sixteen sources in cloud B are in M17SW, mapped previously with higher resolution. In cloud B, sources outside M17SW have line widths comparable to those in M17SW. In comparison, cloud A has lower C18O line intensities and smaller line widths but comparable densities and sizes. Maps of the cores of these clouds were also obtained in the J = 5-4 line of CS, which traces higher H2 densities. Our images of the cores of clouds A and B show that for VLSR ≤ 20 km s-1, the peaks of the CS emission are shifted closer to the H II region than the C18O maxima, so higher densities are found toward the H II region. Our CS data give additional support to the already strong evidence that M17SW and nearby regions are heated and compressed by the H II region. Our data show that cloud A has a smaller interaction with the H II region. We surmise that M17SW was an initially denser region, and the turn-on of the H II region will make this the next region of massive star formation. Outside of M17SW, the only other obvious star formation region may be in cloud A, since there is an intense millimeter dust continuum peak found by Henning et al. (1998) but no corresponding C18O maximum. If the CO/H2 ratio is constant, the dust must have a temperature of ~100 K or the H2 density is greater than 106 cm-3 or both to reconcile the C18O and dust data. Alternatively, if the CO/H2 ratio is low, perhaps much of the CO is depleted.

CHARACTERIZATION OF DUST STORMS TO HONG KONG IN APRIL 1998

In April 1998, two intense dust storms were generated in Central Asia and transported eastward across East Asia (15 and 19 April). This article presents the chemical characterization of Hong Kong (HK) aerosols during the dust storms. During the 15 April dust storm, hourly respiratory suspended particles (RSP) (particle diameter smaller than 10 µm) concentrations monitored at 7 sites in Hong Kong reached the peak values synchronously between 9 and 11 a.m. on 17 April, in which the highest concentration was 267 µ gm −3 . Analysis of the RSP samples showed that concentrations of crustal elements (Ba, Ca, Cd, Cr, Fe, Mg, K + ) and anthropogenic species (As, Ni, Pb, Zn, NH + ,N O − ,S O 2− 4 and total carbon) were substantially enhanced. Enhancement of these species was more than a factor of 2 to 14 relative to the non dust period. The total carbon content was high, at 59 µ gm −3 (not including carbonate), and the enrichment factors of As and Pb on 17 April were 122 and 117, respectively. This implied that anthropogenic materials together with mineral dust were transported to HK from Mainland China. Based on material balance calculations, mineral dust contributed 41% to the observed RSP mass on 17 April, which was 2 times that of the nondust sample (22%). From the 5-day backward trajectory analysis, this storm was transported directly from Northwest China to HK. However, there was no corresponding observation for the 19 April dust storm aerosol. Consequently, 15 April storm had stronger impact on HK's atmosphere than 19 April storm. Compared to the HK Air Quality Objective, 15 April dust storm did not cause serious air pollution in HK.

Estimation of the concentration and chemical composition of kosa aerosols at their origin

Kosa aerosols are formed of mineral dust lifted into the atmosphere by dust storms generated over the Asian continent. An intense dust storm which lifted kosa particles into the atmosphere was generated over the Badain Jaran Desert, China from 14 to 15 April 1998. We sampled the kosa aerosol at seven locations in China and Japan along its transport route, and investigated aerosol mass concentrations and the concentrations of chemical components in the aerosol. The aerosol mass concentrations and concentrations of crustal elements in the aerosols decreased exponentially with the distance from the kosa aerosol source. The chemical composition of the kosa aerosol at source, estimated from regressions of aerosol crustal element concentrations on distance from the kosa source, closely coincided with those of simulated Asian mineral dust certified reference material (CJ-2) prepared from the desert surface soil. The estimated concentration of Al in the kosa source aerosol was 5.3×10 3 μg m −3 and the aerosol mass concentration was 9.0×10 4 μg m −3.

Asian dust events of April 1998

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‐UV 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 μg/m3 with local peaks &gt;100 μg/m3. The dust mass mean diameter was 2–3 μm, 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.

A Model for Long-Range Transport of Desert Dust

An Eulerian model for dust transport in the atmosphere is designed, and a new parameterization scheme for dust uptake is developed. The model results are quantitatively compared with satellite observations for an intense dust transport event that occurred over the western Mediterranean in July 1985, showing a high degree of agreement.

Two‐year simulations of seasonal and interannual changes of the Saharan dust emissions

Using a soil‐derived dust emission scheme, the annual and monthly dust emissions in the western “dry” Sahara have been estimated for 1991 and 1992, respectively to 665 Mt and 586 Mt. Based on these simulations, an investigation of the seasonal and annual changes in dust emissions has been performed. The monthly dust emissions vary from 163 Mt in March 1991 to 8 Mt in December 1992. These seasonal variations are related to changes in the location and area of the source‐regions and in the frequency of dust events. On the opposite, the interannual variations of the dust emissions are due to changes in the occurrence of the most intense dust events.

Constraints from Galileo observations on the origin of jovian dust streams

THE Ulysses spacecraft detected streams of sub-micrometre-sized dust particles as it approached Jupiter in 19921,2. Although interplanetary space was known to contain dust, the presence of discrete streams was completely unexpected. The directions from which the dust grains struck the spacecraft strongly suggested that the source lay somewhere within the Jupiter system. Three origins were proposed, the comet Shoemaker–Levy 9 (ref. 3), Jupiter's gossamer ring4, and the volcanoes on Io5, but there was no definitive evidence for or against any of the options. Here we report the detection by the Galileo spacecraft of even more intense dust streams—including three intense dust storms of month-long duration, with impact rates up to 10 times higher than those observed by Ulysses. Our analysis of the data confirms that the dust streams originate near Jupiter; we are able to rule out a cometary origin, but cannot yet determine conclusively whether the dust comes from Io or the ring.

Dust concentrations and particle-size characteristics of an intense dust haze event: Inland Delta Region, Mali, West Africa

An Intense dust plume was monitored in the Inland Delta region of Mali during the period 27–30 April 1990. The plume was generated by thunder cell downdraughts 500 km from the study site and subsequently carried by low-velocity winds to arrive approximately 28 h after its generation. Peak atmospheric dust concentrations (13,735 ug m- s) measured during the event and under very low wind shear conditions exceeded any previously reported in the literature for dust haze events. Particle-size features of the plume dust indicated a distant source. The distribution of dust-particle sizes was uni-modal with a mean of 3 μm at 10 m. Calculated vertical dust fluxes indicated that, upon arrival of the plume, the vertical flux of particles was not in equilibrium with the local wind shear. This was the result of the very high mass concentrations of dust in the atmosphere. After the peak levels of concentration had passed, the relationship between vertical dust flux and wind shear velocity tended towards a relation which predicts dust moving upwards through the atmosphere, varying with wind shear velocity to the fourth power.

Ejection of dust from Jupiter's gossamer ring

ONE of the most intriguing discoveries of the Ulysses mission so far has been the detection of periodic, collimated streams of high-velocity, submicrometre-sized dust particles emanating from Jupiter1,2. To explain the Ulysses data, Horanyi et al. showed3 that electromagnetic forces within Jupiter's magnetosphere can accelerate and eject small dust particles; they proposed a model in which Io is the source of the dust, and the observed periodicity arises from a resonance between the orbital and rotational periods of Io and Jupiter respectively. Here we argue that the masses and velocities of the detected particles are better explained by an origin in Jupiter's gossamer ring. Following their ejection from the magnetosphere, the dust particles are accelerated by the interplanetary magnetic field (IMF). We find that it is the temporal evolution of the IMF which primarily determines the particle trajectories, and hence which particles reach the spacecraft. Our model explains three main features observed in the Ulysses data: fewer streams are detected before closest approach than after, the observed periodicity is closely related to the solar rotation period, and an extremely intense dust stream is detected immediately after closest approach.

Satellite monitoring of smoke from the Kuwait oil fires

The smoke from the oil fires in Kuwait was easily visible in observations from weather satellites in polar and geosynchronous orbits. A portable work station provided these data for planning the National Center for Atmospheric Research and University of Washington research aircraft flights out of Bahrain during the Kuwait Oil‐Fire Smoke Experiment. Meteosat visible and infrared satellite observations indicate that the smoke often traveled southeast along the west shore of the Persian Gulf as far as Bahrain, at which point it typically turned west or continued south toward the Arabian coast. The smoke was difficult to detect from satellite observations as it moved over water and at large distances from the source during the night from infrared observations. Also notable among the daily satellite images were the frequent, intense dust storms that seemed to form in Syria and northern Iraq and transport dust southeastward over Kuwait, and often to northwestern Saudi Arabia. Clouds were virtually absent during the months of May and June within the first several hundred kilometers along the plume direction. Surface temperatures in Bahrain during April and August 1991 were lower than average by as much as 1°–3.2°C, and are significant compared to the climatological variability of average minimum and mean temperatures for the summer months.

Ulysses dust measurements near Jupiter.

Submicrometer- to micrometer-sized particles were recorded by the Ulysses dust detector within 40 days of the Jupiter flyby. Nine impacts were recorded within 50 Jupiter radii with most of them recorded after closest approach. Three of these impacts are consistent with particles on prograde orbits around Jupiter and the rest are believed to have resulted from gravitationally focused interplanetary dust. From the ratio of the impact rate before the Jupiter flyby to the impact rate after the Jupiter flyby it is concluded that interplanetary dust particles at the distance of Jupiter move on mostly retrograde orbits. On 10 March 1992, Ulysses passed through an intense dust stream. The dust detector recorded 126 impacts within 26 hours. The stream particles were moving on highly inclined and apparently hyperbolic orbits with perihelion distances of >5 astronomical units. Interplanetary dust is lost rather quickly from the solar system through collisions and other mechanisms and must be almost continuously replenished to maintain observed abundances. Dust flux measurements, therefore, give evidence of the recent rates of production from sources such as comets, asteroids, and moons, as well as the possible presence of interstellar grains.