Dust Instrument Research Articles

Ulysses spacecraft in situ detections of cometary dust trails.

The Ulysses spacecraft was launched in 1990 and, after a Jupiter swing-by in 1992, became the first interplanetary spacecraft orbiting the Sun on a highly inclined trajectory with an inclination of [Formula: see text]. The spacecraft was equipped with an impact ionization dust detector which provided 17 years of in situ dust measurements in interplanetary space from 1990 to 2007. Cometary meteoroid streams (also referred to as trails) exist along the orbits of comets, forming fine structures of the interplanetary dust cloud. We use the Interplanetary Meteoroid Environment for eXploration (IMEX) dust streams in space model (Soja RH et al. 2015 Characteristics of the dust trail of 67P/Churyumov-Gerasimenko: an application of the IMEX model. Astron. Astrophys. 583, A18. (doi:10.1051/0004-6361/201526184)) to predict cometary stream traverses by Ulysses and re-analyse the Ulysses dust dataset in order to identify impacts of cometary stream particles detected during such trail traverses. We identify 19 particles compatible with three Ulysses trail traverses on 12 March 1995, 25-27 April 2001 and 16-19 May 2001. The particle origin is compatible with up to five comets, i.e. 10P/Tempel 2, 146P/Shoemaker-LINEAR, 267P/LONEOS and possibly 45P/Honda-Mrkos-Pajdušáková and P/1999 RO28 (LONEOS). We find a dust spatial density in these trails of approximately [Formula: see text]. The radii of the detected cometary stream particles derived from the dust instrument calibration are in the micrometre range. The in situ analysis of meteoroid trail particles in space, which can be traced back to their source bodies, opens a new opportunity for remote compositional analysis of comets and asteroids without the necessity to send a spacecraft to or even land on these celestial bodies, opening new opportunities for future space missions equipped with in situ dust analyzers. This article is part of the theme issue 'Dust in the Solar System and beyond'.

Linking meteorites to their asteroid parent bodies: The capabilities of dust analyzer instruments during asteroid flybys

AbstractLinking meteorites to their asteroid parent bodies remains an outstanding issue. Space‐based dust characterization using impact ionization mass spectrometry is a proven technique for the compositional analysis of individual cosmic dust grains. Here we investigate the feasibility of determining asteroid compositions via cation mass spectrometric analyses of their dust ejecta clouds during low (7–9 km s−1) velocity spacecraft flybys. At these speeds, the dust grain mass spectra are dominated by easily ionized elements and molecular species. Using known bulk mineral volume abundances, we show that it is feasible to discriminate the common meteorite classes of carbonaceous chondrites, ordinary chondrites, and howardite–eucrite–diogenite achondrites, as well as their subtypes, relying solely on the detection of elements with ionization efficiencies of ≤700 or ≤800 kJ mol−1, applicable to low (~7 km s−1) and intermediate (~9 km s−1) flyby speed scenarios, respectively. Including the detection of water ion groups enables greater discrimination between certain meteorite types, and flyby speeds ≥10 km s−1 enhance the diagnostic capabilities of this technique still further. Although additional terrestrial calibration is required, this technique may allow more unequivocal asteroid‐meteorite connections to be determined by spacecraft flybys, emphasizing the utility of dust instruments on future asteroid missions.

The Scientific Need for a Dedicated Interplanetary Dust Instrument at Mars

The Scientific Need for a Dedicated Interplanetary Dust Instrument at Mars

Effect of Relative Humidity on Resuspended Particles Caused by Human Walking

The goal of this study is to investigate the effects of relative humidity on particle resuspension. The experimental study on the resuspension of different size particles is performed in the laboratory at 50%, 60%, 70% and 80% relative humidity separately. The material of flooring is shaggy carpet. The experiments are carried out in a closed room with four laser dust instruments and a laser dust particle counter. The results show that when the relative humidity is 60% and 70%, the resuspension of indoor particulate matter is likely to occur. Human walking has a greater impact on larger-size particles. Under the conditions of different humidity, four situations all follow a rule that the larger the particle size is, the more stable the particle state is.

Flattened loose particles from numerical simulations compared to particles collected by Rosetta

Context.Cometary dust particles are remnants of the primordial accretion of refractory material that occurred during the initial formation stages of the solar system. Understanding their physical structure can help constrain their accretion process.Aims.The in situ study of dust particles that were collected at slow speeds by instruments on board the Rosetta space mission, including GIADA, MIDAS, and COSIMA, can be used to infer the physical properties, size distribution, and typologies of the dust.Methods.We have developed a simple numerical simulation of aggregate impact flattening to interpret the properties of particles collected by COSIMA. The aspect ratios of flattened particles from simulations and observations are compared to distinguish between initial families of aggregates that are characterized by different fractal dimensionsDf. This dimension can differentiate between certain growth modes: the diffusion limited cluster–cluster aggregates (DLCA,Df≈ 1.8), diffusion limited particle–cluster aggregates (DLPA,Df≈ 2.5), reaction limited cluster–cluster aggregates (RLCA,Df≈ 2.1), and reaction limited particle–cluster aggregates (RLPA,Df≈ 3.0).Results.The diversity of aspect ratios measured by COSIMA is consistent with either two families of aggregates with different initialDf(a family of compact aggregates withDfclose to 2.5–3 and some fluffier aggregates withDf≈ 2) or aggregates formed by a single type of aggregation process, such as DLPA. In that case, the cohesive strength of the dust particles must span a wide range to explain the range of aspect ratios observed by COSIMA. Furthermore, variations in cohesive strength and velocity may play a role in the detected higher aspect ratio range (>0.3).Conclusions.Our work allows us to explain the particle morphologies observed by COSIMA and those generated by laboratory experiments in a consistent framework. Taking into account all observations from the three dust instruments on board Rosetta, we favor an interpretation of our simulations based on two different families of dust particles with significantly distinct fractal dimensions that are ejected from the cometary nucleus.

Interstellar dust in the solar system: model versus in situ spacecraft data

Context. In the early 1990s, contemporary interstellar dust penetrating deep into the heliosphere was identified with the in situ dust detector on board the Ulysses spacecraft. Later on, interstellar dust was also identified in the data sets measured with dust instruments on board Galileo, Cassini, and Helios. Ulysses monitored the interstellar dust stream at high ecliptic latitudes for about 16 yr. The three other spacecraft data sets were obtained in the ecliptic plane and cover much shorter time intervals. Aims. To test the reliability of the model predictions, we compare previously published in situ interstellar dust measurements, obtained with these four spacecraft, with predictions of an advanced model for the dynamics of interstellar dust in the inner solar system (Interplanetary Meteoroid environment for EXploration; IMEX). Methods. Micrometer and sub-micrometer-sized dust particles are subject to solar gravity, radiation pressure and the Lorentz force on a charged dust particle moving through the interplanetary magnetic field. These forces lead to a complex size-dependent flow pattern of interstellar dust in the planetary system. The IMEX model was calibrated with the Ulysses interstellar dust measurements and includes these relevant forces. We study the time-resolved flux and mass distribution of interstellar dust in the solar system. Results. The IMEX model agrees with the spacecraft measurements within a factor of 2–3, including time intervals and spatial regions not covered by the original model calibration with the Ulysses data set. The model usually underestimates the dust fluxes measured by the space missions which were not used for the model calibration, i.e. Galileo, Cassini, and Helios. Conclusions. A unique time-dependent model, IMEX is designed to predict the interstellar dust fluxes and mass distributions for the inner and outer solar system. The model is suited to study dust detection conditions for past and future space missions.

Cassini RPWS Dust Observation Near the Janus/Epimetheus Orbit

AbstractDuring the Ring Grazing orbits near the end of Cassini mission, the spacecraft crossed the equatorial plane near the orbit of Janus/Epimetheus (~2.5 Rs). This region is populated with dust particles that can be detected by the Radio and Plasma Wave Science (RPWS) instrument via an electric field antenna signal. Analysis of the voltage waveforms recorded on the RPWS antennas provides estimations of the density and size distribution of the dust particles. Measured RPWS profiles, fitted with Lorentzian functions, are shown to be mostly consistent with the Cosmic Dust Analyzer, the dedicated dust instrument on board Cassini. The thickness of the dusty ring varies between 600 and 1,000 km. The peak location shifts north and south within 100 km of the ring plane, likely a function of the precession phase of Janus orbit.

Cometary Dust.

This review presents our understanding of cometary dust at the end of 2017. For decades, insight about the dust ejected by nuclei of comets had stemmed from remote observations from Earth or Earth's orbit, and from flybys, including the samples of dust returned to Earth for laboratory studies by the Stardust return capsule. The long-duration Rosetta mission has recently provided a huge and unique amount of data, obtained using numerous instruments, including innovative dust instruments, over a wide range of distances from the Sun and from the nucleus. The diverse approaches available to study dust in comets, together with the related theoretical and experimental studies, provide evidence of the composition and physical properties of dust particles, e.g., the presence of a large fraction of carbon in macromolecules, and of aggregates on a wide range of scales. The results have opened vivid discussions on the variety of dust-release processes and on the diversity of dust properties in comets, as well as on the formation of cometary dust, and on its presence in the near-Earth interplanetary medium. These discussions stress the significance of future explorations as a way to decipher the formation and evolution of our Solar System.

Light scattering by hierarchical aggregates

Recent in-situ studies of the environment of comet 67P/Churyumov–Gerasimenko by the dust instruments onboard the Rosetta spacecraft have indicated a complex structure of cometary dust particles. The majority of those particles appeared to be large aggregates of hierarchical structure, i.e. aggregates of particles, which, in turn, were aggregates of smaller particles. This confirmed an earlier hypothesis that dust particles in protoplanetary disks grow under hierarchical growth process. Thus, it is very likely that hierarchical aggregates are common type of natural dust particles. In this paper, we present results of computer simulations of light scattering by a variety of hierarchical aggregates to determine how their structure affects their brightness and polarization phase curves as well as photometric and polarimetric color, and albedo. The computations were done using Multi-Sphere T-Matrix method. Our results show that the type of hierarchical structure of aggregates, specified by the number of particles at each level of hierarchy, causes variations in their light-scattering characteristics, which noticeably exceed the variations caused by different configuration of monomers in the aggregates of the same hierarchical structure. Although we could not find any regularities in the brightness and polarization dependence on the structure of the aggregates, our results clearly show that not only composition or size of aggregates, but also their specific structure should be carefully examined when light scattering by cometary or any other type of dust is modeled. Specifically, we may need to reconsider modeling the cometary dust particles using simple ballistic particle-cluster and cluster-cluster aggregates.

Comet 67P outbursts and quiescent coma at 1.3 au from the Sun: dust properties from Rosetta/VIRTIS-H observations

We present 2-5 $\mu$m spectroscopic observations of the dust coma of 67P/Churyumov-Gerasimenko obtained with the VIRTIS-H instrument onboard Rosetta during two outbursts that occurred on 2015, 13 September 13.6 h UT and 14 September 18.8 h UT at 1.3 AU from the Sun. Scattering and thermal properties measured before the outburst are in the mean of values measured for moderately active comets. The colour temperature excess (or superheat factor) can be attributed to submicrometre-sized particles composed of absorbing material or to porous fractal-like aggregates such as those collected by the Rosetta in situ dust instruments. The power law index of the dust size distribution is in the range 2-3. The sudden increase of infrared emission associated to the outbursts is correlated with a large increase of the colour temperature (from 300 K to up to 630 K) and a change of the dust colour at 2-2.5 $\mu$m from red to blue colours, revealing the presence of very small grains ($\leq$ 100 nm) in the outburst material. In addition, the measured large bolometric albedos ($\sim$ 0.7) indicate bright grains in the ejecta, which could either be silicatic grains, implying the thermal degradation of the carbonaceous material, or icy grains. The 3-$\mu$m absorption band from water ice is not detected in the spectra acquired during the outbursts, whereas signatures of organic compounds near 3.4 $\mu$m are observed in emission. The H$_2$O 2.7-$\mu$m and CO$_2$ 4.3-$\mu$m vibrational bands do not show any enhancement during the outbursts.

Distribution Characteristics of Water Soluble Ions Under Different Weather Conditions During the Youth Olympic Games in Nanjing

To study the variation characteristics of water soluble ions during youth Olympic Games, PM2.5 and water soluble ions were observed by using the beta dust instrument, Anderson 9th sampler and IC type ion chromatography analyzer from August 6 to September 4, 2014. The observations were divided into three types of weather, sunny, rainy and cloudy. The average concentrations of PM2.5 under different weather conditions were sunny > cloudy > rainy days. The concentrations of water soluble ions in PM1.1, PM1.1-2.1 and PM2.1-10 were also sunny > cloudy > rainy days, and the obliterate of fine particles by precipitation process was more obvious. The spectra of Ca2+ and Mg2+ were bimodal. The scavenging effects of SO42- and NH4+ in range of 0.65-1.1 μm were stronger. The ratio of NO3-/SO42- under different weather conditions was less than 1, and the ratio of NO3-/SO42- in rainy and cloudy days was higher than that in sunny days. The values of SOR and NOR in the three kinds of weather conditions were more than 0.1, SO2 and NO2 had different degrees of transformation, there was more secondary pollutant in the atmosphere.

Dust particle flux and size distribution in the coma of 67P/Churyumov-Gerasimenko measured in situ by the COSIMA instrument on board Rosetta

Context. The COmetary Secondary Ion Mass Analyzer (COSIMA) on board Rosetta is dedicated to the collection and compositional analysis of the dust particles in the coma of 67P/Churyumov-Gerasimenko (67P). Aims. Investigation of the physical properties of the dust particles collected along the comet trajectory around the Sun starting at a heliocentric distance of 3.5 AU. Methods. The flux, size distribution, and morphology of the dust particles collected in the vicinity of the nucleus of comet 67P were measured with a daily to weekly time resolution. Results. The particles collected by COSIMA can be classified according to their morphology into two main types: compact particles and porous aggregates. In low-resolution images, the porous material appears similar to the chondritic-porous interplanetary dust particles collected in Earth’s stratosphere in terms of texture. We show that this porous material represents 75% in volume and 50% in number of the large dust particles collected by COSIMA. Compact particles have typical sizes from a few tens of microns to a few hundreds of microns, while porous aggregates can be as large as a millimeter. The particles are not collected as a continuous flow but appear in bursts. This could be due to limited time resolution and/or fragmentation either in the collection funnel or few meters away from the spacecraft. The average collection rate of dust particles as a function of nucleo-centric distance shows that, at high phase angle, the dust flux follows a 1/ d 2 comet law, excluding fragmentation of the dust particles along their journey to the spacecraft. At low phase angle, the dust flux is much more dispersed compared to the 1/ d 2 comet law but cannot be explained by fragmentation of the particles along their trajectory since their velocity, indirectly deduced from the COSIMA data, does not support such a phenomenon. The cumulative size distribution of particles larger than 150 μ m follows a power law close to r − 0.8 ± 0.1 , confirming measurements made by another Rosetta dust instrument Grain Impact Analyser and Dust Accumulator (GIADA). The cumulative size distribution of particles between 30 μ m and 150 μ m has a power index of −1.9 ± 0.3. The excess of dust in the 10–100 μ m range in comparison to the 100 μ m–1 mm range together with no evidence for fragmentation in the inner coma, implies that these particles could have been released or fragmented at the nucleus right after lift-off of larger particles. Below 30 μ m, particles exhibit a flat size distribution. We interprete this knee in the size distribution at small sizes as the consequence of strong binding forces between the sub-constitutents. For aggregates smaller than 30 μ m, forces stronger than Van-der-Waals forces would be needed to break them apart.

The 2016 Feb 19 outburst of comet 67P/CG: an ESA Rosetta multi-instrument study

On 19 Feb. 2016 nine Rosetta instruments serendipitously observed an outburst of gas and dust from the nucleus of comet 67P/Churyumov-Gerasimenko. Among these instruments were cameras and spectrometers ranging from UV over visible to microwave wavelengths, in-situ gas, dust and plasma instruments, and one dust collector. At 9:40 a dust cloud developed at the edge of an image in the shadowed region of the nucleus. Over the next two hours the instruments recorded a signature of the outburst that significantly exceeded the background. The enhancement ranged from 50% of the neutral gas density at Rosetta to factors >100 of the brightness of the coma near the nucleus. Dust related phenomena (dust counts or brightness due to illuminated dust) showed the strongest enhancements (factors >10). However, even the electron density at Rosetta increased by a factor 3 and consequently the spacecraft potential changed from ∼−16 V to −20 V during the outburst. A clear sequence of events was observed at the distance of Rosetta (34 km from the nucleus): within 15 minutes the Star Tracker camera detected fast particles (∼25 m s −1 ) while 100 μm radius particles were detected by the GIADA dust instrument ∼1 hour later at a speed of ~6 m s −1 . The slowest were individual mm to cm sized grains observed by the OSIRIS cameras. Although the outburst originated just outside the FOV of the instruments, the source region and the magnitude of the outburst could be determined.

GIADA – Grain Impact Analyzer and Dust Accumulator – Onboard Rosetta spacecraft: Extended calibrations

Despite a long tradition of dust instruments flown on-board space mission, the largest number of these can be considered unique as they used different detection techniques. GIADA (Grain Impact Analyzer and Dust Accumulator), is one of the dust instruments on-board the Rosetta spacecraft and is devoted to measure the dust dynamical parameters in the coma of comet 67P/Churyumov–Gerasimenko. It couples two different techniques to measure the mass and speed of individual dust particles. We report here the results of an extended calibration activity carried-out, during the hibernation phase of the Rosetta mission, on the GIADA Proto Flight Model (PFM) operative in a clean room in our laboratory. The main aims of an additional calibration campaign are:•to verify the algorithms and procedures for data calibration developed before Rosetta launch;•to improve the comprehension of GIADA response after the increased knowledge on cometary dust, e.g. the composition of dust particles after Stardust mission.These calibration improvements implied a final step, which consisted in defining transfer functions to correlate the new calibration curves obtained for the GIADA PFM to those to be used for GIADA onboard the Rosetta spacecraft. The extended calibration activity allowed us to analyze GIADA data acquired in the 67P/C–G coma permitting to infer additional information on cometary dust particles, e.g. density and tensile strength.

A permanent, asymmetric dust cloud around the Moon.

Interplanetary dust particles hit the surfaces of airless bodies in the Solar System, generating charged and neutral gas clouds, as well as secondary ejecta dust particles. Gravitationally bound ejecta clouds that form dust exospheres were recognized by in situ dust instruments around the icy moons of Jupiter and Saturn, but have hitherto not been observed near bodies with refractory regolith surfaces. High-altitude Apollo 15 and 17 observations of a 'horizon glow' indicated a putative population of high-density small dust particles near the lunar terminators, although later orbital observations yielded upper limits on the abundance of such particles that were a factor of about 10(4) lower than that necessary to produce the Apollo results. Here we report observations of a permanent, asymmetric dust cloud around the Moon, caused by impacts of high-speed cometary dust particles on eccentric orbits, as opposed to particles of asteroidal origin following near-circular paths striking the Moon at lower speeds. The density of the lunar ejecta cloud increases during the annual meteor showers, especially the Geminids, because the lunar surface is exposed to the same stream of interplanetary dust particles. We expect all airless planetary objects to be immersed in similar tenuous clouds of dust.

A new look at Apollo 17 LEAM data: Nighttime dust activity in 1976

One of the unresolved enigmas from the Apollo era is the existence and characteristics of highly electrically charged dust floating above the lunar surface. Potential evidence for this hypothesized phenomenon came from the Lunar Ejecta and Meteorites (LEAM) experiment on Apollo 17. The LEAM instrument consisted of three sets of multi-coincidence dust sensors facing different directions. Recently, new arguments were raised (O'Brien, 2011) that the signals recorded by LEAM may be caused by interferences from heater current switching, which occurred most frequently near sunrise and sunset. In order to shed light on this controversy a new look into the LEAM data was initiated within the Colorado Center for Lunar and Dust and Atmospheric Studies (CCLDAS) team of NASA's Lunar Science Institute (NLSI). The purpose of this analysis is to verify the earlier analysis by Berg et al. (1975), and to find evidence for impacts of interplanetary meteoroids in the LEAM data available to us. A second goal is to find in the LEAM house keeping data evidence for excessive power switching and correlated signals in the LEAM science data. The original analysis by Berg et al. (1975) covered LEAM data during 22 lunations (~22 months) in 1973 and 1974. This data set is no longer available. For the present study, we had access to LEAM data for only about 5 lunations (140 days) in 1976. We analyzed the housekeeping data and observed excessive heating from about 24h after sunrise until about 24h before sunset. We defined sunrise and sunset when the LEAM temperature measurement reached −20°C above which significant solar heating was apparent. For about 9 days around lunar noon the temperatures were so high that LEAM was switched off. During the times of excessive heating LEAM became very noisy. We limit our current analysis to about 24h before sunset to about 24h after sunrise when the LEAM temperatures were moderate <60°C. This carefully analyzed data set of 74.6 days constitutes about 75% of the periods when LEAM was switched on in 1976. We did not find a systematic correlation between the infrequent heater switches and the occurrence of signals. During the lunar night the temperature was quite stable at approx. −25°C. One TOF dust impact event and 19 potential dust events were recorded by all three sensors during the periods when the instrument was at moderate temperatures. This corresponds to an average event rate of 0.25/day. While nine events are compatible with a random occurrence the other 10 events occurred in three statistically significant bursts within about 1h or less after another. Two bursts occurred within the middle of lunar night and one burst of three events was recorded by the West sensor just an hour before sunrise. The background rates are compatible with impact rates recorded by the dust instruments onboard the Pioneer 8 and 9 spacecraft in interplanetary space. Based on our definition of sunrise and sunset, the 1976 LEAM data do not indicate strongly enhanced dust activity at the terminator.

Detection of Interstellar Dust with STEREO/WAVES at 1 AU

Most in situ measurements of cosmic dust have been carried out with dedicated dust instruments. However, dust particles can also be detected with radio and plasma wave instruments. The high velocity impact of a dust particle generates a small crater on the spacecraft, and the dust particle and the crater material are vaporised and partly ionised. The resulting electric charge can be detected with plasma instruments designed to measure electric waves. Since 2007 the STEREO/WAVES instrument has recorded a large number of events due to dust impacts. Here we will concentrate on the study of those impacts produced by dust grains originating from the local interstellar cloud. We present these fluxes during five years of the STEREO mission. Based on model calculations, we determine the direction of arrival of interstellar dust. We find that the interstellar dust direction of arrival is ∼260∘, in agreement with previous studies.

Return to Comet Tempel 1: Overview of Stardust-NExT results

On February 14, 2011 Stardust-NExT (SN) flew by Comet Tempel 1, the target of the Deep Impact (DI) mission in 2005, obtaining dust measurements and high-resolution images of areas surrounding the 2005 impact site, and extending image coverage to almost two thirds of the nucleus surface. The nucleus has an average radius of 2.83±0.1km and a uniform geometric albedo of about 6% at visible wavelengths. Local elevation differences on the nucleus reach up to 830m. At the time of encounter the spin rate was 213° per day (period=40.6h) and the comet was producing some 130kg of dust per second. Some 30% of the nucleus is covered by smooth flow-like deposits and related materials, restricted to gravitational lows. This distribution is consistent with the view that the smooth areas represent material erupted from the subsurface and date from a time after the nucleus achieved its current shape. It is possible that some of these eruptions occurred after 1609 when the comet’s perihelion distance decreased from 3.5AU to the current 1.5AU. Much of the surface displays evidence of layering: some related to the smooth flows and some possibly dating back to the accretion of the nucleus. Pitted terrain covers approximately half the nucleus surface. The pits range up to 850m in diameter. Due to their large number, they are unlikely to be impact scars: rather they probably result from volatile outbursts and sublimational erosion. The DI impact site shows a subdued depression some 50m in diameter implying surface properties similar to those of dry, loose snow. It is possible that the 50-m depression is all that remains of an initially larger crater. In the region of overlapping DI and SN coverage most of the surface remained unchanged between 2005 and 2011 in albedo, photometric properties and morphology. Significant changes took place only along the edges of a prominent smooth flow estimated to be 10–15m thick, the margins of which receded in places by up to 50m. Coma and jet activity were lower in 2011 than in 2005. Most of the jets observed during the SN flyby can be traced back to an apparently eroding terraced scarp. The dust instruments detected bursts of impacts consistent with a process by which larger aggregates of material emitted from the nucleus subsequently fragment into smaller particles within the coma.

Field Monitoring of PM&lt;sub&gt;10&lt;/sub&gt; Dispersion at Street-Canyon Road Intersection

In order to research the harm of particle matter to human health, the TSI dust instrument, particle counter and miniature meteorological instrument were used in this paper to monitor the PM10 concentration of one typical cross road in Xi’an city. The affect factors of the PM10 concentration were also discussed. The results provided that: there is weak linear relationship between sample concentration of PM10 and wind velocity because of the complex shape of the buildings. The fine particles (&lt;1.0μm) mainly come from vehicle emission in the cross road,and the sample concentration of PM10 has a significant relationship with the fine particles under high humidity conditions, while it has weak correlation with traffic flow. The fine particles from vehicle emission and the high humidity condition is the primary cause of the high PM10 concentration, while the temperature and airflow caused by the building shape affect the diffusion and distribution of the PM10.

Galileo dust data from the jovian system: 2000 to 2003

The Galileo spacecraft was the first man-made satellite of Jupiter, orbiting the planet between December 1995 and September 2003. The spacecraft was equipped with a highly sensitive dust detector that monitored the jovian dust environment between approximately 2 and 370 R J (jovian radius R J=71 492 km). The Galileo dust detector was a twin of the one flying on board the Ulysses spacecraft. This is the tenth in a series of papers dedicated to presenting Galileo and Ulysses dust data. Here we present data from the Galileo dust instrument for the period January 2000 to September 2003 until Galileo was destroyed in a planned impact with Jupiter. The previous Galileo dust data set contains data of 2883 particles detected during Galileo's interplanetary cruise and 12 978 particles detected in the jovian system between 1996 and 1999. In this paper we report on the data of additional 5389 particles measured between 2000 and the end of the mission in 2003. The majority of the 21 250 particles for which the full set of measured impact parameters (impact time, impact direction, charge rise times, charge amplitudes, etc.) was transmitted to Earth were tiny grains (about 10 nm in radius), most of them originating from Jupiter's innermost Galilean moon Io. They were detected throughout the jovian system and the impact rates frequently exceeded 10 min −1. Surprisingly large impact rates up to 100 min −1 occurred in August/September 2000 when Galileo was far away ( ≈ 280 R J ) from Jupiter, implying dust ejection rates in excess of 100 kg s −1. This peak in dust emission appears to coincide with strong changes in the release of neutral gas from the Io torus. Strong variability in the Io dust flux was measured on timescales of days to weeks, indicating large variations in the dust release from Io or the Io torus or both on such short timescales. Galileo has detected a large number of bigger micron-sized particles mostly in the region between the Galilean moons. A surprisingly large number of such bigger grains was measured in March 2003 within a four-day interval when Galileo was outside Jupiter's magnetosphere at approximately 350 R J jovicentric distance. Two passages of Jupiter's gossamer rings in 2002 and 2003 provided the first actual comparison of in-situ dust data from a planetary ring with the results inferred from inverting optical images. Strong electronics degradation of the dust instrument due to the harsh radiation environment of Jupiter led to increased calibration uncertainties of the dust data.