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The lower reaches of the Yajiang River are high in the east and low in the west, with abundant rainfall, and contain a large amount of hydropower resources that have not been exploited and utilized. Nonetheless, due to the unique geographical environment in southeast Tibet, rainfall debris flow is one of the frequent geological disasters in this area. In this research, 42 debris flow points were collected, ten disaster-causing factors were selected, and satellite elevation data were analyzed to evaluate the disaster susceptibility of the study area. The disaster-causing factors information is extracted from Arcgis. The certainty factor model (CF) was used to calculate the coefficient of certainty of 10 factors including fault distance, elevation, normalized difference vegetation index (NDVI), average annual rainfall, profile curvature, relief, silt content, TWI, SPI, and slope aspect. The Analytic Hierarchy Process (AHP), Binary Logistic Regression (LR), Random Forest (RF) and CF model were used to analyze and predict the possibility of debris flow occurrence. The results show that the accuracy of the CF-LR model is the highest under the verification of the ROC curve. In the prediction model, the high-risk areas of debris flow are mainly concentrated in the first half of the lower reaches of the Yajiang River and distributed along both sides of the river bank. After bringing the data of different annual rainfall into the model, it is found that the saturation critical value of debris flow water source in the study area is within the range of 600–700mm annual rainfall. [ABSTRACT FROM AUTHOR]

In recent year, flood becomes a serious issue in Tibetan Plateau (TP) due to climate change. Many studies have shown that ensemble flood forecasting based on numerical weather predictions can provide early warning with extended lead time. However, the role of hydrological ensemble prediction in forecasting flood volume and its components over the Yarlung Zangbo River Basin (YZR), China has not been systematically investigated. This study adopts Variable Infiltration Capacity (VIC) model to forecast annual maximum floods (MF) and annual first floods (FF) in YZR based on precipitation, maximum and minimum temperature from European Centre for Medium-Range Weather Forecasts (ECMWF). N-simulations is proposed to account for more scenarios of parameters in VIC and shows improved flood simulation. Ensemble flood forecasting system can skilfully predict MF with a lead time of more than10 days, and has skill in forecasting the snowmelt-related components in about 7 days ahead. The accuracy of forecasts for FF is inferior with a lead time of only 5 days. The performance in 7-day accumulated flood volumes is better than the peak flows. The components in baseflow for FF are irrelevant to lead time, whilst for MF an obvious deterioration in performance with lead time can be perceived. The snowmelt-induced surface runoff is the most poorly captured component by the system, and the well-predicted rainfall-related components are the major contributor for good performance. From this study, it is concluded that snowmelt-induced flood volume plays an important role in YZR Basin especially in FF. [ABSTRACT FROM AUTHOR]

The emission, dispersion and photochemistry of isoprene (C5H8) and related chemical species in the convective boundary layer (CBL) during sunlit daytime was studied over a mixed forest in the Southeast United States by combining ground-based and aircraft 5 observations. Fluxes of isoprene and monoterpenes were quantified at the top of the forest canopy using a high resolution Proton Transfer Reaction Time of Flight Mass Spectrometer (PTR-TOF-MS). Snapshot (~ 2min sampling duration) vertical profiles of isoprene, methyl vinyl ketone (MVK) + methacrolein (MACR), and monoterpenes were collected from aircraft every hour in the CBL (100-1000 m). Both ground-based and air10 borne collected volatile organic compound (VOC) data are used to constrain the initial conditions of a mixed layer chemistry model (MXLCH), which is applied to examine the chemical evolution of the O3-NOx-HOx-VOC system and how it is affected by boundary layer dynamics in the CBL. The chemical loss rate of isoprene (~ 1h) is similar to the turbulent mixing time scale (0.1-0.5 h), which indicates that isoprene concen15 trations are equally dependent on both photo-oxidation and boundary layer dynamics. Analysis of a model-derived concentration budget suggests that diurnal evolution of isoprene inside the CBL is mainly controlled by surface emissions and chemical loss. The NO to HO2 ratio (NO :HO2) is used as an indicator of anthropogenic impact on the CBL chemical composition, and spans a wide range (1-163). The fate of hydroxylsubstituted isoprene peroxyl radical (HOC5H8OO q 20 ; ISOPOO) is strongly affected by NO:HO2, shifting from NO-dominant to NO-HO2-balanced condition from early morning to noontime. This chemical regime change is reflected in the diurnal evolution of isoprene hydroxynitrates (ISOPN) and isoprene hydroxy hydroperoxides (ISOPOOH). [ABSTRACT FROM AUTHOR]

The principles of cloud droplet size retrieval via Polarization and Directionality of the Earth's Re- flectance (POLDER) requires that clouds be horizontally homogeneous. The retrieval is performed by combining all measurements from an area of 150 km x 150 km to compensate for POLDER's insufficient directional sampling. Using POLDER-like data simulated with the RT3 model, we investigate the impact of cloud horizontal inhomogeneity and directional sampling on the retrieval and analyze which spatial resolution is potentially accessible from the measurements. Case studies show that the sub-grid-scale variability in droplet effective radius (CDR) can significantly reduce valid retrievals and introduce small biases to the CDR (~1.5 µm) and effective variance (EV) estimates. Nevertheless, the sub-grid-scale variations in EV and cloud optical thickness (COT) only influence the EV retrievals and not the CDR estimate. In the directional sampling cases studied, the retrieval using limited observations is accurate and is largely free of random noise. Several improvements have been made to the original POLDER droplet size retrieval. For example, measurements in the primary rainbow region (137-145°) are used to ensure retrievals of large droplet (> 15 µm) and to reduce the uncertainties caused by cloud heterogeneity. We apply the improved method using the POLDER global L1B data from June 2008, and the new CDR results are compared with the operational CDRs. The comparison shows that the operational CDRs tend to be underestimated for large droplets because the cloudbow oscillations in the scattering angle region of 145-165° are weak for cloud fields with CDR> 15 µm. Finally, a sub-grid-scale retrieval case demonstrates that a higher resolution, e.g., 42 km x 42 km, can be used when inverting cloud droplet size distribution parameters from POLDER measurements. [ABSTRACT FROM AUTHOR]

The principles of the Polarization and Directionality of the Earth's Reflectance (POLDER) cloud droplet size retrieval requires that clouds are horizontally homogeneous. Nevertheless, the retrieval is applied by combining all measurements from an area of 150 km × 150 km to compensate for POLDER's insufficient directional sampling. Using the POLDER-like data simulated with the RT3 model, we investigate the impact of cloud horizontal inhomogeneity and directional sampling on the retrieval, and then analyze which spatial resolution is potentially accessible from the measurements. Case studies show that the sub-scale variability in droplet effective radius (CDR) can mislead both the CDR and effective variance (EV) retrievals. Nevertheless, the sub-scale variations in EV and cloud optical thickness (COT) only influence the EV retrievals and not the CDR estimate. In the directional sampling cases studied, the retrieval is accurate using limited observations and is largely independent of random noise. Several improvements have been made to the original POLDER droplet size retrieval. For example, the measurements in the primary rainbow region (137-145°) are used to ensure accurate large droplet (> 15 µm) retrievals and reduce the uncertainties caused by cloud heterogeneity. We apply the improved method using the POLDER global L1B data for June 2008, the new CDR results are compared with the operational CDRs. The comparison show that the operational CDRs tend to be underestimated for large droplets. The reason is that the cloudbow oscillations in the scattering angle region of 145-165° are weak for cloud fields with CDR > 15 µm. Lastly, a sub-scale retrieval case is analyzed, illustrating that a higher resolution, e.g., 42 km × 42 km, can be used when inverting cloud droplet size parameters from POLDER measurements. [ABSTRACT FROM AUTHOR]

Theα-dicarbonyl compounds glyoxal (CHOCHO) and methyl glyoxal (CH3C(O)CHO) are produced in the atmosphere by the oxidation of hydrocarbons and emitted directly from pyrogenic sources. Measurements of ambient concentrations inform about the rate of hydrocarbon oxidation, oxidative capacity, and secondary organic aerosol (SOA) formation. We present results from a comprehensive instrument comparison effort at two simulation chamber facilities in the US and Europe that included nine instruments, and seven different measurement techniques: broadband cavity enhanced absorption spectroscopy (BBCEAS), cavity-enhanced differential optical absorption spectroscopy (CE-DOAS), white-cell DOAS, Fourier transform infrared spectroscopy (FTIR, two separate instruments), laser-induced phosphorescence (LIP), solid-phase micro extraction (SPME), and proton transfer reaction mass spectrometry (PTR-ToF-MS, two separate instruments; for methyl glyoxal only because no significant response was observed for glyoxal). Experiments at the National Center for Atmospheric Research (NCAR) compare three independent sources of calibration as a function of temperature (293- 330 K). Calibrations from absorption cross-section spectra at UV-visible and IR wavelengths are found to agree within 2% for glyoxal, and 4% for methyl glyoxal at all temperatures; further calibrations based on ion-molecule rate constant calculations agreed within 5% for methyl glyoxal at all temperatures. At the European Photoreactor (EUPHORE) all measurements are calibrated from the same UV-visible spectra (either directly or indirectly), thus minimizing potential systematic bias. We find excellent linearity under idealized conditions (pure glyoxal or methyl glyoxal, R2 > 0:96), and in complex gas mixtures characteristic of dry photochemical smog systems (o-xylene/NOx and isoprene/NOx, R2 > 0:95; R2 ~ 0:65 for offline SPME measurements of methyl glyoxal). The correlations are more variable in humid ambient air mixtures (RH>45 %) for methyl glyoxal (0:58 < R2 < 0:68) than for glyoxal (0:79 < R2 < 0:99). The intercepts of correlations were insignificant for the most part (below the instruments' experimentally determined detection limits); slopes further varied by less than 5% for instruments that could also simultaneously measure NO2. For glyoxal and methyl glyoxal the slopes varied by less than 12 and 17% (both 3-σ) between direct absorption techniques (i.e., calibration from knowledge of the absorption cross section). We find a larger variability among in situ techniques that employ external calibration sources (75-90 %, 3-σ), and/or techniques that employ offline analysis. Our intercomparison reveals existing differences in reports about precision and detection limits in the literature, and enables comparison on a common basis by observing a common air mass. Finally, we evaluate the influence of interfering species (e.g., NO2, O3 and H2O) of relevance in field and laboratory applications. Techniques now exist to conduct fast and accurate measurements of glyoxal at ambient concentrations, and methyl glyoxal under simulated conditions. However, techniques to measure methyl glyoxal at ambient concentrations remain a challenge, and would be desirable. [ABSTRACT FROM AUTHOR]

Atmospheric particulate matter (PM) remains poorly understood due to the lack of comprehensive measurements at high time resolution for tracking its dynamic features and the lack of long-term observation for tracking its seasonal variability. Here, we present highly time resolved and seasonal compositions and characteristics of non-refractory components in PM with a diameter less than 1 μm (NR-PM1) at a suburban site in Hong Kong. The measurements were made with an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) at the Hong Kong University of Science and Technology (HKUST) Air Quality Research Supersite for 4 months, with one in each season of the year. The average NR-PM1 concentration of ~15pgm-3 is higher than those AMS measurements made in South Korea and Japan, but lower than those in North China, the Yangtze River Delta and the nearby Pearl River Delta. The seasonal dependence of the total NRPM1 monthly averaged concentrations was small, but that of the fractions of the species in NR-PM1 was significant. Site characteristic plays an important role in the relative fractions of species in NR-PM1 and our results are generally consistent with measurements at other non-urban sites in this regard. Detailed analyses were conducted on the AMS data in the aspects of (1) species concentrations, (2) size distributions, (3) degree of oxygenation of organics, and (4) positive matrix factorization (PMF)-resolved organic factors in a seasonal context, as well as with air mass origin from back-trajectory analysis. Sulfate had the highest fraction in NR-PM1 (>40%), and the surrogates of secondary organic species - semi-volatile oxygenated organic aerosol (SVOOA) and low-volatility oxygenated organic aerosol (LVOOA) - prevailed (~80%) in the organic portion of NRPM1. Local contributions to the organic portion of NR-PM1 at this suburban site was strongly dependent on season. The hydrocarbon-like organic aerosol (HOA) factor related to local traffic emissions contributed > 10% to organic aerosols in spring and summer but only 6-7% in autumn and winter. The cooking organic aerosol (COA) factor contributed >10% to organic aerosols in winter. With the aid of highly time-resolved data, diurnal patterns of the degree of oxygenation of organic aerosols were used to determine the sources and formation processes of the least understood organic portion of PM. The oxygen-to-carbon atomic ratio (O : C) and average carbon oxidation state (OSC) showed little variation in autumn and winter, when the long-range transport of oxidized organics dominated, whereas they peaked in the afternoon in spring and summer, when locally produced secondary organic aerosol prevailed. Air mass origin, in contrast, had a strong influence on both NR-PM1 concentrations and the fractions of species in NR-PM1. The findings of the current study provide a better understanding of the role of air mass origin in the seasonal characteristics of the PM composition and the relative importance of local vs. transported organic aerosols in this region. [ABSTRACT FROM AUTHOR]

An in-house developed mobile and portable threedimensional scanning lidar system is discussed in this work. The system uses a stimulated Raman-scattering technique for the continuous observation of atmospheric aerosols, clouds and trace gases. This system has a fast scanning technique with a high-speed data acquisition, and permits the real-time measurement of atmospheric pollutants with the temporal resolution of 1 min. This scanning lidar system provides typical horizontal coverage of about 8-10 km while scanning; however, in zenith mode, good quality backscattered signals can be from 20 km, depending upon the laser power and sky conditions. This versatile lidar system has also overcome the drawbacks which are popular in the traditional scanning lidar systems such as complicated operation, overlap height between laser beam and telescope field of view In this system, the optical damage is reduced by using an integral coaxial transmitter and receiver. Some of the initial results obtained from the scanning lidar system are also presented. This study shows that boundary-layer structure and land-sea breeze circulation can be resolved from the developed scanning lidar system. The application of this lidar system to measure the pollutants over an industrial area is also discussed. [ABSTRACT FROM AUTHOR]

Atmospheric particulate matter (PM) remains poorly understood due to the lack of comprehensive measurements at high time resolution for tracking its dynamic features and the lack of long-term observation for tracking its seasonal variability. Here, we present highly time-resolved and seasonal compositions and characteristics of non-refractory components in PM with diameter less than 1 μm (NR-PM1) at a suburban site in Hong Kong. The measurements were made with an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) at the Hong Kong University of Science and Technology (HKUST) Air Quality Research Supersite for four months, with one in each season of the year. The average NR-PM1 concentration of ~ 15 µg m³ is higher than those AMS measurements made in South Korea and Japan, but lower than those in North China, the Yangtze River Delta and the nearby Pearl River Delta. The seasonal dependence of the total NR-PM1 monthly averaged concentrations was small but that of the fractions of the species in NR-PM1 was significant. Site characteristic plays an important role in the relative fractions of species in NR-PM1 and our results are generally consistent with measurements at other non-urban sites in this regard. Detailed analyses were conducted on the AMS data in the aspects of (1) species concentrations, (2) size distributions, (3) degree of oxygenation of organics, and (4) positive matrix factorization (PMF)-resolved organic factors in a seasonal context, as well as with air mass origin from back-trajectory analysis. Sulfate had the highest fraction in NR-PM1 (>40%) and the surrogates of secondary organic species, semi-volatile oxygenated organic aerosol (SVOOA) and low-volatility oxygenated organic aerosol (LVOOA), prevailed (~80%) in the organic portion of NR-PM1. Local contributions to the organic portion of NR-PM1 at this suburban site was strongly dependent on season. The hydrocarbon-like organic aerosol (HOA) factor related to local traffic emissions contributed > 10% to organic aerosols in spring and summer, but only 6-7% in autumn and winter. The cooking organic aerosol (COA) factor contributed > 10% to organic aerosols in winter. With the aid of highly time-resolved data, diurnal patterns of the degree of oxygenation of organic aerosols were used to determine the sources and formation processes of the least understood organic portion of PM. The oxygen-to-carbon atomic ratio (O : C) and average carbon oxidation state (...C) showed little variation in autumn and winter when the long-range transport of oxidized organics dominated, whereas they peaked in the afternoon in spring and summer when locally produced secondary organic aerosol prevailed. Air mass origin, in contrast, had a strong influence on both NR-PM1 concentrations and the fractions of species in NR-PM1. The findings of the current study provide a better understanding of the role of air mass origin in the seasonal characteristics of the PM composition and the relative importance of local vs. transported organic aerosols in this region. [ABSTRACT FROM AUTHOR]

An in-house developed mobile and portable threedimensional scanning lidar system is discussed in this work. The system uses a stimulated Raman-scattering technique for the continuous observation of atmospheric aerosols, clouds and trace gases. This system has a fast scanning technique with a high-speed data acquisition, and permits the real-time measurement of atmospheric pollutants with the temporal resolution of 1 min. This scanning lidar system provides typical horizontal coverage of about 8–10 km while scanning; however, in zenith mode, good quality backscattered signals can be from 20 km, depending upon the laser power and sky conditions. This versatile lidar system has also overcome the drawbacks which are popular in the traditional scanning lidar systems such as complicated operation, overlap height between laser beam and telescope field of view In this system, the optical damage is reduced by using an integral coaxial transmitter and receiver. Some of the initial results obtained from the scanning lidar system are also presented. This study shows that boundary-layer structure and land–sea breeze circulation can be resolved from the developed scanning lidar system. The application of this lidar system to measure the pollutants over an industrial area is also discussed. [ABSTRACT FROM AUTHOR]

The emission and fate of reactive volatile organic compounds (VOCs) is of inherent interest to those studying chemical biosphere-atmosphere interactions. In-canopy VOC observations are obtainable using tower-based samplers, but the lack of suitable sampling systems for the full boundary layer has limited the availability of data characterizing the vertical structure of such gases above the canopy height and still in the boundary layer. This is an important region where many reactive VOCs are oxidized or otherwise removed. Here we describe an airborne sampling system designed to collect a vertical profile of air into a 3/8 in. OD (outer diameter) tube 150m in length. The inlet ram air pressure is used to flow sampled air through the tube, which results in a varying flow rate based on aircraft speed and altitude. Since aircraft velocity decreases during ascent, it is necessary to account for the variable flow rate into the tube. This is accomplished using a reference gas that is pulsed into the air stream so that the precise altitude of the collected air can be reconstructed post-collection. The pulsed injections are also used to determine any significant effect from diffusion/ mixing within the sampling tube, either during collection or subsequent extraction for gas analysis. This system has been successfully deployed, and we show some measured vertical profiles of isoprene and its oxidation products methacrolein and methyl vinyl ketone from a mixed canopy near Columbia, Missouri. [ABSTRACT FROM AUTHOR]

The article reports on the study that develops two correction approaches for the row anomaly effects in the northern latitudes and along the full orbit. It states that the approaches aimed at imrpoving global measurements of atmospheric sulfur dioxide from the Ozone Monitoring Instrument (OMI). It indicates that the consistencies among the sulfur columns inside and outside the row anomaly areas have demonstrated the effectiveness of the correction approaches under row anomaly conditions.

Atmospheric aerosols affect both human health and climate. PMX is the mass concentration of aerosol particles that have aerodynamic diameters less than Xµm, PM10 was initially selected to measure the environmental impact of aerosols. Recently, it was realized that fine particles are more hazardous than larger ones and should be measured. Consequently, observational data for PM2.5 have been obtained but only for a much shorter period than that of PM10. Optical extinction of aerosols, the inverse of meteorological visibility, is sensitive to particles less than 1.0 µm. These fine particles only account for a small part of total mass of aerosols although they are very efficient in light extinction. Comparisons are made between PM10 and PM2.5 over the period when the latter is available and with visibility data for a longer period. PM10 has decreased by 44% in Europe from 1992 to 2009, 33% in the US from 1993 to 2010, 10% in Canada from 1994 to 2009, and 26% in China from 2000 to 2011. However, in contrast, aerosol optical extinction has increased 7% in the US, 10% in Canada, and 18% in China during the above study periods. The reduction of optical extinction over Europe of 5% is also much less than the 44% reduction in PM10. Over its short period of record PM2.5 decreased less than PM10. Hence, PM10 is neither a good measure of changes in smaller particles nor of their long-term trends, a result that has important implications for both climate impact and human health effects. The increased fraction of anthropogenic aerosol emission, such as from vehicle exhaust, to total atmospheric aerosols partly explains this contrasting trend of optical and mass properties of aerosols. [ABSTRACT FROM AUTHOR]

The article presents a study which looks into the main noise sources and the best residual adjustment area of Ozone Monitoring Instrument (OMI) sulfur dioxide (SO2). The study analyzes various residual correction effects of OMI SO2. It also describes the optimization of the Band Residual Difference (BRD) algorithm for data noise and cites existing retrieval error sources.

This study compares the properties of atmospheric dust from the Saharan deserts and the Asian deserts using data from CALIPSO and AERONET during 2006 and 2007 along with simulations using a coupled climate-microphysical sectional model. Saharan deserts are largely south of 30° N, while Asian ones are primarily north of 30° N, hence they experience different meteorological regimes. Saharan dust lifting occurs all year long, primarily due to subtropical weather systems. However, Asian dust is lifted mostly in spring when mid-latitude frontal systems lead to high winds. Rainfall is more abundant over Asia during the dust lifting events, leading to greater local dust removal than over the Sahara. However, most dust removal is due to sedimentation. Despite the different meteorological regimes, the same dust lifting schemes work in models for Asian and Saharan dust. The magnitudes of dust lifted in Africa and Asia differ significantly over the year. In our model the yearly horizontal dust flux just downwind of the African dust source is about 1088Tg (10° S-40° N, 10° W) and from the Asian dust source it is about 355Tg (25° N-55° N, 105° E) in 2007, which is comparable to previous studies. We find the difference in dust flux is mainly due to the larger area over which dust is lifted in Africa than Asia. However, Africa also has stronger winds in some seasons. Once lifted, the Saharan dust layers generally move toward the west and descend in altitude from about 7 km to the surface over several days in the cases studied. Asian dust often has multiple layers (two layers in the cases studied) during transport largely to the east. One layer stays well above boundary layer during transport and shows little descent, while the other, lower, layer descends with time. This observation contrasts with studies suggesting the descent of Saharan dust is due to sedimentation of the particles, and suggests instead it is dominated by meteorology. We find the size distributions of Asian and African dust are similar when the dust is lifted, but the mode size can differ and secondary size modes can develop probably due to differences in vertical wind velocities during transport. The single scattering albedo of African and Asian dust does differ, due primarily to the imaginary parts of the refractive indexes being different, which in turn is likely due to different dust composition. This study is a step towards a global understanding of dust and its properties. [ABSTRACT FROM AUTHOR]

This study compares the properties of atmospheric dust from the Saharan deserts and the Asian deserts using data from CALIPSO and AERONET during 2006 and 2007 along with simulations using a coupled climate-microphysical sectional model. Saharan deserts are largely south of 30° N, while Asian ones are primarily north of 30° N, hence they experience different meteorological regimes. Saharan dust lifting occurs all year long, primarily due to subtropical weather systems. However, Asian dust is lifted mostly in spring when mid-latitude frontal systems lead to high winds. Rainfall is more abundant over Asia during the dust lifting events, leading to greater local dust removal than over the Sahara. However, most dust removal is due to sedimentation. Despite the different meteorological regimes, the same dust lifting schemes work in models for Asian and Saharan dust. The magnitudes of dust lifted in Africa and Asia differ significantly over the year. In our model the yearly horizontal dust flux just downwind of the African dust source is about 1446 Tg (10° S-40° N, 10° E) and from the Asian dust source it is about 355Tg (25° N-55° N, 105° E) in 2007, which is comparable to previous studies. We find the difference in dust flux is mainly due to the larger area over which dust is lifted in Africa than Asia. However, Africa also has stronger winds in some seasons. Once lifted, the Saharan dust layers generally move toward the west and descend in altitude from about 7 km to the surface over several days in the cases studied. Asian dust often has multiple layers (two layers in the cases studied) during transport largely to the east. One layer stays well above boundary layer during transport and shows little descent, while the other, lower, layer descends with time. This observation contrasts with studies suggesting the descent of Saharan dust is due to sedimentation of the particles, and suggests instead it is dominated by meteorology. We find the size distributions of Asian and African dust are similar when the dust is lifted, but the mode size can differ and secondary size modes can develop due to differences in vertical wind velocities during transport. The single scattering albedo of African and Asian dust does differ, due primarily to the imaginary parts of the refractive indexes being different, which in turn is likely due to different dust composition. This study is a step towards a global understanding of dust and its properties. [ABSTRACT FROM AUTHOR]