Columnar Aerosol Research Articles

Performance of WRF-Chem over Indian region: Comparison with measurements

The aerosol mass concentrations over several Indian regions have been simulated using the online chemistry transport model, WRF-Chem, for two distinct seasons of 2011, representing the pre-monsoon (May) and post-monsoon (October) periods during the Indo–US joint experiment ‘Ganges Valley Aerosol Experiment (GVAX)’. The simulated values were compared with concurrent measurements. It is found that the model systematically underestimates near-surface BC mass concentrations as well as columnar Aerosol Optical Depths (AODs) from the measurements. Examining this in the light of the model-simulated meteorological parameters, we notice the model overestimates both planetary boundary layer height (PBLH) and surface wind speeds, leading to deeper mixing and dispersion and hence lower surface concentrations of aerosols. Shortcoming in simulating rainfall pattern also has an impact through the scavenging effect. It also appears that the columnar AODs are influenced by the unrealistic emission scenarios in the model. Comparison with vertical profiles of BC obtained from aircraft-based measurements also shows a systematic underestimation by the model at all levels. It is seen that concentration of other aerosols, viz., dust and sea-salt are closely linked with meteorological conditions prevailing over the region. Dust is higher during pre-monsoon periods due to the prevalence of north-westerly winds that advect dust from deserts of west Asia into the Indo-Gangetic plain. Winds and rainfall influence sea-salt concentrations. Thus, the unrealistic simulation of wind and rainfall leads to model simulated dust and sea-salt also to deviate from the real values; which together with BC also causes underperformance of the model with regard to columnar AOD. It appears that for better simulations of aerosols over Indian region, the model needs an improvement in the simulation of the meteorology.

One year of Raman lidar observations of free-tropospheric aerosol layers over South Africa

Abstract. Raman lidar data obtained over a 1 year period has been analysed in relation to aerosol layers in the free troposphere over the Highveld in South Africa. In total, 375 layers were observed above the boundary layer during the period 30 January 2010 to 31 January 2011. The seasonal behaviour of aerosol layer geometrical characteristics, as well as intensive and extensive optical properties were studied. The highest centre heights of free-tropospheric layers were observed during the South African spring (2520 ± 970 m a.g.l., also elsewhere). The geometrical layer depth was found to be maximum during spring, while it did not show any significant difference for the rest of the seasons. The variability of the analysed intensive and extensive optical properties was high during all seasons. Layers were observed at a mean centre height of 2100 ± 1000 m with an average lidar ratio of 67 ± 25 sr (mean value with 1 standard deviation) at 355 nm and a mean extinction-related Ångström exponent of 1.9 ± 0.8 between 355 and 532 nm during the period under study. Except for the intensive biomass burning period from August to October, the lidar ratios and Ångström exponents are within the range of previous observations for urban/industrial aerosols. During Southern Hemispheric spring, the biomass burning activity is clearly reflected in the optical properties of the observed free-tropospheric layers. Specifically, lidar ratios at 355 nm were 89 ± 21, 57 ± 20, 59 ± 22 and 65 ± 23 sr during spring (September–November), summer (December–February), autumn (March–May) and winter (June–August), respectively. The extinction-related Ångström exponents between 355 and 532 nm measured during spring, summer, autumn and winter were 1.8 ± 0.6, 2.4 ± 0.9, 1.8 ± 0.9 and 1.8 ± 0.6, respectively. The mean columnar aerosol optical depth (AOD) obtained from lidar measurements was found to be 0.46 ± 0.35 at 355 nm and 0.25 ± 0.2 at 532 nm. The contribution of free-tropospheric aerosols on the AOD had a wide range of values with a mean contribution of 46%.

Identification of aerosol types over an urban site based on air-mass trajectory classification

Columnar aerosol properties retrieved from MICROTOPS II Sun Photometer measurements during 2010–2013 over Pune (18°32′N; 73°49′E, 559m amsl), a tropical urban station in India, are analyzed to identify aerosol types in the atmospheric column. Identification/classification is carried out on the basis of dominant airflow patterns, and the method of discrimination of aerosol types on the basis of relation between aerosol optical depth (AOD500nm) and Ångström exponent (AE, α). Five potential advection pathways viz., NW/N, SW/S, N, SE/E and L have been identified over the observing site by employing the NOAA-HYSPLIT air mass back trajectory analysis. Based on AE against AOD500nm scatter plot and advection pathways followed five major aerosol types viz., continental average (CA), marine continental average (MCA), urban/industrial and biomass burning (UB), desert dust (DD) and indeterminate or mixed type (MT) have been identified. In winter, sector SE/E, a representative of air masses traversed over Bay of Bengal and Eastern continental Indian region has relatively small AOD (τpλ=0.43±0.13) and high AE (α=1.19±0.15). These values imply the presence of accumulation/sub-micron size anthropogenic aerosols. During pre-monsoon, aerosols from the NW/N sector have high AOD (τpλ=0.61±0.21), and low AE (α=0.54±0.14) indicating an increase in the loading of coarse-mode particles over Pune. Dominance of UB type in winter season for all the years (i.e. 2010–2013) may be attributed to both local/transported aerosols. During pre-monsoon seasons, MT is the dominant aerosol type followed by UB and DD, while the background aerosols are insignificant.

Satellite Derived Aerosol Optical Depth Climatology over Tropical Coastal Station Machilipatnam, India

Climatological aerosol optical depths (AOD) over Tropical coastal city Machilipatnam, India have been examined to bring out the temporal heterogeneity in columnar aerosol characteristics. AOD values at 388 nm derived from the Ozone Monitoring Instrument (OMI) sensor EOS-AURA satellite, for the period of 2005–2013 have been analyzed for the purpose. AOD trends exhibited seasonal annual mean variations. Frequency distributions of the AOD values are examined to infer the monthly mean values. Monthly and seasonal variations of AOD are investigated in the light of regional synoptic meteorology. AODs>0.6 showed maximum occurrence in monsoon months. The mean AOD values increased towards summer reaching ~0.69 ± 0.34 and attained peak in monsoon season with a value of ~0.74 ± 0.33 and decreased during post-monsoon reaching as low as ~0.73 ± 0.3. Positive slope ~0.016 observed for inter annual distribution trend line. Factors like synoptic scale circulation patterns which are causing modulations of AOD apart from local sources were discussed.

Satellite Derived Aerosol Optical Depth Climatology over Tropical Coastal Station Machilipatnam, India

Climatological aerosol optical depths (AOD) over Tropical coastal city Machilipatnam, India have been examined to bring out the temporal heterogeneity in columnar aerosol characteristics. AOD values at 388 nm derived from the Ozone Monitoring Instrument (OMI) sensor EOS-AURA satellite, for the period of 2005–2013 have been analyzed for the purpose. AOD trends exhibited seasonal annual mean variations. Frequency distributions of the AOD values are examined to infer the monthly mean values. Monthly and seasonal variations of AOD are investigated in the light of regional synoptic meteorology. AODs>0.6 showed maximum occurrence in monsoon months. The mean AOD values increased towards summer reaching ~0.69 ± 0.34 and attained peak in monsoon season with a value of ~0.74 ± 0.33 and decreased during post-monsoon reaching as low as ~0.73 ± 0.3. Positive slope ~0.016 observed for inter annual distribution trend line. Factors like synoptic scale circulation patterns which are causing modulations of AOD apart from local sources were discussed.

Processing ores and anthropogenic Cu-Ni feedstock with the application of technology of jet air-steam flotation

A method of flotation is investigated in which a mixture of air with saturated water steam is used as a gas phase. When steam contacts liquid, the boundary layer of the bubble is heated due to the heat of condensation, which is further spent for steam evaporation—the bubble is broadened and forces out the “hot” layer from the surface into the bulk, while its place is occupied by underheated liquid and condensation repeats. The wavelike repetition of condensation ↔ evaporation processes determines the damping pulsations of the bubble surface, which varies the result of flotation. The flotation method by the air-steam mixture is used when concentrating the copper-nickel feedstock by the scheme “in two jets”: the crude concentrate of the first flotation jet is isolated from 1/2 part of the initial feedstock, it is mixed with another 1/2 part of the ore, and the ready crude concentrate of the second flotation jet is isolated using aerosol column flotation. When concentrating the ores of the Pechenga region (Russia) by the flow chart with the jet motion of the initial feeding and crude concentrate with the application of the air-steam mixture as the gas phase during the flotation, the increment in recovery of nickel was 2.93% and that of copper was 3.22%. The passage to the technology of jet air-steam flotation when concentrating dump slags of OAO MMC Norilsk Nickel led to an increase in recovery of nickel from 45.94 to 47.34% and of copper from 78.27 to 82.77%.

PROCESSING ORES AND ANTHROPOGENIC CU–NI FEEDSTOCK WITH THE APPLICATION OF TECHNOLOGY OF JET AIR–STEAM FLOTATION

A method of flotation investigated, for which a mixture of air with saturated water steam is used as a gas phase. When steam contacts with liquid, the boundary layer of the bubble is heated due to heat of condensation, which is further spent for steam evaporation—the bubble is broadened and forces out the «hot» layer from the surface into the bulk, while its place is occupied by underheated liquid, and condensation repeats. The wave-like repetition of condensation↔evaporation processes determines the damping pulsations of the bubble surface, which varies the result of flotation. The flotation method by the air-steam mixture is used when concentrating the copper–nickel feedstock by the scheme «in two jets»: the crude concentrate of the first flotation jet is isolated from 1/2 part of the initial feedstock, it is mixed with another 1/2 part of ore, and ready crude concentrate of the second flotation jet is isolated using aerosol column flotation. When concentrating the ores of the Pechenga ratio (Russia) by the flow chart with the jet motion of the initial feeding and crude concentrate with the application of the air-steam mixture as the gas phase during the flotation, an increment in recovery of nickel was 2,93 % and copper – 3,22 %. The passage to the technology of jet air-steam flotation when concentrating dump slags of OAO MMC «Norilsk Nickel» led to an increase in recovery of nickel from 45,94 to 47,34 % and copper from 78,27 to 82,77 %.

Spatiotemporal coherence of mean and extreme aerosol particle events over eastern North America as observed from satellite

Quantifying spatiotemporal scales of coherence and variability of aerosol particle properties provides (i) metrics for evaluating observational data sets and model simulations, (ii) inferences regarding dominant causes of variability, and (iii) information that is necessary to determine their climate forcing and air quality impacts. Accordingly, analyses of columnar aerosol optical depth (AOD) and Ångström exponent (AE) from the MODerate resolution Imaging Spectroradiometer (MODIS) on the Aqua and Terra satellites, and AErosol RObotic NETwork (AERONET) stations are used to evaluate the spatially averaged (Level-3) MODIS products, and to characterize the spatiotemporal scales of variability (and coherence) of aerosol particles over eastern North America (2000–2013). Results show a high degree of consistency in AOD retrievals from the different data sets but larger discrepancies in AE estimates, highest mean AOD and lowest day-to-day variability during the summer, and largest scales of spatial coherence in summer and fall. Consistent with the scales of spatial coherence from MODIS data, in both data sets power spectra indicate AOD variability is manifest primarily on synoptic and annual time scales. Conversely, AE variability in MODIS data is primarily focused on seasonal, semiannual, and annual time scales, and there is an additional mode of AE variability at ∼30 days in the AERONET measurements. The frequency of co-occurrence of extreme AOD values (>local 90th percentile) decreases to below 50% at ∼150 km from a central grid cell, but is above that expected by random chance over almost all of eastern North America, indicating supra-regional scale extreme events.

SPARTAN: a global network to evaluate and enhance satellite-based estimates of ground-level particulate matter for global health applications

Abstract. Ground-based observations have insufficient spatial coverage to assess long-term human exposure to fine particulate matter (PM2.5) at the global scale. Satellite remote sensing offers a promising approach to provide information on both short- and long-term exposure to PM2.5 at local-to-global scales, but there are limitations and outstanding questions about the accuracy and precision with which ground-level aerosol mass concentrations can be inferred from satellite remote sensing alone. A key source of uncertainty is the global distribution of the relationship between annual average PM2.5 and discontinuous satellite observations of columnar aerosol optical depth (AOD). We have initiated a global network of ground-level monitoring stations designed to evaluate and enhance satellite remote sensing estimates for application in health-effects research and risk assessment. This Surface PARTiculate mAtter Network (SPARTAN) includes a global federation of ground-level monitors of hourly PM2.5 situated primarily in highly populated regions and collocated with existing ground-based sun photometers that measure AOD. The instruments, a three-wavelength nephelometer and impaction filter sampler for both PM2.5 and PM10, are highly autonomous. Hourly PM2.5 concentrations are inferred from the combination of weighed filters and nephelometer data. Data from existing networks were used to develop and evaluate network sampling characteristics. SPARTAN filters are analyzed for mass, black carbon, water-soluble ions, and metals. These measurements provide, in a variety of regions around the world, the key data required to evaluate and enhance satellite-based PM2.5 estimates used for assessing the health effects of aerosols. Mean PM2.5 concentrations across sites vary by more than 1 order of magnitude. Our initial measurements indicate that the ratio of AOD to ground-level PM2.5 is driven temporally and spatially by the vertical profile in aerosol scattering. Spatially this ratio is also strongly influenced by the mass scattering efficiency.

Inter-Annual Variations of Cloud and Precipitation and their Possible Relationships with Surface Aerosols in Shanghai

ABSTRACTAerosol-cloud-precipitation interactions have attracted much more attention for decades, but there still remain many uncertainties in assessing global climate. Long-term ground-based measurements of aerosol, cloud and precipitation in Shanghai were used to examine their inter-annual variations and possible relationships. During 1990–2010, the yearly-averaged total cloud cover (TCC) and low cloud cover (LCC) decrease on average by 0.58% and 2.49% per year. LCC correlates to surface aerosols (e.g., PM10), with a correlation coefficient (R) of 0.67. Aerosol optical depth (AOD), as an indicator of columnar aerosol loading, shows a non-significant correlation with cloud cover. The yearly-aggregated heavy and extreme rain days and their rainfall amount increase gradually. The moderate rain day enhances but its annual rainfall amount declines year by year, while the light rain exhibits an opposite pattern to the moderate rain. These results imply that local aerosols maybe exert somewhat enforcing on low cloud and light rain through possible entrainment or updraft that can bring up surface particles into free troposphere, whereas its influence to total cloud and precipitation is negligible at a small scale. Future studies are needed to ensure whether local aerosols to directly affect low cloud, and to explore how surface aerosols to enter into higher atmospheric layers and impact cloud and precipitation at larger scales.

Aerosol Column Size Distribution and Water Uptake Observed during a Major Haze Outbreak over Beijing on January 2013

Haze can cause serious atmospheric pollution affecting air quality, human health and even global climate. In order to investigate aerosol columnar size distribution and water uptake during haze evolution, we analyse ground-based observations during an extreme winter pollution case at Beijing on 12 January 2013 (haze day) as compared to those registered on 9 January (non-haze day). We study the evolution of the aerosol size distribution using retrievals from a ground-based CIMEL sun-sky radiometer of the Aerosol Robotic Network (AERONET). Our results show that while the hourly volume growth rate of a sub-micron fine mode presented in the size distribution remains below 0.010 mu m(3)/mu m(2)/hr during the non-haze day, it can rapidly increase during haze pollution event, reaching a maximum value of 0.075 mu m(3)/mu m(2)/hr. The mean size of fine mode particles becomes larger during the pollution event, while it is reduced for coarse mode particles. The mean volume of water uptake is 0.013 mu m(3)/mu m(2) in haze day, being about 13 times larger than that in non-haze day. Meanwhile, the volume of water-soluble inorganic aerosols increases from 0.036 to 0.298 mu m(3)/mu m(2), partly explained by the increase of water uptake during the haze event and also likely by accumulation of particle matters due to stagnating atmospheric conditions. The increase of water-soluble particle volume, which is enhanced by water uptake, significantly contributes to haze evolution.

Accuracy of near‐surface aerosol extinction determined from columnar aerosol optical depth measurements in Reno, NV, USA

AbstractThe aim of the present work is a detailed analysis of aerosol columnar optical depth as a tool to determine near‐surface aerosol extinction in Reno, Nevada, USA, during the summer of 2012. Ground and columnar aerosol optical properties were obtained by use of in situ Photoacoustic and Integrated Nephelometer and Cimel CE‐318 Sun photometer instruments, respectively. Both techniques showed that seasonal weather changes and fire plumes had enormous influence on local aerosol optics. The apparent optical height followed the shape but not magnitude of the development of the convective boundary layer when fire conditions were not present. Back trajectory analysis demonstrated that a local flow known as the Washoe Zephyr circulation often induced aerosol transport from Northern California over the Sierra Nevada Mountains that increased the aerosol optical depth at 500 nm during afternoons when compared with mornings. Aerosol fine mode fraction indicated that afternoon aerosols in June and July and fire plumes in August were dominated by submicron particles, suggesting upwind urban plume biogenically enhanced evolution toward substantial secondary aerosol formation. This fine particle optical depth was inferred to be beyond the surface, thereby complicating use of remote sensing measurements for near‐ground aerosol extinction measurements. It is likely that coarse mode depletes fine mode aerosol near the surface by coagulation and condensation of precursor gases.

Localization of aerosol sources in East-European region by back-trajectory statistics

A concentration-weighted trajectory method for aerosol source localization based on joint statistical analysis of aerosol column volume concentrations and back-trajectory data was used to estimate the spatial distribution of aerosol sources in the East-European region. The aerosol column volume concentration data measured at five AERONET network sites, Belsk, Minsk, Kyiv, Moldova/Kishinev, and Sevastopol, were used. The geographical areas responsible for increased aerosol content at the monitoring sites were mapped separately for coarse-mode and fine-mode aerosol fractions. The investigated area is located between 42° and 62° N in latitude and between 12° and 50° E in longitude.It was shown that the northeastern territories (in relation to the monitoring stations) give a small contribution to the coarse-mode aerosol content. The events of increased coarse-mode aerosol concentration have been caused by sources in the southeastern regions. On average, the air masses with a large content of coarse-mode aerosol particles were delivered to all stations from regions around Donetsk, Rostov-on-Don, and Kharkiv cities. The fine-mode aerosol fraction originated from areas of Tambov, Voronezh, and Kharkiv cities. The calculated aerosol source regions partly correspond to European Monitoring and Evaluation Programme data for eastern Europe. The cause of difference between calculated regions responsible for increased aerosol content at the monitoring sites and the sources of particle emission according to European Monitoring and Evaluation Programme data are discussed.

Optical, size and mass properties of mixed type aerosols in Greece and Romania as observed by synergy of lidar and sunphotometers in combination with model simulations: A case study

A coordinated experimental campaign aiming to study the aerosol optical, size and mass properties was organized in September 2012, in selected sites in Greece and Romania. It was based on the synergy of lidar and sunphotometers. In this paper we focus on a specific campaign period (23–24 September), where mixed type aerosols (Saharan dust, biomass burning and continental) were confined from the Planetary Boundary Layer (PBL) up to 4–4.5km height. Hourly mean linear depolarization and lidar ratio values were measured inside the dust layers, ranging from 13 to 29 and from 44 to 65sr, respectively, depending on their mixing status and the corresponding air mass pathways over Greece and Romania. During this event the columnar Aerosol Optical Depth (AOD) values ranged from 0.13 to 0.26 at 532nm. The Lidar/Radiometer Inversion Code (LIRIC) and the Polarization Lidar Photometer Networking (POLIPHON) codes were used and inter-compared with regards to the retrieved aerosol (fine and coarse spherical/spheroid) mass concentrations, showing that LIRIC generally overestimates the aerosol mass concentrations, in the case of spherical particles. For non-spherical particles the difference in the retrieved mass concentration profiles from these two codes remained smaller than ±20%. POLIPHON retrievals showed that the non-spherical particles reached concentrations of the order of 100–140μg/m3 over Romania compared to 50–75μg/m3 over Greece. Finally, the Dust Regional Atmospheric Model (DREAM) model was used to simulate the dust concentrations over the South-Eastern Europe.

The role of aerosol absorption in driving clear‐sky solar dimming over East Asia

AbstractSurface‐based observations indicate a significant decreasing trend in clear‐sky downward surface solar radiation (SSR) over East Asia since the 1960s. This “dimming” is thought to be driven by the region's long‐term increase in aerosol emissions, but little work has been done to quantify the underlying physical mechanisms or the contribution from aerosol absorption within the atmospheric column. Given the distinct climate impacts that absorption‐driven dimming may produce, this constitutes an important, but thus far rather neglected, line of inquiry. We examine experiments conducted in the Geophysical Fluid Dynamics Laboratory's atmospheric general circulation models, AM2.1 and AM3, in order to analyze the model‐simulated East Asian clear‐sky SSR trends. We also use the models' stand‐alone radiation module to examine the contribution from various aerosol characteristics in the two models (such as burden, mixing state, hygroscopicity, and seasonal distribution) to the trends. Both models produce trends in clear‐sky SSR that are comparable to that observed but via disparate mechanisms. Despite their different aerosol characteristics, the models produce nearly identical increases in aerosol absorption since the 1960s, constituting as much as half of the modeled clear‐sky dimming. This is due to a compensation between the differences in aerosol column burden and mixing state assumed in the two models, i.e., plausible clear‐sky SSR simulations can be achieved via drastically different aerosol parameterizations. Our novel results indicate that trends in aerosol absorption drive a large portion of East Asian clear‐sky solar dimming in the models presented here and for the time periods analyzed and that mechanistic analysis of the factors involved in aerosol absorption is an important diagnostic in evaluating modeled clear‐sky solar dimming trends.

Fire risk, atmospheric chemistry and radiative forcing assessment of wildfires in eastern Mediterranean

The current research study aims at investigating the atmospheric implications of a major fire event in the Mediterranean area. For this purpose, a regional aerosol model coupled online with meteorology (COSMO-ART) is applied over Greece during late summer 2007. Fire risk model results proved to be adequate in reproducing the highly destructive event, which supports further applications for national meteorological forecasts and early warning systems for fire prevention. Columnar aerosol loading field predictions are consistent with satellite maps, which further allows for the correlation of this wildfire event to the atmospheric chemistry and the radiative forcing. Gaseous chemistry resembles that in urban environments and led to nitrogen dioxide and ozone exceedances in several cities in proximity to and downwind the fire spots, respectively. Influence in Athens is found significant from the Euboean plume (45% of total surface PM10) and small (5%) from the fires in Peloponnese. Fire events are indicated by sharp increases in organic to elemental carbon (6), together with sharp decreases in secondary to total organic components (0.1), in comparison to their values during the pre- and post-fire period over Athens (1 and 0.6, respectively). The change in the radiative budget induced by the fire plume is found negative (3-day-average value up to −10 W m−2). Direct heat input is found negligible, thus the net temperature effect is also negative over land (−0.5 K). Nevertheless, positive temperature changes are found overseas (hourly value up to +2 K), due to the amplified radiation absorption by aged soot, coupled to the intense stabilization of the atmosphere above the sea surface.

Aerosol radiometric properties at Western Spain (Cáceres station)

ABSTRACTThis paper analyses the radiometric properties of aerosol column over Western Spain. It is based on 7‐year data series of aerosol parameters at the AERONET Cáceres station (Spain) as measured by CIMEL sun‐photometers. The study period extends along almost 7 years: from July 2005 to June 2012. The paper aims at analysing the temporal evolution, mean values and spectral dependence of some fundamental aerosol parameters such as aerosol optical depth (τ), Ångström parameter (α), single scattering albedo (ω), asymmetry parameter (g) and volume size distribution (dV dlogr−1); and their relationship with the most frequent air masses that arrive at Western Spain. Mean values correspond to aerosols of small size and low concentration (mean τ500 = 0.11; mean α = 1.38). In fact, 50% of days correspond to ‘continental‐clean’ type. However, there is a certain variability of conditions, with more than 25% of medium and high turbidity cases with τ500 higher than 0.20. These episodes of high turbidity occur more frequently in August and September and are usually due to the influence of desert‐dust aerosol, biomass burning, continental aerosol, or a mixture of them. The analysis of the all basic and derived aerosol parameters is explained by the main influences: continental location, exposed to maritime aerosols coming from the Atlantic Ocean, and affected by Saharan dust intrusions.

Study on Aerosol Model and Sources at Zhoushan, China Using Sun-sky Photometer Observation

Aerosol models are widely used in satellite remote sensing to derived aerosol mode from aerosol optical and microphysical properties. One year of ground-based aerosol remote sensing observations were carried out using sun-sky radiometer measurements in Zhoushan (122.1897E, 29.9944N), Zhejiang Province, Eastern China. At the same time column Aerosol Optical Depth (AOD), Ångström exponent (AE), Single Scattering Albedo (SSA), asymmetry factor (g), complex refractive index and column aerosol volume spectral distribution were retrieved by mature code as well as some procedures, such as radiometer calibration, cloud screening and data selection strategies. Aerosol size parameters were separated as fine effective radius (rvf) and coarse effective radius (rvc) due to the column aerosol size distribution is generally bimodal lognormal distribution. The relationship between these parameters and effective radius was shown and analyzed. It is shown that aerosol in Zhoushan is urban-industrial type dominate, mixed with marine aerosol and mineral dust aerosol. As a result, this study showed a part of aerosol comes from mainland industrial areas by using the backward trajectory model.

Assessment of OMI near‐UV aerosol optical depth over land

AbstractThis is the first comprehensive assessment of the aerosol optical depth (AOD) product retrieved from the near‐UV observations by the Ozone Monitoring Instrument (OMI) onboard the Aura satellite. The OMI‐retrieved AOD by the UV aerosol algorithm (OMAERUV version 1.4.2) was evaluated using collocated Aerosol Robotic Network (AERONET) level 2.0 direct Sun AOD measurements over 8 years (2005–2012). A time series analysis of collocated satellite and ground‐based AOD observations over 8 years shows no discernible drift in OMI's calibration. A rigorous validation analysis over 4 years (2005–2008) was carried out at 44 globally distributed AERONET land sites. The chosen locations are representative of major aerosol types such as smoke from biomass burning or wildfires, desert mineral dust, and urban/industrial pollutants. Correlation coefficient (ρ) values of 0.75 or better were obtained at 50% of the sites with about 33% of the sites in the analysis reporting regression line slope values larger than 0.70 but always less than unity. The combined AERONET‐OMAERUV analysis of the 44 sites yielded a ρ of 0.81, slope of 0.79, y intercept of 0.10, and 65% OMAERUV AOD falling within the expected uncertainty range (largest of 30% or 0.1) at 440 nm. The most accurate OMAERUV retrievals are reported over northern Africa locations where the predominant aerosol type is desert dust and cloud presence is less frequent. Reliable retrievals were documented at many sites characterized by urban‐type aerosols with low to moderate AOD values, concentrated in the boundary layer. These results confirm that the near‐UV observations are sensitive to the entire aerosol column. A simultaneous comparison of OMAERUV, Moderate Resolution Imaging Spectroradiometer (MODIS) Deep Blue, and Multiangle Imaging Spectroradiometer (MISR) AOD retrievals to AERONET measurements was also carried out to evaluate the OMAERUV accuracy in relation to those of the standard aerosol satellite products. The outcome of the comparison indicates that OMAERUV, MODIS Deep Blue, and MISR retrieval accuracies in arid and semiarid environments are statistically comparable.

Lidar profiling of aerosol scavenging parameters at a tropical station, Pune, India

In this study, we deal with observations of aerosol column content (height integration of vertical distribution of aerosol number density) that have been carried out using an Ar+ lidar for three different measurement cycles (each cycle consisting of three experimental days associated with non-rain, rain, and non-rain, respectively) of weekly spaced observations for pre-monsoon (March/April 1994), monsoon (September 1991), and post-monsoon (October 1998). Based on these observed profiles of aerosol number concentration on rainy days with respect to those on non-rainy days, vertical distributions of scavenging collection efficiencies (SCEs) are computed and discussed in this article. The SCE is found to decrease from 0.3 to 0.01 between the heights, 100 and 800 m for thunderstorm rain in April 1994, and during monsoon, it increases from 0.1 to 0.7. In the October 1998 episode, SCE was found to increase initially from 0.35 to 0.75 for heights between 40 and 200 m and thereafter decrease to 0.35 in the height interval of 200–800 m. For the rainfall intensity increase from 1 to 10 mm hour−1, the corresponding scavenging coefficient (SC) for atmospheric layer 50–100 m varies from 4 × 10−6 to 4 × 10−5 s−1 for thunderstorm in April 1994 and between 5 × 10−6 and 5 × 10−5 s−1 in October 1998, respectively. During monsoon, these values vary from 3 × 10−5 to 5 × 10−4 s−1. They lie in the range of those observed in the earlier field studies. The results are found useful to establish links between aerosols and cloud properties, and the influence of such interactions on weather and climate.