Fine Mode Research Articles

Retrieval of total and fine mode aerosol optical depth by an improved MODIS Dark Target algorithm.

Total and fine mode aerosol optical depth (AODT and AODF), as well as the fine mode fraction (FMF=AODF/AODT), are critical variables for climate change and atmospheric environment studies. The retrievals with high accuracy from satellite observations, particularly FMF and AODF over land, remain challenging. This study aims to improve the Moderate-resolution Imaging Spectro-radiometer (MODIS) land dark target (DT) algorithm for retrieving AODT, AODF, and FMF on a global scale. Based on the fact that the underestimated surface reflectance (SR) could overestimate the AODT and underestimate the aerosol size parameter in the DT algorithm, two robust schemes were developed to improve SR determination: the first (NEW1 DT) used the top of the atmosphere reflectance instead of SR at 2.12µm; the second (NEW2 DT) used eleven-year MODIS data to establish a monthly spectral SR relationship model (2.12-0.47 and 2.12-0.65µm) database at pixel-by-pixel scale. Then a novel lookup table approach based on the physical process was proposed to retrieve the AODF and FMF. The new MODIS AODT, FMF, and AODF were compared to AERosol RObotic NETwork (AERONET) retrievals. Results showed that the root mean square error (RMSE) was 0.096-0.103, 0.098-0.099, and 0.167-0.180 for the new AODTs, AODFs, and FMFs, respectively, which were better than that of the Collection 6.1 (C6.1) DT (0.117, 0.235, and 0.426) in the validation by global AERONET sites. From the validation results, NEW2 DT provided better AODT and coarse mode AOD retrievals, while NEW1 DT had better AODF and FMF performances. The spatial patterns of AODF, FMF, and AODC of the new DT algorithms were comparable to those of the Polarization and Directionality of the Earth's Reflectances aerosol product. Hence, the new algorithms have the potential to provide global AODT, FMF, and AODF products over land to the scientific community with high accuracy using long-term MODIS data.

Retrieval of Aged Biomass-Burning Aerosol Properties by Using GRASP Code in Synergy with Polarized Micro-Pulse Lidar and Sun/Sky Photometer

The aim of this study was to analyze the potential of the GRASP code to retrieve optical and microphysical properties vertically-resolved using a synergy of polarized Micro-Pulse Lidar and Sun/sky photometer observations. The focus was on the long-range transport of Canadian aged-smoke plumes observed at El Arenosillo/Huelva (Spain) from 7 to 8 September 2017. Both the columnar and height-resolved microphysical and optical properties were assessed in comparison with AERONET data and vertical lidar-retrieved profiles, respectively. In particular, the vertical properties were also derived using the POLIPHON approach, which serves as a comparison for GRASP retrievals. The retrieved columnar aerosol microphysical properties (volume concentration and effective radius) showed an excellent agreement, with negligible differences, and were within the uncertainties. Nevertheless, for the retrieved columnar optical properties, we could only perform an individual comparison, due to the strong AERONET limitations, and although the agreements were generally good, no conclusions were obtained, due to differences in the real refractive index and due to the large uncertainties obtained in the retrievals. For the vertical profiles, however, we present a large advance that permits obtaining aerosol backscatter and extinction coefficients, plus volume concentrations, without the need for internal assumptions (extinction-to-backscatter ratios and depolarization measurements), due to the very good agreement observed between GRASP and the lidar-derived methodologies. However, the separation of the properties into their fine and coarse modes was not feasible using the one-wavelength elastic lidar measurements with the GRASP retrieval configuration used in this work. Therefore, current studies are being addressed to assessing the introduction of lidar depolarization in the GRASP code as an encouraged added-value, for the improvement of the retrieval of vertical aerosol properties.

Parameterization of below-cloud scavenging for polydisperse fine mode aerosols as a function of rain intensity

The below-cloud aerosol scavenging process by precipitation is one of the most important mechanisms to remove aerosols from the atmosphere. Due to its complexity and dependence on both aerosol and raindrop sizes, wet scavenging process has been poorly treated, especially during the removal of fine particles. This makes the numerical simulation of below-cloud scavenging in large-scale aerosol models unrealistic. To consider the slip effects of submicron particles, a simplified expression for the diffusion scavenging was developed by approximating the Cunningham slip correction factor. The derived analytic solution was parameterized as a simple power function of rain intensity under the assumption of the lognormal size distribution of particles. The resultant approximated expression was compared to the observed data and the results of previous studies including a 3D atmospheric chemical transport model simulation. Compared with the default GEOS-Chem coefficient of 0.00106R0.61 and the observation-based coefficient of 0.0144R0.9268, the coefficient of a and b in Λm = aRb spread in the range of 0.0002- 0.1959 for a and 0.3261- 0.525 for b over a size distribution of GSD of 1.3–2.5 and a geometric mean diameter of 0.01- 2.5 µm. Overall, this study showed that the scavenging coefficient varies widely by orders of magnitude according to the size distribution of particles and rain intensity. This study also demonstrated that the obtained simplified expression could consider the theoretical approach of aerosol polydispersity. Our proposed analytic approach showed that results can be effectively applied for reduced computational burden in atmospheric modeling.

Columnar aerosol optical depth, water vapor and ozone over a semi-arid urban location of western India: Potential sources and direct radiative effects

Continuous measurements of Aerosol Optical Depth (AOD), columnar water vapor (WV) and Ozone (O3) concentrations were made over a semi-arid urban location Rajkot (22.29°N, 70.74°E, and 142 m AMSL) in the western India. The annual mean values of AOD, WV and O3 were 0.37 ± 0.15, 1.44 ± 0.6 gm cm−2 and 243 ± 18 DU during 2016–2019. AOD showed large seasonal variability mostly dominated by abundant coarse mode aerosols (Angstrom Exponent, AE < 0.65 and AOD ∼ 0.37) during pre-monsoon and monsoon, mainly caused by wind-blown and transported dust from nearby Thar and Kutch desert. Mixture of fine and coarse mode aerosols were abundant (AE = 1.13 ± 0.26) during post-monsoon influenced by both anthropogenic and natural sources. Columnar WV were also higher in pre-monsoon and monsoon seasons. The O3 concentrations is higher during pre-monsoon (247 DU) and lower during monsoon (230 DU). The vertical distribution of aerosol extinction coefficient derived from satellite (CALIPSO) based observations revealed the dominance of dust aerosols (∼74 %) in pre-monsoon; smoke and polluted dust in winter and post monsoon period. The trajectory clusters and concentration weighted trajectory maps also indicated the combined effect of anthropogenic (especially from the northern part of India) and natural aerosol sources during the post-monsoon period. Associated with the higher anthropogenic components during post-monsoon season, aerosol direct radiative forcing depicted surface dimming as high as − 48.7 ± 12.6 Wm−2, resulting in atmospheric forcing of 42.6 ± 12.5 Wm−2.

Understanding Sources and Drivers of Size-Resolved Aerosol in the High Arctic Islands of Svalbard Using a Receptor Model Coupled with Machine Learning.

Atmospheric aerosols are important drivers of Arctic climate change through aerosol–cloud–climate interactions. However, large uncertainties remain on the sources and processes controlling particle numbers in both fine and coarse modes. Here, we applied a receptor model and an explainable machine learning technique to understand the sources and drivers of particle numbers from 10 nm to 20 μm in Svalbard. Nucleation, biogenic, secondary, anthropogenic, mineral dust, sea salt and blowing snow aerosols and their major environmental drivers were identified. Our results show that the monthly variations in particles are highly size/source dependent and regulated by meteorology. Secondary and nucleation aerosols are the largest contributors to potential cloud condensation nuclei (CCN, particle number with a diameter larger than 40 nm as a proxy) in the Arctic. Nonlinear responses to temperature were found for biogenic, local dust particles and potential CCN, highlighting the importance of melting sea ice and snow. These results indicate that the aerosol factors will respond to rapid Arctic warming differently and in a nonlinear fashion.

Aerosol Optical Characteristics with Ground-based Measurements via Sun Photometer and Its Relationship with PM Particle Concentration in Chang'an

The simultaneous quantitative investigation of aerosol ground observation data and particle concentration data is important for a better understanding of the vertical distribution characteristics of air pollution and formulating reasonable air pollution control measures in Chang'an, Xi'an. CE-318 measurements from October 2018 to April 2021 were systematically analyzed to reveal the seasonal and yearly variations in atmospheric aerosols in Chang'an. Then, the relationship between AOD and particle concentration in different seasons and different pollution degrees was explored. The obtained results were as follows:① the seasonal variation in AOD in Chang'an was determined, whereby autumn (1.02)>winter (1.00)>summer (0.63)>spring (0.47). Distinct monthly and inter-annual differences in AOD were observed, showing that the annual average of AOD in 2019 was higher than that in 2020. ② Obvious seasonal and monthly differences in aerosol main control modes were observed; the dominant mode of aerosols gradually changed from coarse mode to fine mode from spring to winter. The seasonal variation in the main control mode of aerosols in 2019 was similar to that in the whole observation period. The seasonal aerosol Angstrom wavelength index (Angstrom) was evenly distributed in 2020, and aerosol particles existed in coarse mode form. Generally speaking, the aerosol type in Chang'an was mostly mixed aerosol throughout the whole observation period. ③ Significant seasonal variations in the relationship between AOD and Angstrom was shown, in which the air pollution in spring was dominated by coarse mode aerosol particles. The local pollution in summer was caused by coarse and fine mode aerosol particles, and the fine mode particles were dominant when the pollution was obvious. The characteristic distribution of Angstrom in autumn and winter was similar; in case of local pollution, the coarse mode aerosol particles were dominant, and in case of obvious pollution, the fine mode aerosol particles were dominant. ④ The monthly concentration variation trend of PM2.5 and PM10 in Chang'an consistent with the maximum and minimum values appeared in January and summer, respectively. Seasonal variation in the concentration of PM2.5 and PM10 was apparent, with the highest values in winter. ⑤ A positive correlation between AOD and particulate matter concentration in different seasons and pollution levels was obtained during the observation periods, but the correlation coefficient differed. The specific characteristics were as follows:the correlation between AOD and PM2.5 concentration was greater than that with PM10 concentration; the correlation between AOD and particle concentration in autumn and winter was greater than that in spring and summer; and the correlation between AOD and particulate matter concentration was greater in polluted weather. Particle concentration was the most important determinant of AOD change, followed by relative humidity, which was the meteorological factor with the highest interpretation rate of AOD change in Chang'an. This indicates that a higher correlation between AOD and particle concentration would benefit from a reasonable humidity correction of AOD.

Complex Interplay Between Organic and Secondary Inorganic Aerosols With Ambient Relative Humidity Implicates the Aerosol Liquid Water Content Over India During Wintertime

AbstractAerosol Liquid Water Content (ALWC), a ubiquitous component of atmospheric aerosols, modulates atmospheric chemistry through aerosol surface reactions and reduces the atmospheric visibility. However, the complex dependency of ALWC on aerosol chemistry and relative humidity (RH) in the Indian region remains poorly characterized. Here, we combine available measurements of aerosol chemical composition with thermodynamic model, ISORROPIA2.1, to reveal a comprehensive picture of ALWC in fine mode aerosols during the winter season over the Indian continental region. The factors modulating ALWC are primarily dependent on the RH, such that the effect of aerosol dry mass and hygroscopicity are significant at high RH while the effect of hygroscopicity significantly reduces with decreasing RH. ALWC is observed to display a sharp non‐linear rise, beyond a critical value of ambient RH dependent on the particle hygroscopicity. Further analysis by coupling Weather Research Forecasting‐Chem simulation with ISORROPIA2.1 revealed significant spatial heterogeneity in ALWC over India, strongly associating with regions of high aerosol mass loading and RH. The Indo‐Gangetic Plain is consequently observed to be a hotspot of higher ALWC, which explains the prevalent conditions of haze and smog during winter in this region. Our findings re‐emphasize that high aerosol mass resulting from intense pollution is vital in modulating aerosol–climate interaction under favorable meteorological conditions. Observations suggest the need for localized pollution control strategies, directed at the reduction in aerosol emissions of specific chemical composition observed to contribute to the enhancement in PM through an increase in ALWC during wintertime in the region.

A Coupled Evaluation of Operational MODIS and Model Aerosol Products for Maritime Environments Using Sun Photometry: Evaluation of the Fine and Coarse Mode

Although satellite retrievals and data assimilation have progressed to where there is a good skill for monitoring maritime Aerosol Optical Depth (AOD), there remains uncertainty in achieving further degrees of freedom, such as distinguishing fine and coarse mode dominated species in maritime environments (e.g., coarse mode sea salt and dust versus fine mode terrestrial anthropogenic emissions, biomass burning, and maritime secondary production). For the years 2016 through 2019, we performed an analysis of 550 nm total AOD550, fine mode AOD (FAOD550; also known as FM AOD in the literature), coarse mode AOD (CAOD550), and fine mode fraction (η550) between Moderate Resolution Spectral Imaging Radiometer (MODIS) V6.1 MOD/MYD04 dark target aerosol retrievals and the International Cooperative for Aerosol Prediction (ICAP) core four multi-model consensus (C4C) of analyses/short term forecasts that assimilate total MODIS AOD550. Differences were adjudicated by the global shipboard Maritime Aerosol Network (MAN) and selected island AERONET sun photometer observations with the application of the spectral deconvolution algorithm (SDA). Through a series of conditional and regional analyses, we found divergence included regions of terrestrial influence and latitudinal dependencies in the remote oceans. Notably, MODIS and the C4C and its members, while having good correlations overall, have a persistent +0.04 to +0.02 biases relative to MAN and AERONET for typical AOD550 values (84th% &lt; 0.28), with the C4C underestimating significant events thereafter. Second, high biases in AOD550 are largely associated with the attribution of the fine mode in satellites and models alike. Thus, both MODIS and C4C members are systematically overestimating AOD550 and FAOD550 but perform better in characterizing the CAOD550. Third, for MODIS, findings are consistent with previous reports of a high bias in the retrieved Ångström Exponent, and we diagnosed both the optical model and cloud masking as likely causal factors for the AOD550 and FAOD550 high bias, whereas for the C4C, it is likely from secondary overproduction and perhaps numerical diffusion. Fourth, while there is no wind-speed-dependent bias for surface winds &lt;12 m s−1, the C4C and MODIS AOD550s also overestimate CAOD550 and FAOD550, respectively, for wind speeds above 12 m/s. Finally, sampling bias inherent in MAN, as well as other circumstantial evidence, suggests biases in MODIS are likely even larger than what was diagnosed here. We conclude with a discussion on how MODIS and the C4C products have their own strengths and challenges for a given climate application and discuss needed research.

The Potential for Great Barrier Reef Regional Climate Regulation via Dimethylsulfide Atmospheric Oxidation Products

Research related to the potential for coral reef-derived dimethylsulfide (DMS) oxidation products to regulate the regional climate of the Great Barrier Reef (GBR) according to the CLAW hypothesis is summarized in this mini review. The GBR has been indicated as a region of high DMS production where atmospheric emissions may be increased when corals are subject to environmental stresses associated with low tide. During low wind speeds over aerially exposed coral reefs, plumes of atmospheric DMS and new sulfate-containing nano-particle production under photo-oxidative conditions have been detected on the GBR. Hygroscopic growth of these particles in combination with coagulation and condensation processes could potentially provide a coral-mediated mechanism of new aerosol for seeding low-level stratocumulus clouds. Fine mode aerosol optical depth over GBR coral reefs has been correlated with low wind speeds and a coral stress metric formulated as a function of irradiance, water clarity, and tide height. This correlation has been proposed as a possible mechanism by which the GBR might alter the optical properties of the overlying atmosphere to attenuate local insolation leading to regional climate regulation. However, recent regional-scale aerosol-climate modeling indicates that the potential for GBR regional climate regulationviaDMS atmospheric oxidation products is weak under current anthropogenic conditions which have instigated mass coral bleaching events along the entire length of the GBR between 1998 and 2022. This increased bleaching indicates that DMS oxidation products are insufficient to regulate the regional climate of the GBR according to the CLAW hypothesis under current global warming conditions.

Impacts of the Variations of Aerosols Components and Relative Humidity on the Visibility and Particles Size Distribution of the Desert Atmosphere: Validating Results Obtained from OPAC 4.0 using MERRA-2 Model (Angstrom Exponent and Extinction Coefficient) Data

In this work, data extracted from OPAC 4.0 was compared and validated with 11 years data record from MEERA-2 model (average Angstrom Exponent and average Extinction Coefficient). The 11 years MEERA-2 model data for 10 selected deserts was extracted at an average relative humidity (RH) condition of 78%RH while OPAC considers eight different (RH) levels (00% to 99%RH). Based on the investigation, MEERA-2 model has the highest angstrom exponent (a) values for (Arabian, Danakil, Ferlo, Lompoul, Patagonian, Registan and Syrian deserts), which is greater than 1, and this signifies the dominance of fine mode particles over coarse mode particles when compared to OPAC 4.0. It can be seen that Chalbi (0.845), Karoo (0.482) and Sahara (0.417) deserts have an a values which is less than 1(indicating the dominance of coarse mode particles over fine mode particles). It can also be said that, MEERA-2 (a) is still greater than that of OPAC and this shows that the deserts atmosphere can be dominated by fine mode particles. The angstrom exponent (a) for OPAC 4.0 fluctuate all through the four studied components except for WASO which increases with the increase in RH and particles concentration (and this signifies that the particles dissolved as they uptake water and reach their saturation level). Based on the results of the investigation (time series analysis), it was found that the model’s significance (b) level are very high, and this shows that the aerosols distribution fluctuates around a reasonable stable, which signifies that the models are very significant. The analysis further found that, the significance (d) from the seasonal aspect is very poor except for Ferlo and Lompoul deserts, this signifies that season effect is consistent over time. It was also found that, the MEERA-2 has the highest visibility (km) over (OPAC 4.0). The investigation further revealed that the Arabian, Syrian and Patagonian deserts have the highest visibility (km) in the months of January, February, June, November and December. OPAC model underestimated the visibility when compared to MEERA-2 model.

Long-term variations and comparison of aerosol optical properties based on MODIS and ground-based data in Thailand

Comparison and analysis of Moderate Resolution Imaging Spectroradiometer (MODIS), Aerosol Robotic Network (AERONET), and SKYNET aerosol optical depth (AOD) products were investigated at four AERONET and two SKYNET stations in Thailand from 2006 to 2020. AERONET Level 2.0 and MODIS Deep Blue (DB) Collection 6.1 data were applied. Aqua and Terra MODIS AODs (satellite AODs) were compared to AERONET and SKYNET AODs (ground based AODs). Ground-based and satellite AODs were in good agreement, giving a high correlation (R2 = 0.75) in Ubon Ratchathani, associated with biomass burning. The long-term trend in AOD was analyzed. Both satellite and ground based AODs demonstrate increasing trends in AOD over Thailand associated with the urbanized area and traffic congestion. Aerosol particles are categorized into dust, sea salt, and biomass burning, containing fine and coarse modes. A variation between satellite data measurements depended on surface reflectances, such as the large water body surrounding (Songkhla) and the impact of surface albedo (Chiang Mai). Higher AOD values were observed between February to April. In addition, meteorological parameters are directly related to aerosol concentrations, while no significant connection could be developed in the observed values between Angstrom exponent (AE) and Meteorological parameters. Meteorological parameters and temperature inversion more influenced AOD concentrations in February. Nevertheless, the hypothesis showed 95% confidence interval of AODs retrieved from satellite data fell within the confidence range. Therefore, satellite aerosol products are sufficiently accurate for estimating aerosol climatology.

A year-long study on PM2.5 and its carbonaceous components over eastern Himalaya in India: Contributions of local and transported fossil fuel and biomass burning during premonsoon

A year-long (March 2019–February 2020) study on the characterization of fine mode carbonaceous aerosols has been conducted over a high altitude urban atmosphere, Darjeeling (27.01°N, 88.15°E, 2200 m asl) in eastern Himalaya. The fine mode aerosol (PM2.5; 41.7 ± 23.7 μgm−3), total carbonaceous aerosols (TCA; 19.8 ± 7.7 μgm−3), organic carbon (OC; 8.0 ± 3.9 μgm−3) and elemental carbon (EC; 2.0 ± 0.9 μgm−3) exhibited similar seasonal variability with the highest abundance during winter followed by premonsoon, postmonsoon and minimum in monsoon. The OC:EC varied over a range of 2.8–19.4 whereas the secondary organic carbon ranged between 1.9 and 17.1 μgm−3 respectively. Higher PM2.5 associated with higher winds and elevated mixing layer depth suggest a strong influence of regional and long-range transport. In addition to the usual morning and evening rush-hour peaks, the impact of low land plain regions driven by up-slope valley winds was observed for the carbonaceous components. A novel approach has been taken to find out the individual contributions from the local and transported fossil fuel, biomass burning, and biogenic sources to OC and EC during premonsoon. We observed that the local fossil fuel (43%) contributions dominated over the biomass burning (39%) for EC whereas the contributions of local biomass burning and the local fossil fuel were same (46%) for OC. EC exhibited a higher contribution (18%) from the regional/long-range transport compared to OC (8%). IGP and Nepal were found to be the maximum contributing long distant source regions for the carbonaceous aerosol loading over eastern Himalaya. Such individual source apportionment of carbonaceous aerosols over eastern Himalaya makes the study unique and first-ever of its kind and immensely helpful for building robust mitigation action plans.

Aerosol Distributions and Sahara Dust Transport in Southern Morocco, from Ground-Based and Satellite Observations

The present study investigates aerosols distributions and a strong Sahara dust-storm event that occurred by early August 2018, in the South of Morocco. We used columnar aerosol optical depth (AOD), Angstrom Exponent (AE) and volume size distributions (VSD) as derived from ground-based observations by 2 AERONET (AErosol RObotic NETwork) sun-photometers at Saada (31.63°N, 8.16°W) and Ouarzazate (30.93°N, 6.91°W) sites, over the periods 2004–2019 and 2012–2015, respectively. The monthly seasonal distributions of AOD, AE, and VSD showed a seasonal trend dominated by the annual cycle, with a maximum aerosol load during summer (July–August) and a minimum in winter (December–January), characterized by a coarse mode near the radius of 2.59 μm and a fine mode at the radius of 0.16 μm, respectively. Indeed, this study showed that aerosol populations in southern Morocco are dominated by Saharan desert dust, especially during the summer season. The latter can sometimes be subject of dust-storm events. The case study presented in this paper reports on one of these events, which happened in early August 2018. The HYSPLIT (HYbrid Single Particle Lagrangian Integrated Trajectory) model was used to simulate air-mass back-trajectories during the event. In agreement with ground-based (AERONET sun-photometers) and satellite (CALIOP, MODIS and AIRS) observations, HYSPLIT back-trajectories showed that the dust air-mass at the 4-km layer, the average height of the dust plume, has crossed southern Morocco over the Saada site, with a westward direction towards the Atlantic Ocean, before it changed northward up to the Portuguese coasts.

Biological and Nonbiological Sources of Fluorescent Aerosol Particles in the Urban Atmosphere.

Online detection of bioaerosols based on the light-induced fluorescence (LIF) technique is still challenging due to the complexity of bioaerosols and the external/internal mixing with nonbiological fluorescent compositions. Although many lab studies have measured the fluorescence properties of the biological and nonbiological materials, there is still a scarcity of knowledge of the sources of fluorescent aerosol particles (FAP) in the ambient atmosphere. Here, we fill this gap by combining the online measurement of an LIF-based instrument (wideband integrated bioaerosol sensor, WIBS, 0.8-20 μm) with the measurements of typical biological matter and the compositions related to major nonbiological FAP from May to July in the megacity Beijing. We find that fungal spores and pollen are widely observed in all types of FAP using a WIBS. Bacteria are suggested to be associated with the fine mode FAP (excitation/emission: 280 nm/310-400 nm; 0.8-3 μm). The FL-B and -BC particles (emission in 420-650 nm) contributing the most to FAP are strongly associated with humic-like substances, dust, burning and combustion emissions, and secondary organic aerosols (SOA). This study provides a guide for interpreting individual FAP measured by LIF instruments and points to the applicability of online LIF instruments to characterize nonbiological compositions including SOA.

Application Value and Development Path of Fine Management Mode in Construction Engineering Management

Application Value and Development Path of Fine Management Mode in Construction Engineering Management

The Effect of Varying Aerosol Concentrations on Visibility and Particle Size Distribution in Urban Atmosphere: Validating OPAC Results using MERRA Satellite Aerosol Data

Well validated simulation software and models are meant to add value through a more precise representation of different atmospheric features and climate characteristics that are physically out of reach. In this work, comparison and validation was carried out using the Modern Era Retrospective Analysis for Research and Applications (MERRA) averaged Angstrom Exponents (α) and averaged visibilities for ten urban countries against simulated Optical Properties of Aerosols and Clouds (OPAC) urban components. The simulations of OPAC were performed at 0%, 50%, 70%, 80%, 90%, 95%, 98% and 99% relative humidities (RH) while the MERRA satellite data were extracted at an average of 78% relative humidity. results based on α values showed that OPAC was only able to simulate well the insoluble and soot aerosol particle size distributions of India’s urban atmosphere such that it had approximately the same insoluble and soot aerosol particle size distributions as India. For the rest of the nine countries (USA, Brazil, Indonesia, China, Japan, Mexico, Nigeria, Pakistan and Ethiopia), OPAC was seen to either overestimate or underestimate water soluble, insoluble and soot aerosol particle size distributions. For visibility and water soluble or insoluble aerosol concentrations, OPAC showed good simulated values that were approximately the same as those found within Ethiopia’s and Japan’s urban atmosphere. OPAC also had visibility value and insoluble aerosol concentration that were approximately the same as those found within China’s atmosphere. For all other countries (India, USA, Brazil, Indonesia, Mexico, Nigeria and Pakistan) OPAC either overestimated their visibilities and underestimated their water soluble, insoluble and soot aerosol concentrations or vice versa. With both OPAC and MERRA, the presence of fine mode aerosol particles in an urban atmosphere was established with α values &gt; 1. But MERRA also showed otherwise for three countries (Nigeria, Ethiopia and Pakistan) that had α values &lt; 1 which implied the presence of coarse mode aerosol particles. The relationship between visibility and α satisfied the direct power law for OPAC, for MERRA the relationship approximately satisfied the power law for most of the countries.

An efficient built‐in error detection methodology with fast page‐oriented data comparison in 3D NAND flash memories

This letter presents an efficient built-in error detection methodology for 3D NAND flash memories, in which fast page-oriented data comparison and column parallel error detection are firstly proposed. The methodology takes advantage of the characteristics of page buffer to perform fast page-oriented comparison between test data and reference data. Thanks to that, both fine error detection mode and column parallel error detection mode can be supported for different test scenarios. Analytical results show that it costs about 164.14 μs and 460 ns in fine and column parallel mode respectively to detect a page which is 16 K bytes. Compared with previous work, the error detection time of the proposed column parallel mode is reduced 99.7% for 3D NAND flash memories.

Spatial and seasonal variations of primary and secondary organic aerosols at urban areas and continental background site of China: Ambient levels, size distribution, and sources

Organic aerosols are important constituents of particulate matter (PM) in the atmosphere, however, the studies on their size distribution, particularly for special primary and secondary organic aerosols (POA, SOA), are relatively limited. In this work, the size-segregated PM was collected from five megacities (Shanghai, Guangzhou, Xi’an, Chengdu, Urumqi) and a continental background site (Qinghai Lake, Tibetan Plateau) of China during 2012–2014. Special POA (plant wax n-alkanes, fossil fuel n-alkanes, PAHs, levoglucosan, and trehalose) and biogenic SOA (BSOA, i.e. isoprene oxidants, monoterpene oxidants, and β-caryophyllenic acid) in PM were measured using gas chromatography/mass spectrometry. n-Alkanes were highest in autumn in the Southeast of China and highest in summer in the Northwest of China during the four seasons. PAHs and levoglucosan were higher in the cold season, mainly influenced by residential heating. Isoprene and monoterpene oxidants were higher in the warm season, while β-caryophyllenic acid was found to be much higher in cold seasons. n-Alkanes showed a monomodal distribution, with a peak at the fine mode (<1.1 µm). PAHs and levoglucosan were characterized by an accumulation mode, revealing the peak at <1.1 µm. However, only trehalosedisplayed coarse mode at the six sites, peaking at a size of 3.3–9.0 µm, because it was mostly derived frombiota in desert regions. Isoprene oxidants including 2-methylglyceric acid, 2-methyltetrols, and C5-alkene triols exhibited a unimodal size distribution pattern with a peak in the fine mode. Monoterpene oxidants such as cis-pinic acid, pinonic acid, 3-hydroxyglutaric acid, and 3-methyl-1,2,3-butanetricarboxylic acid exhibited a bimodal size distribution pattern in the whole sampling time, peaking at the size range of <1.1 µm and 3.3–9.0 µm, respectively. Only β-caryophyllenic acid displayed a fine mode at the six sites during the whole sampling time. These findings can be used to support research into the origin and formation mechanisms of POA and BSOA.

Characterization of particulate matter in the iron ore mining region of Itabira, Minas Gerais, Brazil

tabira has in its territory the largest complex of opencast mining in the world, located close to residential areas of the city. The air quality monitoring network installed in the city is the main source of particulate matter (PM) emission data. However, these air quality stations only cover the areas near the mines and do not measure fine particulate matter (PM2.5). Thus, a first field campaign was carried out to characterize PM in the city and to compare high volume data from air quality stations with the dichotomous air sampler data. Results of trajectories’ cluster analysis showed a long-range transport of aerosols during the sampling days from northeast (84% of the trajectories), east-southeast (12%), and south-southwest (3%) directions. Regarding the meteorological conditions during the sampling days, negative correlations were seen between coarse particulate matter (PM10) from mostly air quality stations and all meteorological parameters (but temperature). Results of the X-ray fluorescence and principal component analyses showed that the main trace elements in the coarse (PM2.5-10) and fine modes (PM2.5) are iron and sulfur, associated with emissions from mining activities, air mass transport from regional iron and steelmaking industry activities, vehicle emissions, local and regional biomass burning, and natural biogenic emissions. This work is the first assessment of source apportionment done in the city. Comparisons with other studies, for some large metropolitan areas, showed that Itabira has comparable contributions of sulfur, iron and elements such as copper, selenium, chromium, nickel, vanadium and lead.

Atmospheric aerosols properties over Indo-Gangetic Plain: A trend analysis using ground – Truth AERONET data for the year 2009–2017

The aerosols play an important role in the modification of the regional radiation budget. Long-term trend analysis of properties of atmospheric aerosols is important for policymakers and also for the study of the climatic implications. The Aerosol Robotic Network (AERONET) provides continuous ground-truth aerosol data during cloud-free days since two decades in India. Long-term atmospheric aerosol properties have been studied over four different sites of Indo-Gangetic Plain (IGP): Gandhi College rural background, Kanpur, urban and highly industrial area, Jaipur urban and desert dust influenced region, and Lahore urban and agriculture rich region respectively using AERONET data. The yearly variation of aerosol optical depth (AOD) along with angstrom exponent (AE), single scattering albedo (SSA), size distribution parameters (volume concentration and effective radius), and aerosol radiative forcing (ARF) have been analyzed for nine years from 2009 to 2017. A positive trend of AOD over Kanpur (0.0074/year), a negative trend over Lahore (−0.0054/year), Jaipur – 0.0027/year) and Gandhi college (−0.0008/year) was found. Volume concentration shows the increasing trend of fine mode particles which may be due to increased anthropogenic activities in comparison to natural aerosols over Kanpur, Lahore, Gandhi College, and Jaipur respectively. SSA values over Kanpur and Jaipur show dominancy of scattering while absorbing nature of particles over Lahore and Gandhi College were found. The trend of total atmospheric radiative forcing (ARF ATM ) over Kanpur and Jaipur locations was found to be decreased slightly but not so significantly while over Lahore and Gandhi College trend was found to increase in a significant way. The yearly trend of ARF ATM over Kanpur, Lahore, Jaipur, and Gandhi College was found to be −0.76 Wm −2 /year, 2.22 Wm −2 /year, −0.08 Wm −2 /year, and 3.09 Wm −2 /year respectively.