Elevated Smoke Research Articles

Characterization of aerosol composition: Insights from SEM-EDX analysis and CALIPSO overpasses

The effect of atmospheric aerosols on the earth’s radiation budget is primarily through their direct effects. Understanding aerosols’ morphology and elemental composition is crucial in this context. For two years, from January 2017 to December 2018, aerosol samples (PM10) were collected on quartz filter papers using a high-volume sampler (PM10) in Chennai, a semi-urban coastal environment located at 12.81°N, 80.03°E. These filter papers were stored under ambient laboratory conditions and were subsequently subjected to ultrasonication using ethanol as the solvent to separate the aerosols from the filters. The extracted samples were then analyzed using scanning electron microscopy (SEM) for the morphology and energy dispersive X-ray analysis (EDX) for elemental composition. The EDX analysis of the samples revealed the presence of various elements such as carbon (C), oxygen (O), aluminum (Al), silicon (Si), sulfur (S), potassium (K), iron (Fe), magnesium (Mg), calcium (Ca), vanadium (V), bismuth (Bi), sodium (Na), chlorine (Cl), phosphorus (P), and technetium (Tc). High concentrations of carbon, oxygen, and aluminum–silicate particles indicated the presence of carbonaceous aerosols and wind-blown dust particles. Concentration-weighted trajectory (CWT) analysis was carried out to assess the transport pathways of aerosols in the region. CALIPSO overpasses during the study period were selected, and the Vertical Feature Mask (VFM) identifiers for different aerosol types were compared with the local experimental results. The findings show that CALIPSO possess a reasonably effective capability in detecting and characterizing the local aerosol types. CALIPSO detected Dusty marine, Clean marine, Elevated smoke and Polluted dust in the study area across all four seasons. These findings closely match the characteristics of such aerosol types obtained from SEM/EDX analysis, HYSPLIT (HYbrid Single-Particle Lagrangian Integrated Trajectory) modeling, and the Angstrom exponent derived from sunphotometer readings.

Assessing Lidar Ratio Impact on CALIPSO Retrievals Utilized for the Estimation of Aerosol SW Radiative Effects across North Africa, the Middle East, and Europe

North Africa, the Middle East, and Europe (NAMEE domain) host a variety of suspended particles characterized by different optical and microphysical properties. In the current study, we investigate the importance of the lidar ratio (LR) on Cloud-Aerosol Lidar with Orthogonal Polarization–Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIOP-CALIPSO) aerosol retrievals towards assessing aerosols’ impact on the Earth-atmosphere radiation budget. A holistic approach has been adopted involving collocated Aerosol Robotic Network (AERONET) observations, Radiative Transfer Model (RTM) simulations, as well as reference radiation measurements acquired using spaceborne (Clouds and the Earth’s Radiant Energy System-CERES) and ground-based (Baseline Surface Radiation Network-BSRN) instruments. We are assessing the clear-sky shortwave (SW) direct radiative effects (DREs) on 550 atmospheric scenes, identified within the 2007–2020 period, in which the primary tropospheric aerosol species (dust, marine, polluted continental/smoke, elevated smoke, and clean continental) are probed using CALIPSO. RTM runs have been performed relying on CALIOP retrievals in which the default and the DeLiAn (Depolarization ratio, Lidar ratio, and Ångström exponent)-based aerosol-speciated LRs are considered. The simulated fields from both configurations are compared against those produced when AERONET AODs are applied. Overall, the DeLiAn LRs leads to better results mainly when mineral particles are either solely recorded or coexist with other aerosol species (e.g., sea-salt). In quantitative terms, the errors in DREs are reduced by ~26–27% at the surface (from 5.3 to 3.9 W/m2) and within the atmosphere (from −3.3 to −2.4 W/m2). The improvements become more significant (reaching up to ~35%) for moderate-to-high aerosol loads (AOD ≥ 0.2).

Analysis of Aerosol Types and Vertical Distribution in Seven Typical Cities in East Asia

Identifying the types and vertical distribution of aerosols plays a significant role in evaluating the influence of aerosols on the climate system. Based on the aerosol optical properties obtained from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), this study analyzed the long-term aerosol characteristics of seven cities in East Asia (Ulaanbaatar, Beijing, Lanzhou, Shanghai, Lhasa, Hong Kong, and Bangkok) from 2007 to 2021, including the spatiotemporal variations of aerosol optical depth (AOD), the vertical stratification characteristics of aerosols, and the main aerosol subtype. The results showed that, except for Lhasa, the AOD values of all cities exhibited a trend of initially increasing and then decreasing over the years. Except for Shanghai, the high values of AOD in the other cities occurred in the spring and summer seasons, while the low values occurred in the autumn and winter seasons. In all four seasons, the AOD contribution within the 1–3 km range accounted for more than 50% of the total. In the autumn and winter seasons, this proportion reached over 80%. The main types of aerosols and their contributions varied at different altitudes. Overall, dust, polluted continental/smoke, polluted dust, and elevated smoke dominated in all aerosol layers across each city. On the other hand, clean marine, clean continental, and dusty marine had very small proportions, accounting for less than 5% of all the cities’ aerosol layers.

A Regional Aerosol Model for the Middle Urals Based on CALIPSO Measurements

The present work aims to develop a regional Middle Urals Aerosol model (MUrA model) based on the joint analysis of long-term ground-based photometric measurements of the Aerosol Robotic NETwork (AERONET) and the results of lidar measurements of the CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) satellite relying on information on the air trajectories at different altitudes calculated using the HYSPLIT (Hybrid Single Particle Lagrangian Integrated Trajectory model) software package. The MUrA model contains parameters of normalized volume size distributions (NVSDs) characterizing the tropospheric aerosol subtypes detected by the CALIPSO satellite. When comparing the MUrA model with the global CALIPSO Aerosol Model (CAMel), we found significant differences in NVSDs for elevated smoke and clean continental aerosol types. NVSDs for dust and polluted continental/smoke aerosol types in the global and regional models differ much less. The total volumes of aerosol particles along the atmospheric column reconstructed from satellite measurements of the attenuation coefficient at a wavelength of 532 nm based on the regional MUrA model and global CAMel are compared with the AERONET inversion data. The mean bias error for the regional model is 0.016 μm3/μm2, and 0.043 μm3/μm2 for the global model.

Distributions and Direct Radiative Effects of Different Aerosol Types in North China

Different aerosol types exhibit distinct radiative effects in different regions, attributed to their unique optical characteristics and regional distributions. This study focuses on North China, which is impacted by both natural and anthropogenic aerosols with high concentrations and a variety of aerosol types. While many studies on aerosol direct radiative effects have been conducted in this region, the majority have focused on a specific type of aerosol or overall aerosol, leaving limited research on the direct radiative effects and contributions of different aerosol types. In this study, we use CALIPSO satellite data from 2011 to 2020 to investigate concentrations and distributions of different aerosol types. The results reveal that dust, polluted dust, polluted continental/smoke, and elevated smoke are the dominant aerosol types in North China. Based on the radiative closure experiment, we systematically calculate the radiative effects of different aerosol types and their corresponding contributions to the energy budget by combining satellite data with the Fu–Liou radiative transfer model. The annual average net aerosol direct radiative effect (ADRE) of North China is −6.1 and −13.43 W m−2 at the TOA and surface, respectively, causing a net warming effect of 7.33 W m−2 in the atmosphere. For each main aerosol type, dust contributes 93% to the shortwave ADRE in the western dust source region, while polluted dust mainly contributes 31% and 45% of the total ADRE, in Northwest China and North China Plain, respectively. Anthropogenic pollutant aerosols account for 58% of the total ADRE in Northeast China. This study holds great significance in elucidating the dominant aerosol types and their concentrations in North China, comprehending the impacts of different aerosol types on the local energy balance.

Analysis of Long‐Term Trends in the Vertical Distribution and Transport Paths of Atmospheric Aerosols in Typical Regions of China Using 15 Years of CALIOP Data

AbstractLong‐range transport and vertical distribution of aerosols are important factors for assessing the uncertainty in aerosol radiative forcing. This paper reveals the vertical distribution and trends of aerosol optical properties in China using 15 years of Cloud‐Aerosol Lidar with Orthogonal Polarization (CALIOP) data. The Hybrid Single‐Particle Lagrangian integrated trajectory model was used to analyze the transport and trends of aerosols in the layer with the highest occurrence frequencies of dust, polluted dust, polluted continental and elevated smoke aerosols. The results indicated that (a) there were significant regional and seasonal differences in the vertical distribution of aerosols. The aerosol optical depth (AOD) trend in a given region depends on the changes in the aerosol type with the highest frequency and the layer corresponding to the largest AOD in the vertical profile. The frequency of polluted dust aerosols was the highest in Beijing‐Tianjin‐Hebei (BTH) and Central China. The considerable decrease in the 0–2 km AOD led to a significant trend of the column AOD. (b) The changes of AOD and main aerosol types in a region are also affected by the changes of aerosol sources and long‐range transport pathways. In the BTH, dust aerosols originated from the Mongolian Plateau, accounting for 57.88% of the total trajectories. The Pearl River Delta was dominated by elevated smoke aerosols, with trajectories mainly originating from the Myanmar and Vietnam, accounting for 27.38% and 29.59%, respectively. The trend of 15‐year backward trajectories of dust aerosols on the Tibetan Plateau indicated that the trajectory from India is increasing.

Aerosol Optical Properties and Types over Southern Africa and Reunion Island Determined from Ground-Based and Satellite Observations over a 13-Year Period (2008–2021)

Fires occur seasonally in Southern Africa, from June to November, increasing tropospheric aerosol loading and triggering harmful consequences for the environment and human health. This study aims to examine 13 years of aerosol optical characteristics and types over Southern Africa and Reunion Island. Using AERONET sun photometers and MODIS observations, we found that a high aerosol optical depth and Angström exponent are associated with two predominant types of aerosols (biomass burning/urban industrial and mixed type) throughout the spring season. According to CALIOP observations, the major aerosol types with occurrence frequencies above 10% are polluted continental/smoke, polluted dust, and elevated smoke, whereas dust, clean continental, and dusty marine have occurrence frequencies below 1%. In comparison to other seasons, the vertical profiles of elevated smoke have different shapes in spring, with a seasonal shift in the peak altitude (from 3–4 km), when fire activity is at its maximum. At these altitudes, the northern regions presented occurrence frequencies of 32% on average, while lower values were found for the southern or farthest regions (<10–20% on average). The Lagrangian HYSPLIT model back-trajectories demonstrated eastward transport, with air masses from South America and the Atlantic Ocean that recirculate around the study sites. The aerosols are mainly derived from active biomass burning areas near the study sites and, to a lesser extent, from remote sources such as South America.

Aerosol Characterization of Northern China and Yangtze River Delta Based on Multi-Satellite Data: Spatiotemporal Variations and Policy Implications

Horizontal and vertical distributions of aerosol properties in the Taklimakan Desert (TD), North central region of China (NCR),North China Plain(NCP), and Yangtze River Delta (YRD) were investigated by statistical analysis using Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) L3 data from 2007 to 2020, to identify the similarities and differences in atmospheric aerosols in different regions, and evaluate the impact of pollution control policies developed in China in 2013 on aerosol properties in the study area. The aerosol optical depth (AOD) distribution had substantial seasonal and spatial distribution characteristics. AOD had high annual averages in TD (0.38), NCP (0.49), and YRD (0.52). However, these rates showed a decline post-implementation of the long-term pollution control policies; AOD values declined by 5%, 13.8%, 15.5%, and 23.7% in TD, NCR, NCP, and YRD respectively when comparing 2014–2018 to 2007–2013, and by 7.8%, 11.5%, 16%, and 10.4% when comparing 2019–2020 to 2014–2018. The aerosol extinction coefficient showed a clear regional pattern and a tendency to decrease gradually as height increased. Dust and polluted dust were responsible for the changes in AOD and extinction coefficients between TD and NCR and NCP and YRD, respectively. In TD, with change of longitude, dust aerosol first increased and then decreased gradually, peaking in the middle. Similarly in NCP, polluted dust aerosol first increased and then decreased, with a maximum value in the middle. The elevated smoke aerosols of NCP and YRD were significantly higher than those observed in TD and NCR. The high aerosol extinction coefficient values (>0.1 km−1) were mainly distributed below 4 km, and the relatively weak aerosol extinction coefficients (>0.001 km−1) were mainly distributed between 5–8 km, indicating that the high-altitude long-range transport of TD and NCR dust aerosols affects NCP and YRD.

Satellite-Observed Four-Dimensional Spatiotemporal Characteristics of Maritime Aerosol Types over the Coastal Waters of the Guangdong–Hong Kong–Macao Greater Bay Area and the Northern South China Sea

Aerosol is important to climate and air pollution, and different aerosol types have a non-negligible impact on the environment and climate system. Based on long-term satellite lidar profiles from 2006 to 2020, the four-dimensional (x-y-z-t) spatiotemporal characteristics of different aerosol types, including clean marine (CM), dust (DU), polluted continental/smoke (PC), clean continental (CC), polluted dust (PD), elevated smoke (ES), and dusty marine (DM), over the coastal waters of the Guangdong–Hong Kong–Macao Greater Bay Area (GBA) were revealed for the first time and compared to the surrounding northern South China Sea (NSCS). (1) The dominant aerosol types in both study areas were found to be CM, ES, and DM, whose proportions summed up to more than 85%. In spring, ES was the dominant aerosol type (>40%); in other seasons, CM dominated (>34%). The proportions of anthropogenic aerosols (PC, PD, and ES) and dust-related aerosols (DU, PD, and DM) were higher in spring and winter than in summer and autumn. (2) Vertically, the number of all aerosol types declined with increasing altitude, with the exception of abnormal increase at the heights of approximately 1.5–2.8 km in spring, which was probably attributed to the effect of local and regional anthropogenic pollutants. Below the height of 2 km, the main aerosol types were CM and DM, whereas ES, PD, and DU aerosols were dominant above 2 km. (3) Horizontally, the dominant aerosol types were spatially uniform in the lower atmosphere (<2 km), while higher altitudes (especially > 4 km) showed significant horizontal heterogeneity in space. The proportion of anthropogenic aerosols over the coastal waters of the GBA was higher than that over the NSCS, due to terrestrial pollution transportation. (4) In terms of the long-term trend, the proportion of CM aerosols was found to be steadily increasing, with the anthropogenic aerosols and dust-related aerosols showing a fluctuating and decreasing trend, which resulted from the enforcement of effective air pollution control policies. Overall, the terrestrial aerosol influence tended to decrease in the study areas. The insight into aerosol types and its variation will facilitate the understanding of the aerosol climate effects and pollutant control in the coastal waters of the GBA and the NSCS.

Identifying Seasonal and Diurnal Variations and the Most Frequently Impacted Zone of Aerosols in the Aral Sea Region.

With the desiccation of the Aral Sea, salt-alkali dust storms have increased in frequency and the surrounding environment has deteriorated. In order to increase our understanding of the characteristics and potential impact zone of atmospheric aerosols in the Aral Sea region, we evaluated seasonal and diurnal variation of aerosols and identified the zone most frequently impacted by aerosols from the Aral Sea region using CALIPSO data and the HYSPLIT model. The results showed that polluted dust and dust were the two most commonly observed aerosol subtypes in the Aral Sea region with the two accounting for over 75% of observed aerosols. Occurrence frequencies of polluted dust, clean continental, polluted continental/smoke, and elevated smoke showed obvious seasonal and diurnal variations, while occurrence frequency of dust only showed obvious seasonal variation. Vertically, the occurrence frequencies of all aerosol subtypes except dust showed significant diurnal variation at all levels. The thickness of polluted dust layers and dust layers exhibited same seasonal and diurnal variations with a value of more than 1.0 km year-round, and the layer thickness of clean continental and polluted continental/smoke shared the same seasonal and diurnal variation features. The zone most severely impacted by aerosols from the Aral Sea region, covering an area of approximately 2 million km2, was mainly distributed in the vicinity of the Aral Sea region, including western Kazakhstan, and most of Uzbekistan and Turkmenistan. The results provide direct support for positioning monitoring of aeolian dust deposition and human health protection in the Aral Sea region.

Why do extreme particulate pollution events occur in low-emission Yunnan Province, China?

Yunnan Province in southwest China has low anthropogenic emissions, but in recent years it encountered unprecedented serious particulate pollution. To clarify the causes of pollution in this province, this study comprehensively analyzed the spatial-temporal distribution of near-surface PM2.5 (particles with aerodynamic diameter less than 2.5 μm) from 2017 to 2021, which was retrieved from Himawari-8 aerosol optical depth. The results show that, particulate pollution mainly occurred in the dry season (November to April), especially in March and April. And the heavily polluted areas mainly distributed in the southwest of the province, where there is small population and high forest cover. Dust, polluted dust, and elevated smoke were the most spatio-temporally variable aerosols, which should be attributed to biomass combustion and polluted air mass transportation from neighboring countries. The comparisons between effects of anthropogenic emissions, stable weather and pollutant transportation on local air quality indicate that exogenous pollutants should be mainly responsible for the concentrated outbreak of particulate pollution in Yunnan Province during the second half of the dry season. Besides, the stable weather conditions would further aggravate the deterioration of air quality. This study provides important reference for further strengthening joint prevention and control of regional air pollution.

Observational evidence of elevated smoke layers during crop residue burning season over Delhi: Potential implications on associated heterogeneous PM2.5 enhancements

Post monsoonal agricultural Crop Residue Burning (CRB) over northwestern India is believed to severely affect the air quality of the megacity of Delhi. However, the mechanistic understanding remains elusive. Long-term satellite observations (2007–2020) of aerosol properties during CRB season (Oct 20th to Nov 20th) indicate a distinct airshed of CRB plume transport from Northwestern India (source region) to greater Delhi (downwind region). Theoretically, the smoke concentration should disperse downwind, and the CRB-associated PM2.5 enhancement over Northern India should be inversely proportional to the distance from the CRB source region. However, the in-situ PM2.5 observations illustrate that smoke-associated enhancement in PM2.5 over greater Delhi (downwind region) is disproportionately large compared to the source region. In this study, we examine satellite, radiosonde, and ground-based observations along with reanalysis data to provide robust evidence that aerosol- boundary layer - PM2.5 associations via semi-direct effect can explain the above heterogeneity. Vertically resolved satellite observations indicate that as the emitted CRB-smoke plumes travel downwind, a portion of the transported smoke plume injected relatively at a higher altitude leads to the formation of an elevated smoke layer over greater Delhi. These elevated smoke layers tend to suppress the mixing height via inducing strong temperature inversion, thereby severely constraining the daytime dilution effect of shallow boundary layers. Along with direct advection of smoke particles, enhanced accumulation of local urban emissions due to these semi-direct impacts can lead to the observed disproportionate PM2.5 enhancements over Delhi during CRB haze periods. Thus, control of the local anthropogenic emissions could bring relief during the extreme haze episodes over Delhi.

Characterizing aerosols during forest fires over Uttarakhand region in India using multi-satellite remote sensing data

Confirmed rise in average surface temperature and consequent prolonged dry days in tropical Himalayan foothills (tarai region) favors frequent wildfire event which make susceptible to the local forest vegetation and ecology. Recent improvement in spatio-temporal resolution of space-borne sensors provides an opportunity to routinely map these wildfires and estimate the consequence. Utilizing both active and passive space-borne multi-sensors, this study presents the active fire counts, columnar and vertical distribution of aerosol during 2013–2018 over Uttarakhand region of India. Our analysis shows maxima in active fire counts during April to late June months while minima in monsoon over the region. Particularly owing to the high temperature, low moisture, drying up of natural spring and availability of fuel materials in summer and scare precipitation in winter. Some limited spatio-temporal scale fire episodes are also marked in winter. The AOD values with maximum of 3.2 (0.5 mean) observed during the April 2016, while for the successive next two months, AOD of 2.0 and 1.2 are found over the fire burning regions. The Normalized Burn Ratio Thermal (NBRT) index are also found to be much higher for April and May 2016 with respect to 2015 and 2017. The comparative analysis of NBRT shows a positive difference towards the western side of Uttarakhand. Vertical feature mask and aerosol subtype profile details about the polluted dust and elevated smoke aerosols from surface to 10 km range during the intense fire events smoke were elevated and trapped within 3 to 10 km. The results demonstrate the potential of earth’s observing satellites for characterization of emissions and in air quality management.

Assessment of tropospheric CALIPSO Version 4.2 aerosol types over the ocean using independent CALIPSO–SODA lidar ratios

Abstract. We assess the CALIPSO Version 4.2 (V4) aerosol typing and assigned lidar ratios over ocean using aerosol optical depth (AOD) retrievals from the Synergized Optical Depth of Aerosols (SODA) algorithm and retrieved columnar lidar ratio estimated by combining SODA AOD and CALIPSO attenuated backscatter (CALIPSO–SODA). Six aerosol types – clean marine, dusty marine, dust, polluted continental/smoke, polluted dust, and elevated smoke – are characterized using CALIPSO–SODA over ocean and the results are compared against the prescribed V4 lidar ratios, when only one aerosol type is present in the atmospheric column. For samples detected at 5 or 20 km spatial resolutions and having AOD > 0.05, the CALIPSO–SODA lidar ratios are significantly different between different aerosol types, and are consistent with the type-specific values assigned in V4 to within 10 sr (except for polluted continental/smoke). This implies that the CALIPSO classification scheme generally categorizes specific aerosols types correctly over regions where they are abundant. We find remarkable daytime/nighttime regional agreement for clean marine aerosol over the open ocean (CALIPSO–SODA = 20–25 sr, V4 = 23 sr), elevated smoke over the southeast Atlantic (CALIPSO–SODA = 65–75 sr, V4 = 70 sr), and dust over the subtropical Atlantic adjacent to the African continent (CALIPSO–SODA = 40–50 sr, V4 = 44 sr). In contrast, daytime polluted continental/smoke lidar ratio is more than 20 sr smaller than the constant V4 value for that type, attributed in part to the challenge of classifying tenuous aerosol with low signal-to-noise ratio. Dust over most of the Atlantic Ocean features CALIPSO–SODA lidar ratios less than 40 sr, possibly suggesting the presence of dust mixed with marine aerosols or lidar ratio values that depend on source and evolution of the aerosol plume. The new dusty marine type introduced in V4 features similar magnitudes and spatial distribution as its clean marine counterpart with lidar ratio differences of less than 3 sr, and nearly identical values over the open ocean, implying that some modification of the classification scheme for the marine subtypes is warranted.

Constrained Retrievals of Aerosol Optical Properties Using Combined Lidar and Imager Measurements During the FIREX-AQ Campaign

Smoke aerosols arise from a variety of regional sources and fuel types dependent on the properties of the fire, leading to spatial variability in smoke composition and optical properties. After emission, these aerosols age and mix in the atmosphere with other aerosol species, such as sulfates, altering the optical, and microphysical properties of the smoke aerosols over time. Thus, lidar ratio (extinction to backscatter ratio) derived from lidar sensors exhibit spatiotemporal variability for smoke. Traditional backscatter lidar processing algorithms employ a signal loss method that utilizes the reduction of signals below and above cloud layers, enabling simultaneous retrievals of both layer-averaged lidar ratio and particulate extinction, which avoids the need for assigning lidar ratios based on layer type as is typically used for backscatter lidar algorithms. In this study, the signal loss method, which is traditionally designed for cloud property retrievals, is attempted for elevated smoke plume property retrievals using NASA’s Cloud Physics Lidar (CPL) observations from the 2019 Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) field campaign. Good agreement (linear correlation coefficient of 0.67) is found between aerosol optical depth (AOD) derived from the signal loss method and the constrained method, utilizing collocated GOES MAGARA AOD values as constraints for lidar ratio retrievals, for the Williams Flats smoke event. Differences in derived lidar ratios from the signal loss method and the constrained method (13.6 and 7.4%) are found to be smaller than the expected signal loss lidar ratio error estimate of ∼17–23%. A good agreement is also found in lidar ratios derived from this study and from using Differential Absorption Lidar-High Spectral Resolution Lidar (DIAL-HSRL) measurements for the Williams Flats Fire. The lidar ratio statistics of smoke plumes presented in this analysis (51 ± 13 sr) also compare favorably with lidar ratio values found in previous studies; however, they remain lower than the assumed smoke lidar ratio of 70 sr (at 532 nm) used by CALIPSO and CPL, and vary with plume transport distance. These findings suggest lidar ratio is likely to be regionally specific and evolve with plume transport. Thus, innovative methods for simultaneous retrieval of lidar ratio and aerosol extinction, such as the signal loss method proposed in this study, are needed for accurate aerosol retrievals from standard backscatter lidars in the future.

Experimental and computational studies on the effects of reduced fuel injection pressure and spark plug protrusion on the performance and emissions of a small-bore gasoline direct-injection engine

Application of direct injection (DI) technology in small-bore engines, the type used in two- and three-wheelers, could improve their performance significantly. It is recognised that the use of high fuel injection pressure is beneficial in large-bore engines for a good mixture preparation. However, simple systems incorporated with low-pressure DI are desirable in small-engine segment of automobiles. Further, high fuel pressures will result in excessive wall wetting when cylinder dimensions are small. Extensive studies were carried out to investigate the minimum fuel injection pressure required for homogeneous and lean modes of operation in such small bore DI engine. The effect of spark plug protrusion in the combustion chamber was also investigated under the spray-guided configuration. Comprehensive experiments and CFD simulations were performed for estimating the engine efficiency, emissions, mixture preparation characteristics, fuel spray and fuel impingement on combustion chamber walls. Results have demonstrated that engine performance and emissions did not deteriorate when fuel injection pressure was reduced from 150 to 50 bar at full load. However, at very low pressures, like 20–30 bar, THC, CO and smoke emissions increased. Fuel injection pressure did not influence the lean limit, that is, equivalence ratio of about 0.77, but influenced the thermal efficiency at lean conditions. In order to attain high efficiency, under lean conditions, a minimum fuel pressure of 80 bar was required. The spark plug protrusion that resulted in a gap of 0.75 mm with respect to the incoming fuel spray cone has given the best engine performance, while higher protrusions affected the tumble flow and led to the stratification of charge near the spark plug, which resulted in elevated CO and smoke emissions. Hence, this work highlights that relatively lower direct injection pressures are suitable in small bore engines, which will impact the development of cost effective components for such applications.

An Overview of Aerosol Properties in Clear and Cloudy Sky Based on CALIPSO Observations

AbstractA full understanding of the climatological properties of aerosols is an important step towards characterizing their effects on climate. Utilizing the observations from Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observations, we study cloud‐free and cloudy aerosol properties with attention on aerosol and cloud layer relative vertical positions. On a global scale, the cloud‐free aerosols account for about 56% of all detected aerosols with a mean optical depth () and mean uncertainty of 0.135 ± 0.047. The cloudy aerosols, accounting for 44%, have a larger and larger mean uncertainty of 0.143 ± 0.074 compared to the cloud‐free aerosols. The above‐cloud aerosols (∼4%), primarily composed of elevated smoke, dust/volcanic ash and polluted dust, have a much smaller of (0.056 ± 0.038). The below‐cloud aerosols (∼21%) have ∼ 0.165 0.087. The below‐cloud and cloud‐free aerosols show close probability density distributions and similar aerosol types, indicating that cloud‐free aerosol climatologies from passive sensors are likely representative of all‐sky conditions. In addition, about 27% of the detected aerosol profiles are found to have cloud layers vertically connected to the detected aerosol layers. The lidar backscatter profiles of these aerosols have larger median values than the cloud‐free, above‐cloud and below‐cloud aerosols. The seasonal variations of the cloud‐free and the cloudy aerosols significantly vary with regions. Our results imply that quantifying the impact of clouds, particularly cirrus due to the wide coverage of cirrus‐aerosol overlap, on aerosol direct radiative effect is crucial to assess aerosols' roles in the Earth‐climate system.

Assessing the benefits of Imaging Infrared Radiometer observations for the CALIOP version 4 cloud and aerosol discrimination algorithm

Abstract. The features detected in monolayer atmospheric columns sounded by the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and classified as cloud or aerosol layers by the CALIOP version 4 (V4) cloud and aerosol discrimination (CAD) algorithm are reassessed using perfectly collocated brightness temperatures measured by the Imaging Infrared Radiometer (IIR) aboard the same satellite. Using the IIR's three wavelength measurements of layers that are confidently classified by the CALIOP CAD algorithm, we calculate two-dimensional (2-D) probability distribution functions (PDFs) of IIR brightness temperature differences (BTDs) for different cloud and aerosol types. We then compare these PDFs with 1-D radiative transfer simulations for ice and water clouds and dust and marine aerosols. Using these IIR 2-D BTD signature PDFs, we develop and deploy a new IIR-based CAD algorithm and compare the classifications obtained to the results reported by the CALIOP-only V4 CAD algorithm. IIR observations are shown to be able to identify clouds with a good accuracy. The IIR cloud identifications agree very well with layers classified as confident clouds by the V4 CAD algorithm (88 %). More importantly, simultaneous use of IIR information reduces the ambiguity in a notable fraction of “not confident” V4 cloud classifications. 28 % and 14 % of the ambiguous V4 cloud classifications are reclassified more appropriately as confident cloud layers through the use of the IIR observations in the tropics and in the midlatitudes, respectively. IIR observations are of relatively little help in deriving high-confidence classifications for most aerosols, as the low altitudes and small optical depths of aerosol layers yield IIR signatures that are similar to those of clear skies. However, misclassifications of aerosol layers, such as dense dust or elevated smoke layers, by the V4 CAD algorithm can be corrected to cloud layer classification by including IIR information. 10 %, 16 %, and 6 % of the ambiguous V4 dust, polluted dust, and tropospheric elevated smoke, respectively, are found to be misclassified cloud layers by the IIR measurements.

The CALIPSO retrieved spatiotemporal and vertical distributions of AOD and extinction coefficient for different aerosol types during 2007–2019: A recent perspective over global and regional scales

In the present study, we investigated the global climatology of the spatiotemporal and vertical distributions of aerosol optical properties for different aerosol types, mainly including total aerosols (All), desert dust (DD), polluted dust (PD), and elevated smoke (ES). The data used for the study is derived from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) for Research and Application. We found that the seasonal distribution of the global mean aerosol optical depth (AOD) of All type in the land area are in the order JJA (0.157) > MAM (0.134) > DJF (0.127) > SON (0.124). This is attributed to the more frequent sand and dust activities over the Taklimakan Desert and the Sahara Desert in MAM and JJA. Owing to the transportation of DD, ES, and PD from the aerosol source, the ocean areas (especially for downwind regions) present the high AOD, and with the same seasonal distribution trend as in the land area. Also, the mean extinction coefficient (EC) for all aerosols decreases with the increase of height in all seasons for both hemispheres. The maximum mean EC for All aerosols is 0.0102 km−1 (0.016 km−1) during the day (night) in DJF (JJA) in the northern hemisphere, while the maximum is 0.006 km−1 (0.008 km−1) during the day (night) in JJA (SON) in the southern hemisphere. Also, the occurrence of frequencies of DD, PD, and ES aerosols are distributed throughout the entire troposphere in all seasons, but the clean marine (CM) and polluted continent (PC) are mostly below 3 km.

Type‐Dependent Impact of Aerosols on Precipitation Associated With Deep Convective Cloud Over East Asia

AbstractAerosol‐cloud‐precipitation interactions represent one of the most significant uncertainties in climate simulation and projection. In particular, the impact of aerosols on precipitation is highly uncertain due to limited and conflicting observational evidence. A major challenge is to distinguish the effects of different types of aerosols on precipitation associated with deep convective clouds, which produces most of the precipitation in East Asia. Here, we use 9‐yr observations from multiple satellite‐borne sensors and find that the occurrent frequency of heavy rain increases while that of light rain decreases with the increase of aerosol optical depth (AOD) for dust and polluted continental aerosol types. For average hourly precipitation amount, elevated smoke tends to suppress deep convective precipitation, while dust and polluted continental aerosols enhance precipitation mainly through the invigoration of deep convection. The invigoration effect is more significant for clouds with higher cloud base temperature (CBT), while no significant invigoration is observed when CBT is <12°C. A great contrast is found for the response of average hourly precipitation amount to aerosols over ocean and land. While the prevailing continental aerosol types other than smoke increase precipitation, the marine aerosols first enhance and then inhibit precipitation with the increase of AOD. Moreover, our analysis indicates that the above‐mentioned enhancement and inhibition effects on precipitation are mainly caused by aerosols themselves, rather than by the covariation of meteorological factors. These observed relationships between different aerosol types and precipitation frequency and amount provide valuable constraints on the model forecasting of precipitation.