Aerosol Products Research Articles

A similarity distance-based space-time random forest model for estimating PM2.5 concentrations over China

China has experienced persistent fine particulate matter (PM2.5) pollution for the past few years, which adversely affects both physical and mental health. The availability of high-accuracy and full-coverage PM2.5 products will be of substantial value in formulating effective policies to combat and regulate PM2.5 pollution. Therefore, we have developed a similarity distance-based space-time random forest (SDSTRF) model to estimate daily PM2.5 concentrations over China by integrating surface measurements, satellite aerosol products, meteorological data, and auxiliary information. The proposed model not only accounts for spatial-temporal heterogeneity, but also uses the similarity distance to avoid errors caused by outliers. It has undergone rigorous validation through three different cross-validation (CV) approaches and has shown high and stable accuracy, particularly in the site-based CV with a coefficient of determination (R2) of 0.87, and a root mean square error (RMSE) of 10.68 μg/m3, along with a relative RMSE (rRMSE) of 27.48%. In addition, the leave-out data are predicted to determine if the SDSTRF model is accurate in its predictive power, which achieves an impressive site-based CV R2 of 0.80 and an RMSE of 12.89 μg/m3, along with an rRMSE of 33.01%. The results from a variety of validation approaches strongly indicate that the SDSTRF model can provide accurate estimation of PM2.5 concentrations at different time scales and outperform many other space-time models by incorporating similarity distance. The proposed model would be a promising application in air pollution studies with remote sensing.

Disposable Dosators Intended for Dry Powder Delivery to Mice.

Dry powder inhalers offer numerous advantages for delivering drugs to the lungs, including stable solid-state drug formulations, device portability, bolus metering and dosing, and a propellant-free dispersal mechanism. To develop pharmaceutical dry powder aerosol products, robust in vivo testing is essential. Typically, initial studies involve using a murine model for preliminary evaluation before conducting formal studies in larger animal species. However, a significant limitation in this approach is the lack of suitable device technology to accurately and reproducibly deliver dry powders to small animals, hindering such models' utility. To address these challenges, disposable syringe dosators were developed specifically for intrapulmonary delivery of dry powders in doses appropriate for mice. These dosators load and deliver a predetermined amount of powder obtained from a uniform bulk density powder bed. This discrete control is achieved by inserting a blunt needle to a fixed depth (tamping) into the powder bed, removing a fixed quantity each time. Notably, this dosing pattern has proven effective for a range of spray-dried powders. In experiments involving four different model spray-dried powders, the dosators demonstrated the ability to achieve doses within the range of 30 to 1100 µg. The achieved dose was influenced by factors such as the number of tamps, the size of the dosator needle, and the specific formulation used. One of the key benefits of these dosators is their ease of manufacturing, making them accessible and cost-effective for delivering dry powders to mice during initial proof-of-concept studies. The disposable nature of the dosators facilitates use in animal procedure rooms, where cleaning and refilling reusable systems and weighing materials is inconvenient. Thus, developing disposable syringe dosators has addressed a significant hurdle in murine dry powder delivery for proof-of-concept studies, enabling researchers to conduct more accurate and reproducible preliminary studies in small animal models for pulmonary drug delivery.

Anthropogenic amplification of biogenic secondary organic aerosol production

Abstract. Biogenic secondary organic aerosols (SOAs) contribute to a large fraction of fine aerosols globally, impacting air quality and climate. The formation of biogenic SOA depends on not only emissions of biogenic volatile organic compounds (BVOCs) but also anthropogenic pollutants including primary organic aerosol, sulfur dioxide (SO2), and nitrogen oxides (NOx). However, the anthropogenic impact on biogenic SOA production (AIBS) remains unclear. Here we use the decadal trend and variability in observed organic aerosol (OA) in the southeast US, combined with a global chemistry–climate model, to better constrain AIBS. We show that the reduction in SO2 emissions can only explain 40 % of the decreasing decadal trend of OA in this region, constrained by the low summertime month-to-month variability in surface OA. We hypothesize that the rest of the OA decreasing trend is largely due to a reduction in NOx emissions. By implementing a scheme for monoterpene SOA with enhanced sensitivity to NOx, our model can reproduce the decadal trend and variability in OA in this region. Extending to a centennial scale, our model shows that global SOA production increases by 36 % despite BVOC reductions from the preindustrial period to the present day, largely amplified by AIBS. Our work suggests a strong coupling between anthropogenic and biogenic emissions in biogenic SOA production that is missing from current climate models.

Validation and diurnal variation evaluation of MERRA-2 multiple aerosol properties on a global scale

The Modern-Era Retrospective analysis for Research and Applications (MERRA-2) provides a spatiotemporal seamless simulation of global aerosol properties. This study focused on evaluating its diurnal AOD accuracy and variation and the performance of multi-aerosol properties (including Ångström exponent (AE), fine mode fraction (FMF), and single scattering albedo (SSA)) using AERONET measurements. The spatial distribution patterns of MERRA-2 AOD are compared with the MODIS (daytime) and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO, nighttime) satellite products, respectively. The results show that MERRA-2 AOD exhibits good agreement with AERONET AOD during daytime and nighttime, with a Pearson correlation coefficient (R) exceeding 0.785, and the fraction of meeting the expected error (EE) exceeding 0.705. The accuracy of daytime AOD is comparable to that of the MODIS AOD product. Furthermore, MERRA-2 AE and FMF have a higher accuracy than MODIS products, with an R > 0.840 and an RMSE of 0.313 for AE and 0.150 for FMF. And it effectively captures the diurnal variation of aerosol properties, with an R of 0.911, 0.392, and 0.72 for AOD, AE, and FMF at different times of day compared to AERONET. Additionally, MERRA-2's ability to characterize the spatial patterns of daytime and nighttime is comparable to those of satellite products. Overall, this study provides the usage references for MERRA-2 aerosol product, highlighting its high accuracy and ability to capture diurnal variation and spatial patterns.

COVID-19 transmission in dental practice: risks and prevention – narrative review

Dentists are on the frontline of infection, especially regarding respiratory viruses like the new coronavirus. The production of aerosols and droplets accompanies many dental procedures. The emergence of severe acute air-droplet disease, respiratory syndrome, or SARS, warrants a revision of the infection control procedures for aerosols.
 The aim. In this article, we aim to raise awareness of the potential risks of COVID-19 transmission in dental practice and discuss and suggest some preventive measures.
 Methods. This study reviewed the published research articles and the guidelines of international healthcare institutions on dentistry and COVID-19. We searched Pubmed, Web of Science, and SCOPUS electronic databases using MESH terms.
 Results. The main way of transmission of the SARS CoV is air-droplet. Thus, healthcare professionals that perform aerosol-generating procedures, i.e. dentists, need to be updated about the origin of the disease. The patient and the dentist often share close contact while ongoing dental treatment; thus, knowledge about the disease and necessary preventive measures is required. In addition to the standard precautions, some special preventive measures that should be implemented during an outbreak of disease have been raised in this review.
 Conclusions. Following the protective protocols in the COVID-19 crisis is of utmost importance in a dental setting

Improving atmospheric CO2 retrieval based on the collaborative use of Greenhouse gases Monitoring Instrument and Directional Polarimetric Camera sensors on Chinese hyperspectral satellite GF5-02

ABSTRACT The Greenhouse Gas Monitoring Instrument (GMI) onboard the Chinese hyperspectral satellite GF5–02 can provide abundant observations of global atmospheric CO2, which plays an important role in climate research. CO2 retrieval precision is the key to determining the application value of the GMI. To reduce the influence of atmospheric scattering on retrieval, we combined the Directional Polarimetric Camera (DPC) data on the same satellite to improve the anti-interference ability of GMI CO2 retrieval and ensure its retrieval precision. To realize the reliability and feasibility of the collaborative use of the GMI and DPC, this paper designs the pointing registration method of the GMI based on coastline observations, the spatial resolution matching method and the collaborative cloud screening method of the GMI and DPC observations. Combined with the DPC, which supplied the spectral data and aerosol product, the retrieval ability of the coupled bidirectional reflectance distribution function CO2 retrieval (CBCR) method developed for GMI CO2 retrieval was improved, with the retrieval efficiency of CO2 products increasing by 27%, and the CO2 retrieval precision increasing from 3.3 ppm to 2.7 ppm. Moreover, collaborative use not only guaranteed the GMI’s ability to detect global and area CO2 concentration distribution characteristics, such as significant concentration differences between the Northern and Southern Hemispheres in winter and high CO2 concentrations in urban agglomeration areas caused by human activities, but also extended the GMI’s potential for monitoring anomalous events, such as the Tonga volcanic eruption.

Fractionation as the main method for smoked tobacco products identification

Smokeless tobacco products are products that do not require a pyrolysis process and / or the production of tobacco aerosol (smoke) at the time of use. In the absence of data on the toxicological risks of smokeless tobacco, their consumption is potentially on the rise. The variety of non-smoking tobacco products creates certain problems in identifying chewing tobacco and sucking tobacco (banned for sale in the Russian Federation) as products that are identical in terms of physiological effects, method of consumption, and component composition. A methodology has been developed for a comprehensive assessment of non-smoking products, including the determination of consumer properties and technological indicators by instrumental methods, as well as the determination of the level of toxic components (nicotine, TSNA, B(a)P). The difference between the types of smokeless tobacco is mainly in the granulometric composition of the product: snus – finely ground tobacco, chewing tobacco – snatches of tobacco with a removed middle vein. Identification indicators have been determined: the presence of raw tobacco, the size of its particles and the number of large fragments in the finished product. The presence of raw tobacco can be determined by optical microscopy and/or luminescent analysis, and the quantitative content can be determined by sieve analysis. The quantitative content of the coarse fraction in chewing tobacco (not less than 15 %) is the main indicator of the product. The use of the fractionation method makes it possible to differentiate between sucking and chewing tobacco. A «Method for determining the fractional composition of non-smoking tobacco products for oral consumption by the method of sieve analysis» was developed (Certificate No. 022-01.00281-2013-2022). To certify the methodology, a set of studies was carried out, the data were obtained as a result of five parallel measurements by three performers for each sample. The technique is registered in the State Register of Measuring Instruments (FR.1.31.2022.43935 of 09/02/2022). Technological indicators of SLT samples were established: humidity (11,4-53,3) %, pH level 5,7-9,7, coarse fraction content (0,4-56,9) %, dust fraction content (0,2-76,3) %. The results of identification of commercial samples of a segmental product are presented.

Ciechocinek Spa — the Biggest Health Resort in the Polish Lowlands in Terms of Geotourism

Ciechocinek is known for its unique saline graduation towers and salt works. The crucial date in Ciechocinek’s history was 1836, when four treatment copper bath tubs were installed in the local inn. This gave rise to the beginning of the Health Springs Enterprise, which was the origin of the Health Resort. The graduation towers of Ciechocinek are particular and they are the biggest wooden constructions which serve to vaporize brine’s water from the spring no. 11. The graduation towers were built in the shape of a horseshoe. Two first graduation towers were built in the years between 1824 and 1828 and the third in 1859. The height of towers is about 15.8 m and the total length of all of them is more than 1741.5 m. They constitute a unique monument of the nineteenth-century technology, one of few in Europe. In the graduation towers the concentration of salt brine takes place as a part of the salt production process. A characteristic feature of this process is the production of a natural aerosol with healing properties. Within the graduation towers there is a specific microclimate, a natural and curative inhaler. The technology of salt production, which is based on heating concentrated salt brine, has not changed in 190 years — it consists in heating concentrated brine. Thermal brines of the Na–Cl type and J type from borehole no. 14 (Terma 14) and borehole no. 16 (Terma 16) are used for Ciechocinek Spa mineral water supply. These boreholes are screened in the Dogger and Lias sandstones. The water in Terma 14 has mineralization (total dissolved solids (TDS)) of 43.5 g/L and the temperature on the borehole outflow is 28 °C. The water from Terma 16 has mineralization (TDS) of 53.4 g/L. It is thermal water and its temperature on the borehole outflow is 32 °C. The therapeutic thermal water in the Ciechocinek boreholes occurs at considerable depth and its resources are very slowly renewable. The therapeutic qualities of Ciechocinek springs are strongly recommended for curing cardiovascular, respiratory, orthopedic, traumatic, rheumatic, nervous system, and women’s diseases. The Ciechocinek Spa is a producer of well-known products of perfect quality: “Krystynka” mineral water, flavored water, table salt, medicinal lye, and mud.

Acoustic resonance effects and cavitation in SAW aerosol generation

The interaction of surface acoustic waves (SAWs) with liquids enables the production of aerosols with adjustable droplet sizes in the micrometer range expelled from a very compact source. Understanding the nonlinear acousto-hydrodynamics of SAWs with a regulated micro-scale liquid film is essential for acousto-microfluidics platforms, particularly aerosol generators. In this study, we demonstrate the presence of micro-cavitation in a MHz-frequency SAW aerosol generation platform, which is touted as a leap in aerosol technology with versatile application fields including biomolecule inhalation therapy, micro-chromatography and spectroscopy, olfactory displays, and material deposition. Using analysis methods with high temporal and spatial resolution, we demonstrate that SAWs stabilize spatially arranged liquid micro-domes atop the generator's surface. Our experiments show that these liquid domes become acoustic resonators with highly fluctuating pressure amplitudes that can even nucleate cavitation bubbles, as supported by analytical modeling. The observed fragmentation of liquid domes indicates the participation of three droplet generation mechanisms, including cavitation and capillary-wave instabilities. During aerosol generation, the cavitation bubbles contribute to the ejection of droplets from the liquid domes and also explain observed microstructural damage patterns on the chip surface eventually caused by cavitation-based erosion.

Optical and Physical Characteristics of Aerosol Layers in Australia Based on CALIPSO

Atmospheric aerosols have important impacts on global radiative forcing, air pollution, and human health. This study investigated the optical and physical properties of aerosol layers over Australia from 2007 to 2019 using the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) Level 2 aerosol products. Australia was divided into three sub-regions (western highlands, central plains, and eastern ranges). Interannual and seasonal optical property variations in aerosol layers in the three sub-regions were analyzed and compared. Results showed that annual mean values of AODL (lowest aerosol layer AOD) and AODT (total AOD of all aerosol layers) were always higher in the eastern ranges region than the other two regions from 2007 to 2019. The reason could be that Australian population was predominantly located in the eastern ranges region, where more human activities could bring significant aerosol loadings. BL (base height of the lowest aerosol layer), HL (top height of the lowest aerosol layer), and HH (top height of the highest aerosol layer) all showed trends of “western highlands > eastern mountains > central plains”, indicating that the higher the elevation, the higher the BL, HL, and HH. TL (thickness of the lowest aerosol layer) was higher during the day than at night, which might account for increased diurnal atmospheric convection and nocturnal aerosol deposition. DRL (depolarization ratio of the lowest aerosol layer) was higher in the western highlands and central plains than the eastern mountains, probably because these two regions have large deserts with more irregularly shaped dust aerosols. CRL (color ratio of the lowest aerosol layer) had slightly higher values in the eastern ranges than the other two regions, probably due to the wet climate of the eastern ranges, where aerosols were more hygroscopic and had larger particle sizes. This study can provide technical support for the control and management of regional air pollutants.

Efficient modulated acoustic nebulisation for aerosol delivery and detection of plasma-activated water for surface disinfection and decontamination

Chipscale surface and bulk acoustic nebulisers offer an efficient means for in situ production of plasma-activated aerosols for portable surface disinfection, although their adoption in practice is hampered by the low nebulisation rates that impose limits on the throughput and scalability of the platform. We demonstrate in this work the possibility of increasing the nebulisation rate of three different high frequency acoustic nebulisation platforms driven by surface, bulk (thickness mode) and hybrid (surface and bulk) acoustic waves through a unique hybrid modulation excitation scheme involving a combination of amplitude and pulse-width modulation. In particular, we show that such a hybrid modulation scheme provides stable nebulisation while maintaining the aerosol characteristics of these platforms, while substantially increasing the maximum peak surface acceleration on the piezoelectric substrate to yield efficiency gains in the nebulisation rate by up to 243%, albeit only over short intervals across a complete frequency cycle so as to limit increases in temperature that can be damaging to the device. While the hybrid modulation scheme works best with the SAW nebulisation platform, we also show the possibility of exploiting the bulk (Lamb) acoustic waves for detection of the electrical conductivity (>95% prediction accuracy via the neutral network) and hence ionic conductivity of the plasma-activated water, thereby facilitating the potential for concurrent detection during dispensing of the plasma-activated aerosols for disinfection in a low-cost portable integrated device that employs a common piezoelectric substrate material.

Aerosol optical depth retrieval from the EarthCARE Multi-Spectral Imager: the M-AOT product

Abstract. The Earth Explorer mission Earth Clouds, Aerosols and Radiation Explorer (EarthCARE) will not only provide profile information on aerosols but also deliver a horizontal context to it through measurements by its Multi-Spectral Imager (MSI). The columnar aerosol product relying on these passive signals is called M-AOT (MSI-Aerosol Optical Thickness). Its main parameters are aerosol optical thickness (AOT) at 670 nm over ocean and valid land pixels and at 865 nm over ocean. Here, the algorithm and assumptions behind it are presented. Further, first examples of product parameters are given based on applying the algorithm to simulated EarthCARE test data and Moderate Resolution Imaging Spectroradiometer (MODIS) Level-1 data. Comparisons to input fields used for simulations, to the official MODIS aerosol product, to AErosol RObotic NETwork (AERONET) and to Maritime Aerosol Network (MAN) show an overall reasonable agreement. Over ocean, correlations are 0.98 (simulated scenes), 0.96 (compared to MYD04) and 0.9 (compared to MAN). Over land, correlations are 0.62 (simulated scenes), 0.87 (compared to MYD04) and 0.77 (compared to AERONET). A concluding discussion will focus on future improvements that are necessary and envisioned to enhance the product.

Direct Effects of Air Humidity on Dust Aerosol Production: Evidences for the Surprising Role of Electrostatic Forces

AbstractDust aerosols are produced by wind erosion, and it is widely accepted that dust aerosols can be produced only if the wind speed exceeds a certain threshold velocity, which is largely controlled by soil moisture content. The relative humidity (RH) in the air could affect soil moisture content, thereby impacting dust production indirectly. However, it is not clear if the RH can directly change dust aerosol production. Here we simulated dust production and show that the RH does play a direct role in affecting the production of dust aerosol in a quite complicated way, which can be explained by a hypothesis that the RH affects both the electrostatic forces and wet‐bonding forces between soil particles in opposite directions. The current formula for dust aerosol production flux does not include the direct RH effect, and this study strongly suggests that it could lead to significant errors in estimating dust production.

Harmful algal bloom aerosols and human health.

Harmful algal blooms (HABs) are increasing across many locations globally. Toxins from HABs can be incorporated into aerosols and transported inland, where subsequent exposure and inhalation can induce adverse health effects. However, the relationship between HAB aerosols and health outcomes remains unclear despite the potential for population-level exposures. In this review, we synthesized the current state of knowledge and identified evidence gaps in the relationship between HAB aerosols and human health. Aerosols from Karenia brevis, Ostreopsis sp., and cyanobacteria were linked with respiratory outcomes. However, most works did not directly measure aerosol or toxin concentrations and instead relied on proxy metrics of exposure, such as cell concentrations in nearby waterbodies. Furthermore, the number of studies with epidemiological designs was limited. Significant uncertainties remain regarding the health effects of other HAB species; threshold dose and the dose-response relationship; effects of concurrent exposures to mixtures of toxins and other aerosol sources, such as microplastics and metals; the impact of long-term exposures; and disparities in exposures and associated health effects across potentially vulnerable subpopulations. Additional studies employing multifaceted exposure assessment methods and leveraging large health databases could address such gaps and improve our understanding of the public health burden of HABs.

An algorithm for retrieving aerosol optical depth from Landsat 8 Operational Land Imager in Vietnam

High-resolution aerosol products offer advantages over lower spatial-resolution products for monitoring pollution in urban areas and industrial zones. Therefore, in this study we develop a Landsat 8 algorithm to retrieve aerosol optical depth (AOD) based on the MODIS Dark Target (DT) algorithm. This algorithm uses the direct surface reflectance of Landsat 8 to build a surface reflectance relationship between the visible (BLUE, RED) and short-wave infrared bands (SWIR2). AOD data from AERONET stations in the study area and AOD data from MODIS 3 km were used for validation of the estimated Landsat 8 AOD. The estimated AOD was highly correlated at most AERONET AOD, with =0.98, (RMSE = 0.3), except Bac Lieu, but only had a moderate correlation with MODIS AOD which was attributed to the difference in data retrieval time and associated changes in climate conditions. This is the first high-resolution AOD retrieval in Vietnam, leading to more practical applications for air quality monitoring.

Measurements of Atmosphere-Biosphere Exchange of Oxidized Nitrogen and Implications for the Chemistry of Atmospheric NOx.

ConspectusThe atmosphere-biosphere exchange of nitrogen oxides plays a key role in determining the composition of reactive nitrogen in terrestrial vegetated environments. The emission of nitric oxide (NO) from soils is an important atmospheric source of reactive nitrogen. NO is rapidly interconverted with NO2, making up the chemical family NOx (NOx ≡ NO2 + NO). NOx further reacts with the oxidation products of volatile organic compounds (VOCs) to form the functionalized nitrogen oxide groups acyl peroxynitrates (APNs = R(O)O2NO2) and alkyl nitrates (ANs = RONO2). Both canopy-level field measurements and laboratory studies suggest that the absorption of nitrogen dioxide NO2 and APNs by vegetation is a significant sink of atmospheric NOx, removing a large fraction of global soil-emitted NOx and providing key control on the amounts and lifetimes of NOx and reactive nitrogen in the atmosphere. Nitrogen oxides influence the production of surface O3 and secondary aerosols. The balance of the emission and uptake of nitrogen oxides thus provides a mechanism for the regulation of regional air quality. The biosphere, via this biogeochemical cycling of nitrogen oxides, is becoming an increasingly important determining factor for airborne pollutants as much of the world continues to reduce the amount of combustion-related nitrogen oxide emissions. Understanding the function of the biosphere as a source and sink of reactive nitrogen is therefore ever more critical in evaluating the effects of future and current emissions of nitrogen oxides on human and ecosystem health.Laboratory measurements of the foliar deposition of NO2 and other reactive nitrogen species suggest that there is a substantial diversity of uptake rates under varying environmental conditions and for different species of vegetation that is not currently reflected in the widely utilized chemical transport models. Our branch chamber measurements on a wide variety of North American tree species highlight the variability in the rates of both photosynthesis and nitrogen oxide deposition among several different nitrogen oxide compounds. Box-modeling and satellite measurement approaches demonstrate how disparities between our understanding of nitrogen oxide foliar exchange in the laboratory and what is represented in models can lead to misrepresentations of the net ecosystem exchange of nitrogen. This has important implications for assumptions of in-canopy chemistry, soil emissions of NO, canopy reductions of NOx, lifetimes of trace gases, and the impact of the biosphere on air quality.

Relationship Between the Aerosol Loadings Over the Bay of Bengal and the Arabian Sea in the Early Summer and Asian Monsoon Rainfall Anomalies, and the Role of SST Anomalies in the Indian Ocean

AbstractTwo relatively long‐term satellite aerosol products during 1983–2020 and 2000–2020 are employed to investigate interannual relationships between anomalous aerosol loadings over the Bay of Bengal (BoB) and Arabian Sea (AS) in the early summer and Asian monsoon rainfall anomalies. It is shown that increased aerosol loading (IAL) over the BoB is primarily attributed to an intensified upstream aerosol transport by anomalous subtropical westerly winds and coincides with local sea surface temperature (SST) cooling due to intensified prevailing wind and the aerosol dimming effect, and vice versa. A deficient rainfall in India tends to concur with a BoB IAL while excessive rainfall with an AS IAL in May and June. In June, a BoB IAL coincides with significantly deficient rainfall in the southwestern China‐Huaihe River Basin primarily linked to an anomalous cyclone off the coast of Southeast China. Meanwhile a related overturning of Walker Circulation is identified to be driven by the contrast of anomalous convective activity between the southeastern Indian‐BoB and the South China Sea‐Philippine Sea. An AS IAL is associated with air warming in North India due to an elevated aerosol semi‐direct effect and remote forcing that reinforces the meridional air temperature gradient. The IAL over the respective BoB and AS in June are both preceded by cold SST anomalies in the western Indian Ocean that can be traced back to the preceding winter, but the corresponding atmospheric circulations driving aerosol‐monsoon interactions differ distinctly. The above aerosol‐monsoon relationships are sustained primarily during 2000–2020 and vague during 1983–2020.

A new oxidation flow reactor for the measurements of secondary aerosol formation: Characterisation and a case study

Oxidation flow reactors (OFRs) have been extensively used to investigate secondary aerosol formation of the ambient air or emission sources such as biomass burning or vehicular emissions, and they can provide useful information on the mechanisms of secondary aerosol formation. Here we present the design and characteristics of a newly developed OFR, named the Rapid Aerosol Ageing Device (RAAD). The RAAD was specially designed to provide time-resolved and fast-response chemical evolution of aged aerosols and can be applied to investigate how oxidative stress levels change upon ageing. The characterisation experiments included optimisation of the flow rate, residence time distributions for gas and particles, transmission efficiencies of particles, OH exposures with varying O3 concentrations and relative humidity conditions. Results show that the RAAD has near-laminar flow conditions at a total flow rate of 45 slpm with a low surface-area-to-volume ratio of 26.52 m-1. Wall losses for particles with mobility diameters greater than 40 nm are negligible, and narrow residence time distributions of gas and particles were observed. These features allow a better response to the ageing of rapid-changing emission sources, and measurements can be taken directly for instruments demanding high flow rates without diluting the samples. Additionally, the performance of the RAAD was further evaluated by measuring the secondary aerosol formation of biomass burning emissions. The organic aerosol enhancement ratios were comparable with other ageing studies, with an average value of 1.31 ± 0.05. In addition, the absorption Ångström exponent (AAE) value decreased from 1.7 ± 0.05 (primary emissions) to 1.4 ± 0.06 upon ageing. Overall, the RAAD is suitable for studying the formation mechanisms of photochemically aged aerosols from emission sources, and future work will aim to provide more details on the secondary aerosol production from ambient air.

Analysis and Validation of the Aerosol Optical Depth of MODIS Products in Gansu Province, Northwest China

The accurate determination of aerosol optical depth (AOD) is of great importance for climate change research and environmental monitoring. To understand the applicability of the MODIS aerosol product inversion algorithm in Gansu Province, this work uses ground-based solar photometer AOD observation data to validate the MODIS C6 version of the AOD product. Additionally, the retrieval accuracy of MODIS C6 Deep Blue (DB) algorithm AOD products and Deep Blue and Dark Target Fusion (DB–DT combined) algorithm AOD products for Gansu Province when setting different spatial sampling windows is compared and analyzed. Meanwhile, the monitoring effects of these two AOD algorithms in typical polluted atmospheric conditions in Gansu Province are compared. The results show that (1) the correlation between the MODIS AOD products of the two algorithms and the ground-based observation data decreases with an increasing spatial sampling window size. When the spatial sampling window of the two algorithms is set at 30 km × 30 km, it is more representative of the AOD value in Gansu Province, thus reflecting local characteristics. (2) When the spatial sampling window is set at 30 km × 30 km, the inversion effect of the DB algorithm AOD is better than that of the DB–DT combined algorithm AOD on different underlying surfaces. (3) The seasonal variability in the inversion accuracy of the DB algorithm AOD is less than that of the DB–DT combined algorithm, and it has inversion advantages in spring, autumn and winter, while the DB–DT combined algorithm outperforms the DB algorithm only in winter. The inversion effect of the two algorithms on AOD is influenced by the spatial sampling window setting. (4) Both the DB algorithm AOD and the DB–DT combined algorithm AOD can monitor the distribution of AOD in the central and western regions of Gansu, especially for high values of AOD under polluted atmospheric conditions, which represents a good monitoring effect. However, the two algorithms perform poorly in monitoring the southeast region of Gansu, while there is a discontinuous AOD distribution in the northwest region of Gansu. Overall, the MODIS DB algorithm AOD product has higher applicability in Gansu Province. This work provides a good reference for local air pollution and climate prediction.

Performance evaluation of MODIS and VIIRS satellite AOD products over the Indian subcontinent

In the present study, the first systematic performance evaluation of aerosol optical depth (AOD) products retrieved using two satellite sensors i.e., Visible Infrared Imaging Radiometer Suite (VIIRS) and Aqua-Moderate-Resolution Imaging Spectroradiometer (MODIS) is carried out over India. We have used ground-based AOD from AERONET at 550 nm wavelength for inter-comparison with MODIS Aqua version C6.1 (C061) Deep Blue (DB) aerosol product and VIIRS/SNPP collection version 1.1 (V1.1) DB aerosol product over the time span of 7-year (2014–2020) observation periods. For validation, the average value of satellite pixels falling within the box of 50 Km x 50 Km keeping the AERONET station at the center is retrieved. The average daily data from the AERONET sun photometer (2014–2019) were obtained within ±15 min of satellite overpass time. Statistical parameters like correlation coefficient (R), RMSE, MAE, and RMB were calculated. The uncertainty of satellite AOD is evaluated using an envelope of Expected Error (EE = ±0.05 + 0.15 AOD for land). Statistical analysis shows that the MODIS AOD product outperforms VIIRS-retrieved AOD. The AOD retrieved from both sensors yields a high correlation (0.86—Jaipur, 0.79—Kanpur, 0.84—Gandhi College, and 0.74—Pune for MODIS and 0.75—Jaipur, 0.77—Kanpur, 0.49—Gandhi College, and 0.86—Pune for VIIRS) and low MAE (0.12—Jaipur, 0.20—Kanpur, 0.15—Gandhi College, and 0.09—Pune for MODIS and 0.13—Jaipur, 0.13—Kanpur, 0.26—Gandhi College, and 0.10—Pune for VIIRS). Other statistical measures such as RMSE, RMB, and P also suggest similar performance. More than 66% of the total data fall within the range of EE for both the satellite products at each station. Spatial comparison exhibits the same AOD pattern seasonally as well as annually having a minimum bias from −0.3 to +0.3 between MODIS and VIIRS. Slight underestimation and overestimation are observed in all the stations by MODIS, whereas VIIRS continuously underestimates AOD with increase in optical depth, suggesting improvements in the aerosol model and surface reflection in retrieval. Overall, the comparison of ground AERONET AOD reveals better accuracy of MODIS AOD with that of VIIRS satellite datasets over India.