Providing reliable observations of aerosol particles' absorption properties at spatial and temporal resolutions suited to climate models is of utter importance to better understand the effects that ...atmospheric particles have on climate. Nowadays, one of the instruments most widely used in international monitoring networks for in situ surface measurements of light absorption properties of atmospheric aerosol particles is the multi-wavelength dual-spot Aethalometer, AE33. The AE33 derives the absorption coefficients of aerosol particles at seven different wavelengths from the measurements of the optical attenuation of light through a filter where particles are continuously collected. An accurate determination of the absorption coefficients from the AE33 instrument relies on the quantification of the non-linear processes related to the sample collection on the filter. The multiple-scattering correction factor (C), which depends on the filter tape used and on the optical properties of the collected particles, is the parameter with both the greatest uncertainty and the greatest impact on the absorption coefficients derived from the AE33 measurements.
La Paz and El Alto are two fast-growing, high-altitude Bolivian cities forming the second-largest metropolitan area in the country. Located between 3200 and 4050 m a.s.l. (above sea level), these ...cities are home to a burgeoning population of approximately 1.8 million residents. The air quality in this conurbation is heavily influenced by urbanization; however, there are no comprehensive studies evaluating the sources of air pollution and their health impacts. Despite their proximity, the substantial variation in altitude, topography, and socioeconomic activities between La Paz and El
Alto result in distinct sources, dynamics, and transport of particulate matter (PM). In this investigation, PM10 samples were collected at two
urban background stations located in La Paz and El Alto between April 2016
and June 2017. The samples were later analyzed for a wide range of chemical
species including numerous source tracers (OC, EC, water-soluble ions, sugar anhydrides, sugar alcohols, trace metals, and molecular organic species). The United States Environmental Protection Agency (U.S. EPA) Positive Matrix Factorization (PMF v.5.0) receptor model was employed for the source apportionment of PM10. This is one of the first source apportionment studies in South America that incorporates an extensive suite of organic markers, including levoglucosan, polycyclic aromatic hydrocarbons (PAHs), hopanes, and alkanes, alongside inorganic species. The multisite PMF resolved 11 main sources of PM. The largest annual contribution to PM10 came from the following two major sources: the ensemble of the four vehicular emissions sources (exhaust and non-exhaust), accountable for 35 % and 25 % of the measured PM in La Paz and El Alto, respectively; and dust, which contributed 20 % and 32 % to the total PM mass. Secondary aerosols accounted for 22 % (24 %) in La Paz (El Alto). Agricultural smoke resulting from biomass burning in the Bolivian lowlands
and neighboring countries contributed to 9 % (8 %) of the total
PM10 mass annually, increasing to 17 % (13 %) between August–October. Primary biogenic emissions were responsible for 13 %
(7 %) of the measured PM10 mass. Additionally, a profile associated
with open waste burning occurring from May to August was identified. Although this source contributed only to 2 % (5 %) of the total PM10 mass, it constitutes the second largest source of PAHs, which are compounds potentially hazardous to human health. Our analysis additionally resolved two different traffic-related factors, a lubricant source (not
frequently identified), and a non-exhaust emissions source. Overall, this
study demonstrates that PM10 concentrations in La Paz and El Alto
region are predominantly influenced by a limited number of local sources. In conclusion, to improve air quality in both cities, efforts should primarily focus on addressing dust, traffic emissions, open waste burning, and biomass burning.
At city level, personal monitoring is the best way to assess people's exposure. However, it is usually estimated from a few monitoring stations. Our aim was to determine the exposure to black carbon ...(BC) and BC dose for 45 schoolchildren with portable microaethalometers and to evaluate the relationship between personal monitoring and fixed stations at schools (indoor and outdoor) and in an urban background (UB) site. Personal BC concentra‐tions were 20% higher than in fixed stations at schools. Linear mixed‐effect models showed low R2 between personal measurements and fixed stations at schools (R2 ≤ 0.28), increasing to R2 ≥ 0.70 if considering only periods when children were at schools. For the UB station, the respective R2 were 0.18 and 0.45, indicating the importance of the distance to the monitoring station when assessing exposure. During the warm season, the fixed stations agreed better with personal measurements than during the cold one. Children spent 6% of their time on commuting but received 20% of their daily BC dose, due to co‐occurrence with road traffic rush hours and the close proximity to the source. Children received 37% of their daily‐integrated BC dose at school. Indoor environments (classroom and home) were responsible for the 56% BC dose.
New aerosol particle formation (NPF) events play a significant role in altering aerosol concentrations and dispersion within the atmosphere, making them vital for both climate and air quality ...research. The primary objective of investigating NPF events is to precisely determine their occurrence dates. In this study, we introduced the ConvNeXt model for the first time to identify NPF events, and compared its performance with two other deep learning models, EfficientNet and Swin Transformer. Our main aim was to automate an objective identification and classification of NPF events accurately. All three models employed transfer learning to effectively capture critical features associated with NPF. Our results demonstrated that the ConvNeXt model significantly outperformed the other models, achieving an impressive accuracy rate of 95.3% on event days, surpassing EfficientNet (92.8%) and Swin Transformer (94.9%). Furthermore, we performed tests using different ConvNeXt variants (ConvNeXt-T/S/B/L/XL) and different pre-training weights, revealing that different configurations of ConvNeXt models exhibited improved NPF event recognition capabilities. Finally, we conducted generalizability experiments using the ConvNeXt-XL model, achieving the highest accuracy of 96.4% on event days. This study not only underscores the recognition prowess of ConvNeXt models but also highlights their practical utility in accurately detecting NPF events in real-world scenarios. This contribution aids in advancing our comprehension of aerosol dynamics in atmospheric environments, providing valuable insights for climate and air quality research.
•Employed ConvNeXt model, used transfer learning to identify NPF events.•Comparative analysis showed ConvNeXt's outstanding 95.3% accuracy.•Tests with different ConvNeXt variants demonstrated enhanced capabilities.•ConvNeXt-XL excelled, achieving 96.4% accuracy in generalization experiments.
Accurate measurements of the horizontal and vertical distribution of atmospheric aerosol particle optical properties are key for a better
understanding of their impact on the climate. Here we present ...the results of a measurement campaign based on instrumented flights over north-eastern Spain. We measured vertical profiles of size-segregated atmospheric particulate matter (PM) mass concentrations and multi-wavelength scattering and absorption coefficients in the western Mediterranean basin (WMB). The campaign took place during typical summer conditions, characterized by the development of a vertical multi-layer structure, under both summer regional pollution episodes (REGs) and Saharan dust events (SDEs). REG patterns in the region form under high insolation and scarce precipitation in summer, favouring layering of highly aged fine-PM strata in the lower few kma.s.l. The REG scenario prevailed during the entire measurement campaign. Additionally, African dust outbreaks and plumes from northern African wildfires influenced the study area. The vertical profiles of climate-relevant intensive optical parameters such as single-scattering albedo (SSA); the asymmetry parameter (g); scattering, absorption and SSA Ångström exponents (SAE, AAE and SSAAE); and PM mass scattering and absorption cross sections (MSC and MAC) were derived from the measurements. Moreover, we compared the aircraft measurements with those performed at two GAW–ACTRIS (Global Atmosphere Watch–Aerosol, Clouds and Trace Gases) surface measurement stations located in north-eastern Spain, namely Montseny (MSY; regional background) and Montsec d'Ares (MSA; remote site). Airborne in situ measurements and ceilometer ground-based remote measurements identified aerosol air masses at altitudes up to more than
3.5 kma.s.l. The vertical profiles of the optical properties markedly changed according to the prevailing atmospheric scenarios. During
SDE the SAE was low along the profiles, reaching values < 1.0 in the dust layers. Correspondingly, SSAAE was negative, and AAE reached values up
to 2.0–2.5, as a consequence of the UV absorption increased by the presence of the coarse dust particles. During REG, the SAE increased to > 2.0, and the asymmetry parameter g was rather low (0.5–0.6) due to the prevalence of fine PM, which was characterized by an AAE close to 1.0, suggesting a fossil fuel combustion origin. During REG, some of the layers featured larger AAE (> 1.5), relatively low SSA at 525 nm (< 0.85) and high MSC (> 9 m2 g−1) and were associated with the influence of PM from wildfires. Overall, the SSA and MSC near the ground ranged around 0.85 and 3 m2 g−1, respectively, and increased at higher altitudes, reaching values above 0.95 and up to 9 m2 g−1. The PM, MSC and MAC were on average larger during REG compared to SDE due to the larger scattering and absorption efficiency of fine PM compared with dust. The SSA and MSC had quite similar vertical profiles and often both increased with height indicating the progressive shift toward PM with a larger scattering efficiency with altitude. This study contributes to our understanding of regional-aerosol vertical distribution and optical properties in the WMB, and the results will be useful for improving future climate projections and remote sensing or satellite retrieval algorithms.
Given the need for accurate knowledge of aerosol
microphysical and optical properties with height resolution, various
algorithms combining vertically resolved and column-integrated aerosol
...information have been developed in the last years. Here we present new
results of vertically resolved extensive aerosol optical properties
(backscattering, scattering and extinction) and volume concentrations
retrieved with the GRASP (Generalized Retrieval of Aerosol and Surface
Properties) algorithm over a 3-year period. The range-corrected signal (RCS)
at 1064 nm measured with a ceilometer and the aerosol optical depth (AOD)
and sky radiances from a sun/sky photometer have been used as input for this
algorithm. We perform a detailed evaluation of GRASP retrievals with
simultaneous in situ measurements performed at the same height, at the
Montsec mountaintop observatory (MSA) in the Pre-Pyrenees (northeastern
Spain). This is the first long-term evaluation of various outputs of this
algorithm; previous evaluations focused only on the study of aerosol volume
concentration for short-term periods. In general, our results show good
agreement between techniques although GRASP inversions yield higher values
than those measured in situ. The statistical analysis of the extinction
coefficient vertical profiles shows a clear seasonality as well as
significant differences depending on the air mass origin. The observed
seasonal cycle is mainly modulated by a higher development of the
atmospheric boundary layer (ABL) during warm months, which favors the
transport of pollutants to MSA, and higher influence of regional and
North African episodes. On the other hand, in winter, MSA is frequently
influenced by free-troposphere conditions and venting periods and therefore
lower extinction coefficients that markedly decrease with height. This study
shows the potentiality of implementing GRASP in ceilometer and lidar
networks for obtaining aerosol optical properties and volume concentrations
at multiple sites, which will definitely contribute to enhancing the
representativeness of the aerosol vertical distribution as well as to providing
useful information for satellite and global model evaluation.
Here we report results of a detailed analysis of the urban and non-urban
contributions to particulate matter (PM) concentrations and source contributions in five European
cities, namely Schiedam (the ...Netherlands, NL), Lens (France, FR), Leipzig
(Germany, DE), Zurich (Switzerland, CH) and Barcelona (Spain, ES). PM
chemically speciated data from 12 European paired monitoring sites (one
traffic, five urban, five regional and one continental background) were analysed by
positive matrix factorisation (PMF) and Lenschow's approach to assign
measured PM and source contributions to the different spatial levels. Five
common sources were obtained at the 12 sites: sulfate-rich (SSA) and nitrate-rich (NSA) aerosols,
road traffic (RT), mineral matter (MM), and aged sea salt (SS). These sources explained from 55 % to 88 % of PM
mass at urban low-traffic-impact sites (UB) depending on the country. Three
additional common sources were identified at a subset of sites/countries,
namely biomass burning (BB) (FR, CH and DE), explaining an additional 9 %–13 % of PM
mass, and residual oil combustion (V–Ni) and primary industrial (IND) (NL and ES), together explaining an additional
11 %–15 % of PM mass. In all countries, the majority of PM measured at UB
sites was of a regional+continental (R+C) nature (64 %–74 %). The R+C PM
increments due to anthropogenic emissions in DE, NL, CH, ES and FR
represented around 66 %, 62 %, 52 %, 32 % and 23 %, respectively,
of UB PM mass. Overall, the R+C PM increments due to natural and
anthropogenic sources showed opposite seasonal profiles with the former
increasing in summer and the latter increasing in winter, even if exceptions
were observed. In ES, the anthropogenic R+C PM increment was higher in
summer due to high contributions from regional SSA and V–Ni sources, both
being mostly related to maritime shipping emissions at the Spanish sites.
Conversely, in the other countries, higher anthropogenic R+C PM increments
in winter were mostly due to high contributions from NSA and BB regional
sources during the cold season. On annual average, the sources showing
higher R+C increments were SSA (77 %–91 % of SSA source contribution at the
urban level), NSA (51 %–94 %), MM (58 %–80 %), BB (42 %–78 %) and IND (91 %
in NL). Other sources showing high R+C increments were photochemistry and coal combustion (97 %–99 %;
identified only in DE). The highest regional SSA increment was observed in
ES, especially in summer, and was related to ship emissions, enhanced
photochemistry and peculiar meteorological patterns of the Western
Mediterranean. The highest R+C and urban NSA increments were observed in
NL and associated with high availability of precursors such as NOx and
NH3. Conversely, on average, the sources showing higher local
increments were RT (62 %–90 % at all sites) and V–Ni (65 %–80 % in ES and
NL). The relationship between SSA and V–Ni indicated that the contribution
of ship emissions to the local sulfate concentrations in NL has strongly
decreased since 2007 thanks to the shift from high-sulfur- to low-sulfur-content fuel used by ships. An improvement of air quality in the five cities
included here could be achieved by further reducing local (urban) emissions
of PM, NOx and NH3 (from both traffic and non-traffic sources) but
also SO2 and PM (from maritime ships and ports) and giving high
relevance to non-urban contributions by further reducing emissions of
SO2 (maritime shipping) and NH3 (agriculture) and those from
industry, regional BB sources and coal combustion.
In order to assess the evolution of aerosol parameters affecting climate change, a long-term trend analysis of aerosol optical properties was performed on time series from 52 stations situated across ...five continents. The time series of measured scattering, backscattering and absorption coefficients as well as the derived single scattering albedo, backscattering fraction, scattering and absorption Ångström exponents covered at least 10 years and up to 40 years for some stations. The non-parametric seasonal Mann–Kendall (MK) statistical test associated with several pre-whitening methods and with Sen's slope was used as the main trend analysis method. Comparisons with general least mean square associated with autoregressive bootstrap (GLS/ARB) and with standard least mean square analysis (LMS) enabled confirmation of the detected MK statistically significant trends and the assessment of advantages and limitations of each method. Currently, scattering and backscattering coefficient trends are mostly decreasing in Europe and North America and are not statistically significant in Asia, while polar stations exhibit a mix of increasing and decreasing trends. A few increasing trends are also found at some stations in North America and Australia. Absorption coefficient time series also exhibit primarily decreasing trends. For single scattering albedo, 52 % of the sites exhibit statistically significant positive trends, mostly in Asia, eastern/northern Europe and the Arctic, 22 % of sites exhibit statistically significant negative trends, mostly in central Europe and central North America, while the remaining 26 % of sites have trends which are not statistically significant. In addition to evaluating trends for the overall time series, the evolution of the trends in sequential 10-year segments was also analyzed. For scattering and backscattering, statistically significant increasing 10-year trends are primarily found for earlier periods (10-year trends ending in 2010–2015) for polar stations and Mauna Loa. For most of the stations, the present-day statistically significant decreasing 10-year trends of the single scattering albedo were preceded by not statistically significant and statistically significant increasing 10-year trends. The effect of air pollution abatement policies in continental North America is very obvious in the 10-year trends of the scattering coefficient – there is a shift to statistically significant negative trends in 2009–2012 for all stations in the eastern and central USA. This long-term trend analysis of aerosol radiative properties with a broad spatial coverage provides insight into potential aerosol effects on climate changes.
This study documents and analyses a 4-year continuous record of aerosol optical properties measured at the Global Atmosphere Watch (GAW) station of Chacaltaya (CHC; 5240 m a.s.l.), in Bolivia. ...Records of particle light scattering and particle light absorption coefficients are used to investigate how the high Andean Cordillera is affected by both long-range transport and by the fast-growing agglomeration of La Paz–El Alto, located approximately 20 km away and 1.5 km below the sampling site. The extended multi-year record allows us to study the properties of aerosol particles for different air mass types, during wet and dry seasons, also covering periods when the site was affected by biomass burning in the Bolivian lowlands and the Amazon Basin. The absorption, scattering, and extinction coefficients (median annual values of 0.74, 12.14, and 12.96 Mm−1 respectively) show a clear seasonal variation with low values during the wet season (0.57, 7.94, and 8.68 Mm−1 respectively) and higher values during the dry season (0.80, 11.23, and 14.51 Mm−1 respectively). The record is driven by variability at both seasonal and diurnal scales. At a diurnal scale, all records of intensive and extensive aerosol properties show a pronounced variation (daytime maximum, night-time minimum), as a result of the dynamic and convective effects. The particle light absorption, scattering, and extinction coefficients are on average 1.94, 1.49, and 1.55 times higher respectively in the turbulent thermally driven conditions than the more stable conditions, due to more efficient transport from the boundary layer. Retrieved intensive optical properties are significantly different from one season to the other, reflecting the changing aerosol emission sources of aerosol at a larger scale. Using the wavelength dependence of aerosol particle optical properties, we discriminated between contributions from natural (mainly mineral dust) and anthropogenic (mainly biomass burning and urban transport or industries) emissions according to seasons and local circulation. The main sources influencing measurements at CHC are from the urban area of La Paz–El Alto in the Altiplano and from regional biomass burning in the Amazon Basin. Results show a 28 % to 80 % increase in the extinction coefficients during the biomass burning season with respect to the dry season, which is observed in both tropospheric dynamic conditions. From this analysis, long-term observations at CHC provide the first direct evidence of the impact of biomass burning emissions of the Amazon Basin and urban emissions from the La Paz area on atmospheric optical properties at a remote site all the way to the free troposphere.
Perivascular spaces (PVSs) surrounding the walls of arteries, arterioles, and venules are a common finding in brain imaging. Even if they do not directly communicate with subarachnoid spaces, there ...are some cases in which subarachnoid hemorrhage (SAH) and intracerebral hematomas extend to the PVSs by leakage of the leptomeninges. In this report, we present a case of enlargement and bleeding of PVSs in the midbrain of a young woman with head trauma, without evident SAH or intracerebral hematomas.
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