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Recent years have seen an increase in the use of wood for energy production of over 30 %, and this trend is expected to continue due to the current energy crisis and geopolitical instability. At present, residential wood burning (RWB) is one of the most important sources of organic aerosols (OAs) and black carbon (BC), posing a significant risk to air quality and health. Simultaneously, as a substantial aerosol source, RWB also holds relevance in the context of aerosol radiative effects and climate. While BC is recognized for its large light absorption cross-section, the role of OAs in light absorption is still under evaluation due to their heterogeneous composition and source-dependent optical properties. Existing studies that characterize wood-burning aerosol emissions in Europe primarily concentrate on urban and background sites and focus on BC properties. Despite the significant RWB emissions in rural areas, these locations have received comparatively less attention. The present scenario underscores the imperative for an improved understanding of RWB pollution, aerosol optical properties, and their subsequent connection to climate impacts, particularly in rural areas. We have characterized atmospheric aerosol particles from a central European rural site during wintertime in the village of Retje in Loški Potok, Slovenia, from 1 December 2017 to 7 March 2018. The village experienced extremely high aerosol concentrations produced by RWB and near-ground temperature inversion. The isolated location of the site and the substantial local emissions made it an ideal laboratory-like place for characterizing RWB aerosols with low influence from non-RWB sources under ambient conditions. The mean mass concentrations of OA and BC were 35 µg m−3 (max⁡=270 µg m−3) and 3.1 µg m−3 (max⁡=24 µg m−3), respectively. The mean total particle number concentration (10–600 nm) was 9.9×103 particles cm−3 (max⁡=59×103 particles cm−3). The mean total light absorption coefficients at 370 and 880 nm measured by an AE33 Aethalometer were 120 and 22 Mm−1 and had maximum values of 1100 and 180 Mm−1, respectively. The aerosol concentrations and absorption coefficients measured during the campaign in Loški Potok were significantly larger than reported values for several urban areas in the region with larger populations and a larger extent of aerosol sources. Here, considerable contributions from brown carbon (BrC) to the total light absorption were identified, reaching up to 60 % and 48 % in the near-UV (370 nm) and blue (470 nm) wavelengths. These contributions are up to 3 times higher than values reported for other sites impacted by wood-burning emissions. The calculated mass absorption cross-section and the absorption Ångström exponent for RWB OA were MACOA,370nm=2.4 m2 g−1, and AAEBrC,370-590nm=3.9, respectively. Simple-forcing-efficiency (SFE) calculations were performed as a sensitivity analysis to evaluate the climate impact of the RWB aerosols produced at the study site by integrating the optical properties measured during the campaign. The SFE results show a considerable forcing capacity from the local RWB aerosols, with a high sensitivity to OA absorption properties and a more substantial impact over bright surfaces like snow, typical during the coldest season with higher OA emissions from RWB. Our study's results are highly significant regarding air pollution, optical properties, and climate impact. The findings suggest that there may be an underestimation of RWB emissions in rural Europe and that further investigation is necessary.

The geographical origin and source apportionment of submicron carbonaceous aerosols (organic aerosols, OAs, and black carbon, BC) have been investigated here for the first time, deploying high time-resolution measurements at an urban background site of Nicosia, the capital city of Cyprus, in the eastern Mediterranean. This study covers a half-year period, encompassing both the cold and warm periods with continuous observations of the physical and chemical properties of PM1 performed with an Aerosol Chemical Speciation Monitor (ACSM), an aethalometer, accompanied by a suite of various ancillary offline and online measurements. Carbonaceous aerosols were dominant during both seasons (cold and warm periods), with a contribution of 57 % and 48 % to PM1, respectively, and exhibited recurrent intense nighttime peaks (> 20–30 µg m−3) during the cold period, associated with local domestic heating. The findings of this study show that high concentrations of sulfate (close to 3 µg m−3) were continuously recorded, standing among the highest ever reported for Europe and originating from the Middle East region. Source apportionment of the OA and BC fractions was performed using the positive matrix factorization (PMF) approach and the combination of two models (aethalometer model and multilinear regression), respectively. Our study revealed elevated hydrocarbon-like organic aerosol (HOA) concentrations in Nicosia (among the highest reported for a European urban background site), originating from a mixture of local and regional fossil fuel combustion sources. Although air masses from the Middle East had a low occurrence and were observed mostly during the cold period, they were shown to strongly affect the mean concentrations levels of BC and OA in Nicosia during both seasons. Overall, the present study brings to our attention the need to further characterize primary and secondary carbonaceous aerosols in the Middle East, an undersampled region characterized by continuously increasing fossil fuel (oil and gas) emissions and extreme environmental conditions, which can contribute to photochemical ageing.

Black carbon (BC) aerosol typically has two major sources in the urban environment: traffic and domestic biomass burning, which has a significant contribution to urban air pollution during the heating season. Traffic emissions have been widely studied by both laboratory experiments (individual vehicle emission) and real-world measurement campaigns (fleet emission). However, emission information from biomass burning is limited, especially an insufficiency of experimental results from real-world studies. In this work, the black carbon burden in the urban atmosphere was apportioned to fossil fuel (FF) and biomass burning (BB) related components using the Aethalometer source apportionment model. Applying the BC source apportionment information, the combustion-related CO2 was apportioned by multilinear regression analysis, supposing that both CO2 components should be correlated with their corresponding BC component. The combination of the Aethalometer model with the multilinear regression analysis (AM-MLR) provided the source-specific emission ratios (ERs) as the slopes of the corresponding BC–CO2 regressions. Based on the ER values, the source-specific emission factors (EFs) were determined using the carbon content of the corresponding fuel. The analysis was carried out on a 3-month-long BC and CO2 dataset collected at three monitoring locations in Ljubljana, Slovenia, between December 2019 and March 2020. The measured mean site-specific concentration values were in the 3560–4830 ng m−3 and 458–472 ppm ranges for BC and CO2, respectively. The determined average EFs for BC were 0.39 and 0.16 g(kg fuel)−1 for traffic and biomass burning, respectively. It was also concluded that the traffic-related BC component dominates the black carbon concentration (55 %–64 % depending on the location), while heating has the major share in the combustion-related CO2 (53 %–62 % depending on the location). The method gave essential information on the source-specific emission factors of BC and CO2, enabling better characterization of urban anthropogenic emissions and the respective measures that may change the anthropogenic emission fingerprint.

Black carbon (BC) is recognized as the most important warming agent among atmospheric aerosol particles. The absorption efficiency of pure BC is rather well-known, nevertheless the mixing of BC with other aerosol particles can enhance the BC light absorption efficiency, thus directly affecting Earth's radiative balance. The effects on climate of the BC absorption enhancement due to the mixing with these aerosols are not yet well constrained because these effects depend on the availability of material for mixing with BC, thus creating regional variations. Here we present the mass absorption cross-section (MAC) and absorption enhancement of BC particles (Eabs), at different wavelengths (from 370 to 880 nm for online measurements and at 637 nm for offline measurements) measured at two sites in the western Mediterranean, namely Barcelona (BCN; urban background) and Montseny (MSY; regional background). The Eabs values ranged between 1.24 and 1.51 at the urban station, depending on the season and wavelength used as well as on the pure BC MAC used as a reference. The largest contribution to Eabs was due to the internal mixing of BC particles with other aerosol compounds, on average between a 91 % and a 100 % at 370 and 880 nm, respectively. Additionally, 14.5 % and 4.6 % of the total enhancement at the short ultraviolet (UV) wavelength (370 nm) was due to externally mixed brown carbon (BrC) particles during the cold and the warm period, respectively. On average, at the MSY station, a higher Eabs value was observed (1.83 at 637 nm) compared to BCN (1.37 at 637 nm), which was associated with the higher fraction of organic aerosols (OA) available for BC coating at the regional station, as denoted by the higher organic carbon to elemental carbon (OC:EC) ratio observed at MSY compared to BCN. At both BCN and MSY, Eabs showed an exponential increase with the amount of non-refractory (NR) material available for coating (RNR-PM). The Eabs at 637 nm at the MSY regional station reached values up to 3 during episodes with high RNR-PM, whereas in BCN, Eabs kept values lower than 2 due to the lower relative amount of coating materials measured at BCN compared to MSY. The main sources of OA influencing Eabs throughout the year were hydrocarbon OA (HOA) and cooking-related OA (COA), i.e. primary OA (POA) from traffic and cooking emissions, respectively, at both 370 and 880 nm. At the short UV wavelength (370 nm), a strong contribution to Eabs from biomass burning OA (BBOA) and less oxidized oxygenated OA (LO-OOA) sources was observed in the colder period. Moreover, we found an increase of Eabs with the ageing state of the particles, especially during the colder period. This increase of Eabs with particle ageing was associated with a larger relative amount of secondary OA (SOA) compared to POA. The availability of a long dataset at both stations from offline measurements enabled a decade-long trend analysis of Eabs at 637 nm, that showed statistically significant (s.s.) positive trends of Eabs during the warmer months at the MSY station. This s.s. positive trend in MSY mirrored the observed increase of the OC:EC ratio over time. Moreover, in BCN during the COVID-19 lockdown period in spring 2020 we observed a sharp increase of Eabs due to the observed sharp increase of the OC:EC ratio. Our results show similar values of Eabs to those found in the literature for similar background stations.

Residential wood combustion is a widespread practice in Europe with a serious impact on air quality, especially in mountainous areas. While there is a significant number of studies conducted in deep urbanized valleys and basins, little is known about the air pollution processes in rural shallow hollows, where around 30 % of the people in mountainous areas across Europe live. We aim to determine the influence of ground temperature inversions on wood combustion aerosol pollution in hilly, rural areas. The study uses Retje karst hollow (Loški Potok, Slovenia) as a representative site for mountainous and hilly rural areas in central and south-eastern Europe with residential wood combustion. Sampling with a mobile monitoring platform along the hollow was performed in December 2017 and January 2018. The backpack mobile monitoring platform was used for the determination of equivalent black carbon (eBC) and particulate matter (PM) mass concentrations along the hollow. To ensure high quality of mobile measurement data, intercomparisons of mobile instruments with reference instruments were performed at two air quality stations during every run. Our study showed that aerosol pollution events in the relief depression were associated with high local emission intensities originating almost entirely from residential wood burning and shallow temperature inversions (58 m on average). The eBC and PM mass concentrations showed stronger associations with the potential temperature gradient (R2=0.8) than with any other meteorological parameters taken into account (ambient temperature, relative humidity, wind speed, wind direction, and precipitation). The strong association between the potential temperature gradient and pollutant concentrations suggests that even a small number of emission sources (total 243 households in the studied hollow) in similar hilly and mountainous rural areas with frequent temperature inversions can significantly increase the levels of eBC and PM and deteriorate local air quality. During temperature inversions the measured mean eBC and PM2.5 mass concentrations in the whole hollow were as high as 4.5±2.6 and 48.0 ± 27.7 µg m−3, respectively, which is comparable to larger European urban centres.

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. Here we present an in-depth analysis of the AE33 multiple-scattering correction factor C and its wavelength dependence for two different and widely used filter tapes, namely the old, and most referenced, TFE-coated glass, or M8020, filter tape and the currently, and most widely used, M8060 filter tape. For performing this analysis, we compared the attenuation measurements from AE33 with the absorption coefficients measured with different filter-based techniques. On-line co-located multi-angle absorption photometer (MAAP) measurements and off-line PP_UniMI polar photometer measurements were employed as reference absorption measurements for this work. To this aim, we used data from three different measurement stations located in the north-east of Spain, namely an urban background station (Barcelona, BCN), a regional background station (Montseny, MSY) and a mountaintop station (Montsec d'Ares, MSA). The median C values (at 637 nm) measured at the three stations ranged between 2.29 (at BCN and MSY, lowest 5th percentile of 1.97 and highest 95th percentile of 2.68) and 2.51 (at MSA, lowest 5th percentile of 2.06 and highest 95th percentile of 3.06). The analysis of the cross-sensitivity to scattering, for the two filter tapes considered here, revealed a large increase in the C factor when the single-scattering albedo (SSA) of the collected particles was above a given threshold, up to a 3-fold increase above the average C values. The SSA threshold appeared to be site dependent and ranged between 0.90 to 0.95 for the stations considered in the study. The results of the cross-sensitivity to scattering displayed a fitted constant multiple-scattering parameter, Cf, of 2.21 and 1.96, and a cross-sensitivity factor, ms, of 1.8 % and 3.4 % for the MSY and MSA stations, respectively, for the TFE-coated glass filter tape. For the M8060 filter tape, Cf values of 2.50, 1.96 and 1.82 and ms values of 1.6 %, 3.0 % and 4.9 % for the BCN, MSY and MSA stations, respectively, were obtained. SSA variations also influenced the spectral dependence of C, which showed an increase with wavelength when SSA was above the site-dependent threshold. Below the SSA threshold, no statistically significant dependence of C on the wavelength was observed. For the measurement stations considered here, the wavelength dependence of C was to some extent driven by the presence of dust particles during Saharan dust outbreaks that had the potential to increase the SSA above the average values. At the mountaintop station, an omission of the wavelength dependence of the C factor led to an underestimation of the absorption Ångström exponent (AAE) by up to 12 %. Differences in the absorption coefficient determined from AE33 measurements at BCN, MSY and MSA of around 35 %–40 % can be expected when using the site-dependent experimentally obtained C value instead of the nominal C value. Due to the fundamental role that the SSA of the particles collected on the filter tape has in the multiple-scattering parameter C, we present a methodology that allows the recognition of the conditions upon which the use of a constant and wavelength-independent C is feasible.

In the frame of the EMEP/ACTRIS/COLOSSAL campaign in Milan during winter 2018, equivalent black carbon measurements using the Aethalometer 31 (AE31), the Aethalometer 33 (AE33), and a Multi-Angle Absorption Photometer (MAAP) were carried out together with levoglucosan analyses on 12 h resolved PM2.5 samples collected in parallel. From AE31 and AE33 data, the loading-corrected aerosol attenuation coefficients (bATN) were calculated at seven wavelengths (λ, where λ values are 370, 470, 520, 590, 660, 880, and 950 nm). The aerosol absorption coefficient at 637 nm (babs_MAAP) was determined by MAAP measurements. Furthermore, babs was also measured at four wavelengths (405, 532, 635, 780 nm) on the 12 h resolved PM2.5 samples by a polar photometer (PP_UniMI). After comparing PP_UniMI and MAAP results, we exploited PP_UniMI data to evaluate the filter multiple-scattering enhancement parameter at different wavelengths for AE31 and AE33. We obtained instrument- and wavelength-dependent multiple-scattering enhancement parameters by linear regression of the Aethalometer bATN against the babs measured by PP_UniMI. We found significant dependence of the multiple-scattering enhancement parameter on filter material, hence on the instrument, with a difference of up to 30 % between the AE31 and the AE33 tapes. The wavelength dependence and day–night variations were small – the difference between the smallest and largest value was up to 6 %. Data from the different instruments were used as input to the so-called “Aethalometer model” for optical source apportionment, and instrument dependence of the results was investigated. Inconsistencies among the source apportionment were found fixing the AE31 and AE33 multiple-scattering enhancement parameters to their usual values. In contrast, optimised multiple-scattering enhancement parameters led to a 5 % agreement among the approaches. Also, the component apportionment “MWAA model” (Multi-Wavelength Absorption Analyzer model) was applied to the dataset. It was less sensitive to the instrument and the number of wavelengths, whereas significant differences in the determination of the absorption Ångström exponent for brown carbon were found (up to 22 %).

We experimentally quantified the impact of cloud fraction and cloud type on the heating rate (HR) of black and brown carbon (HRBC and HRBrC). In particular, we examined in more detail the cloud effect on the HR detected in a previous study (Ferrero et al., 2018). High-time-resolution measurements of the aerosol absorption coefficient at multiple wavelengths were coupled with spectral measurements of the direct, diffuse and surface reflected irradiance and with lidar–ceilometer data during a field campaign in Milan, Po Valley (Italy). The experimental set-up allowed for a direct determination of the total HR (and its speciation: HRBC and HRBrC) in all-sky conditions (from clear-sky conditions to cloudy). The highest total HR values were found in the middle of winter (1.43 ± 0.05 K d−1), and the lowest were in spring (0.54 ± 0.02 K d−1). Overall, the HRBrC accounted for 13.7 ± 0.2 % of the total HR, with the BrC being characterized by an absorption Ångström exponent (AAE) of 3.49 ± 0.01. To investigate the role of clouds, sky conditions were classified in terms of cloudiness (fraction of the sky covered by clouds: oktas) and cloud type (stratus, St; cumulus, Cu; stratocumulus, Sc; altostratus, As; altocumulus, Ac; cirrus, Ci; and cirrocumulus–cirrostratus, Cc–Cs). During the campaign, clear-sky conditions were present 23 % of the time, with the remaining time (77 %) being characterized by cloudy conditions. The average cloudiness was 3.58 ± 0.04 oktas (highest in February at 4.56 ± 0.07 oktas and lowest in November at 2.91 ± 0.06 oktas). St clouds were mostly responsible for overcast conditions (7–8 oktas, frequency of 87 % and 96 %); Sc clouds dominated the intermediate cloudiness conditions (5–6 oktas, frequency of 47 % and 66 %); and the transition from Cc–Cs to Sc determined moderate cloudiness (3–4 oktas); finally, low cloudiness (1–2 oktas) was mostly dominated by Ci and Cu (frequency of 59 % and 40 %, respectively). HR measurements showed a constant decrease with increasing cloudiness of the atmosphere, enabling us to quantify for the first time the bias (in %) of the aerosol HR introduced by the simplified assumption of clear-sky conditions in radiative-transfer model calculations. Our results showed that the HR of light-absorbing aerosol was ∼ 20 %–30 % lower in low cloudiness (1–2 oktas) and up to 80 % lower in completely overcast conditions (i.e. 7–8 oktas) compared to clear-sky ones. This means that, in the simplified assumption of clear-sky conditions, the HR of light-absorbing aerosol can be largely overestimated (by 50 % in low cloudiness, 1–2 oktas, and up to 500 % in completely overcast conditions, 7–8 oktas). The impact of different cloud types on the HR was also investigated. Cirrus clouds were found to have a modest impact, decreasing the HRBC and HRBrC by −5 % at most. Cumulus clouds decreased the HRBC and HRBrC by −31 ± 12 % and −26 ± 7 %, respectively; cirrocumulus–cirrostratus clouds decreased the HRBC and HRBrC by −60 ± 8 % and −54 ± 4 %, which was comparable to the impact of altocumulus (−60 ± 6 % and −46 ± 4 %). A higher impact on the HRBC and HRBrC suppression was found for stratocumulus (−63 ± 6 % and −58 ± 4 %, respectively) and altostratus (−78 ± 5 % and −73 ± 4 %, respectively). The highest impact was associated with stratus, suppressing the HRBC and HRBrC by −85 ± 5 % and −83 ± 3 %, respectively. The presence of clouds caused a decrease of both the HRBC and HRBrC (normalized to the absorption coefficient of the respective species) of −11.8 ± 1.2 % and −12.6 ± 1.4 % per okta. This study highlights the need to take into account the role of both cloudiness and different cloud types when estimating the HR caused by both BC and BrC and in turn decrease the uncertainties associated with the quantification of their impact on the climate.

We present a newly developed total carbon analyzer (TCA08) and a method for online speciation of carbonaceous aerosol with a high time resolution. The total carbon content is determined by flash heating of a sample collected on a quartz-fiber filter with a time base between 20 min and 24 h. The limit of detection is approximately 0.3 µg C, which corresponds to a concentration of 0.3 µg C m−3 at a sample flow rate of 16.7 L min−1 and a 1 h sampling time base. The concentration of particulate equivalent organic carbon (OC) is determined by subtracting black carbon concentration, concurrently measured optically by an Aethalometer®, from the total carbon concentration measured by the TCA08. The combination of the TCA08 and Aethalometer (AE33) is an easy-to-deploy and low-maintenance continuous measurement technique for the high-time-resolution determination of equivalent organic and elemental carbon (EC) in different particulate matter size fractions, which avoids pyrolytic correction and the need for high-purity compressed gases. The performance of this online method relative to the standardized off-line thermo-optical OC–EC method and respective instruments was evaluated during a winter field campaign at an urban background location in Ljubljana, Slovenia. The organic-matter-to-organic-carbon ratio obtained from the comparison with an aerosol chemical speciation monitor (ACSM) was OM/OC=1.8, in the expected range.

Carbonaceous aerosols (CA), composed of black carbon (BC) and organic matter (OM), significantly impact the climate. Light absorption properties of CA, particularly of BC and brown carbon (BrC), are crucial due to their contribution to global and regional warming. We present the absorption properties of BC (b Abs,BC ) and BrC (b Abs,BrC ) inferred using Aethalometer data from 44 European sites covering different environments (traffic (TR), urban (UB), suburban (SUB), regional background (RB) and mountain (M)). Absorption coefficients showed a clear relationship with station setting decreasing as follows: TR > UB > SUB > RB > M, with exceptions. The contribution of b Abs,BrC to total absorption (b Abs ), i.e. %Abs BrC , was lower at traffic sites (11-20 %), exceeding 30 % at some SUB and RB sites. Low AAE values were observed at TR sites, due to the dominance of internal combustion emissions, and at some remote RB/M sites, likely due to the lack of proximity to BrC sources, insufficient secondary processes generating BrC or the effect of photobleaching during transport. Higher b Abs and AAE were observed in Central/Eastern Europe compared to Western/Northern Europe, due to higher coal and biomass burning emissions in the east. Seasonal analysis showed increased b Abs , b Abs,BC , b Abs,BrC in winter, with stronger %Abs BrC , leading to higher AAE. Diel cycles of b Abs,BC peaked during morning and evening rush hours, whereas b Abs,BrC , %Abs BrC , AAE, and AAE BrC peaked at night when emissions from household activities accumulated. Decade-long trends analyses demonstrated a decrease in b Abs , due to reduction of BC emissions, while b Abs,BrC and AAE increased, suggesting a shift in CA composition, with a relative increase in BrC over BC. This study provides a unique dataset to assess the BrC effects on climate and confirms that BrC can contribute significantly to UV-VIS radiation presenting highly variable absorption properties in Europe., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Griša Močnik, Asta Gregorič, Matic Ivančič and Martin Rigler were or are employed by the manufacturer of the instruments used in this study., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Greater Cairo, the largest megacity of the Middle East North Africa (MENA) region, is currently suffering from major aerosol pollution, posing a significant threat to public health. However, the main sources of pollution remain insufficiently characterized due to limited atmospheric observations. To bridge this knowledge gap, we conducted a continuous 2-month field study during the winter of 2019-2020 at an urban background site, documenting for the first time the chemical and physical properties of submicron (PM 1 ) aerosols. Crustal material from both desert dust and road traffic dust resuspension contributed as much as 24 % of the total PM 1 mass (rising to 66 % during desert dust events), a figure not commonly observed in urban environments. Our observations showed significant decreases in black carbon concentrations and ammonium sulfate compared to data from 15 years ago, indicating an important reduction in both local and regional emissions as a result of effective mitigation measures. The diurnal variability of carbonaceous aerosols was attributed to emissions emanating from local traffic at rush hours and nighttime open biomass burning. Surprisingly, semi-volatile ammonium chloride (NH 4 Cl) originating from local open biomass and waste burning was found to be the main chemical species in PM 1 over Cairo. Its nighttime formation contributed to aerosol water uptake during morning hours, thereby playing a major role in the build-up of urban haze. While our results confirm the persistence of a significant dust reservoir over Cairo, they also unveil an additional source of highly hygroscopic (semi-volatile) inorganic salts, leading to a unique type of urban haze. This haze, with dominant contributors present in both submicron (primarily as NH 4 Cl) and supermicron (largely as dust) modes, underscores the potential implications of heterogeneous chemical transformation of air pollutants in urban environments., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Light-absorbing aerosols heat the atmosphere; an accurate quantification of their absorption coefficient is mandatory. However, standard reference instruments (CAPS, MAAP, PAX, PTAAM) are not always available at each measuring site around the world. By integrating all previous published studies concerning the Aethalometers, the AE33 filter loading parameter, provided by the dual-spot algorithm, were used to determine the multiple scattering enhancement factor from the Aethalometer itself (hereinafter C AE ) on an yearly and a monthly basis. The method was developed in Milan, where Aethalometer measurements were compared with MAAP data; the comparison showed a good agreement in terms of equivalent black carbon (R 2  = 0.93; slope = 1.02 and a negligible intercept = 0.12 μg m -3 ) leading to a yearly experimental multiple scattering enhancement factor of 2.51 ± 0.04 (hereinafter C MAAP ). On a yearly time base the C AE values obtained using the new approach was 2.52 ± 0.01, corresponding to the experimental one (C MAAP ). Considering the seasonal behavior, higher experimental C MAAP and computed C AE values were found in summer (2.83 ± 0.12) whereas, the lower ones in winter/early-spring (2.37 ± 0.03), in agreement with the single scattering albedo behavior in the Po Valley. Overall, the agreement between the experimental C MAAP and C AE showed a root mean squared error (RMSE) of just 0.038 on the C MAAP prediction, characterized by a slope close to 1 (1.001 ± 0.178), a negligible intercept (-0.002 ± 0.455) and a high degree of correlation (R 2  = 0.955). From an environmental point of view, the application of a dynamic (space/time) determination of C AE increases the accuracy of the aerosol heating rate (compared to applying a fixed C value) up to 16 % solely in Milan, and to 114 % when applied in the Arctic at 80°N., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Luca Ferrero reports financial support was provided by University of Milan-Bicocca., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Source apportionment (SA) techniques allocate the measured ambient pollutants with their potential source origin; thus, they are a powerful tool for designing air pollution mitigation strategies. Positive Matrix Factorization (PMF) is one of the most widely used SA approaches, and its multi-time resolution (MTR) methodology, which enables mixing different instrument data in their original time resolution, was the focus of this study. One year of co-located measurements in Barcelona, Spain, of non-refractory submicronic particulate matter (NR-PM 1 ), black carbon (BC) and metals were obtained by a Q-ACSM (Aerodyne Research Inc.), an aethalometer (Aerosol d.o.o.) and fine offline quartz-fibre filters, respectively. These data were combined in a MTR PMF analysis preserving the high time resolution (30 min for the NR-PM 1 and BC, and 24 h every 4th day for the offline samples). The MTR-PMF outcomes were assessed varying the time resolution of the high-resolution data subset and exploring the error weightings of both subsets. The time resolution assessment revealed that averaging the high-resolution data was disadvantageous in terms of model residuals and environmental interpretability. The MTR-PMF resolved eight PM 1 sources: ammonium sulphate + heavy oil combustion (25%), ammonium nitrate + ammonium chloride (17%), aged secondary organic aerosol (SOA) (16%), traffic (14%), biomass burning (9%), fresh SOA (8%), cooking-like organic aerosol (5%), and industry (4%). The MTR-PMF technique identified two more sources relative to the 24 h base case data subset using the same species and four more with respect to the pseudo-conventional approach mimicking offline PMF, indicating that the combination of both high and low TR data is significantly beneficial for SA. Besides the higher number of sources, the MTR-PMF technique has enabled some sources disentanglement compared to the pseudo-conventional and base case PMF as well as the characterisation of their intra-day patterns., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

The Camp Fire was one of California's deadliest and most destructive wildfires, and its widespread smoke threatened human health over a large area in Northern California in November 2018. To analyze the Camp Fire influence on air quality on a 200 km distant site in Berkeley, highly time-resolved total carbon (TC), black carbon (BC), and organic carbon (OC) were measured using the Carbonaceous Aerosol Speciation System (CASS, Aerosol Magee Scientific), comprising two instruments, a Total Carbon Analyzer TCA08 in tandem with an Aethalometer AE33. During the period when the air quality was affected by wildfire smoke, the BC concentrations increased four times above the typical air pollution level presented in Berkeley before and after the event, and the OC increased approximately ten times. High-time-resolution measurements allow us to study the aging of OC and investigate how the characteristics of carbonaceous aerosols evolve over the course of the fire event. A higher fraction of secondary carbonaceous aerosols was observed in the later phase of the fire. At the same time, the amount of light-absorbing organic aerosol (brown carbon) declined with time.

Particulate matter (PM) pollution is one of the major threats to cultural heritage outdoors. It has been recently implied that organic aerosols will prevail over inorganic carbon particulates in the future, changing the main mechanisms of damage caused by poor air quality to calcareous heritage in particular. We studied fresh particulate deposits on marble and limestone surfaces exposed to urban air in sheltered and unsheltered configurations. Due to different air pollution sources in different seasons, the amount and composition of surface deposits varied throughout the year. The main and most constant contributor to PM 2.5 (particles smaller than 2.5 μm) were primary traffic emissions (30 %), followed by secondary formation of acidic inorganic aerosols, such as sulphate in summer and nitrate in winter (33 % altogether), and seasonal biomass-burning emissions (14 %). Although biomass burning is the major source of primary organic aerosols including the light-absorbing fraction that prevailed over black carbon (BC) in colder months (up to 60 % carbonaceous aerosol mass), we show that surface darkening causing the soiling effect is still governed by the minor BC fraction of atmospheric aerosols, which remained below 20 % of the carbonaceous aerosol mass throughout the year. This, however, can change in remote environments affected by biomass-burning emissions, such as winter resorts, or by rigorous BC mitigation measures in the future. In the short run, sheltered positions were less affected by different removal processes, but we show that surface deposits are not simply additive when considering longer periods of time. This must be taken into account when extrapolating surface accumulation to longer time scales., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Asta Gregorič, Matic Ivančič and Martin Rigler are employed by the company Aerosol d.o.o., which develops and manufactures aerosol instrumentation, including the CASS instrument used in the campaigns., (Copyright © 2022 Elsevier B.V. All rights reserved.)

The comprehensive chemical description of air pollution is a prerequisite for understanding atmospheric transformation processes and effects on climate and environmental health. In this study, a prototype vacuum photoionization Orbitrap mass spectrometer was evaluated for field-suitability by an online on-site investigation of emissions from a ship diesel engine. Despite remote measurements in a challenging environment, the mass spectrometric performance could fully be exploited. Due to the high resolution and mass accuracy in combination with resonance-enhanced multiphoton ionization, the aromatic hydrocarbon profile could selectively and sensitively be analyzed. Limitations from commonly deployed time-of-flight platforms could be overcome, allowing to unraveling the oxygen- and sulfur-containing compounds. Scan-by-scan evaluation of the online data revealed no shift in exact m / z , assignment statistics with root mean square error (RMSE) below 0.2 ppm, continuous high-resolution capabilities, and good isotopic profile matches. Emissions from three different feed fuels were investigated, namely, diesel, heavy fuel oil (HFO), and very low sulfur fuel oil (VLSFO). Regulations mainly concern the fuel sulfur content, and thus, exhaust gas treatment or new emerging fuels, such as the cycle-oil-based VLSFO, can legally be applied. Unfortunately, despite lower CHS-class emissions, a substantial amount of PAHs is emitted by the VLSFO with higher aromaticity compared to the HFO. Hence, legislative measures might need to take further chemical criteria into account.

In recent years, carbonaceous aerosols (CA) have been recognized as a significant contributor to the concentration of particles smaller than 2.5 μm (i.e., PM 2.5 ), with a negative impact on public health and Earth's radiative balance. In this study, we present a method for CA apportionment based on high-time-resolution measurements of total carbon (TC), black carbon (BC), and spectral dependence of absorption coefficient using a recently developed Carbonaceous Aerosol Speciation System (CASS). Two-year-long CA measurements at two different locations within California's Los Angeles Basin are presented. CA was apportioned based on its optical absorption properties, organic or elemental carbon composition, and primary or secondary origin. We found that the secondary organic aerosols (SOA), on average, represent >50 % of CA in the study area, presumably resulting from the oxidation of anthropogenic and biogenic volatile organic components. Remarkable peaks of SOA in summer afternoons were observed, with a fractional contribution of up to 90 %. On the other hand, the peak of primary emitted CA, consisting of BC and primary organic aerosol (POA), contributed >80 % to the CA during morning rush hours on winter working days. The light absorption of BC dominated over the brown carbon (BrC), which contributed to 20 % and 10 % of optical absorption at the lower wavelength of 370 nm during winter nights and summer afternoons, respectively. The highest contribution of BrC, up to 50 %, was observed during the wildfire periods. Although the uncertainty levels can be high for some CA components (such as split between primary emitted and secondary formed BrC during winter nights), further research focused on the optical properties of CA at different locations may help to better constrain the parameters used in CA apportionment studies. We believe that the CASS system combined with the apportionment method presented in this study can offer simplified and cost-effective insights into the composition of carbonaceous aerosols., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: At the time of the research, Matic Ivančič, Asta Gregorič, Gašper Lavrič, Bálint Alföldy, Irena Ježek, and Martin Rigler were also employed by the manufacturer of the Aethalometer and Total carbon analyzer instruments. Other authors declare no conflict of interest. The views expressed in this document are solely those of the authors and do not necessarily reflect those of the South Coast AQMD., (Copyright © 2022 The Authors. Published by Elsevier B.V. All rights reserved.)

Accurate and temporally consistent measurements of light absorbing aerosol (LAA) heating rate (HR) and of its source apportionment (fossil-fuel, FF; biomass-burning, BB) and speciation (black and brown Carbon; BC, BrC) are needed to evaluate LAA short-term climate forcing. For this purpose, wavelength- and time-dependent accurate LAA absorption coefficients are required. HR was experimentally determined and apportioned (sources/species) in the EMEP/ACTRIS/COLOSSAL-2018 winter campaign in Milan (urban-background site). Two Aethalometers (AE31/AE33) were installed together with a MAAP, CPC, OPC, a low volume sampler (PM 2.5 ) and radiation instruments. AE31/AE33 multiple-scattering correction factors (C) were determined using two reference systems for the absorption coefficient: 1) 5-wavelength PP_UniMI with low time resolution (12 h, applied to PM 2.5 samples); 2) timely-resolved MAAP data at a single wavelength. Using wavelength- and time-independent C values for the AE31 and AE33 obtained with the same reference device, the total HR showed a consistency (i.e. reproducibility) with average values comparable at 95% probability. However, if different reference devices/approaches are used, i.e. MAAP is chosen as reference instead of a PP_UniMI, the HR can be overestimated by 23-30% factor (by both AE31/AE33). This became more evident focusing on HR apportionment: AE33 data (corrected by a wavelength- and time-independent C) showed higher HR FF (+24 ± 1%) and higher HR BC (+10 ± 1%) than that of AE31. Conversely, HR BB and HR BrC were -28 ± 1% and -29 ± 1% lower for AE33 compared to AE31. These inconsistencies were overcome by introducing a wavelength-dependent C λ for both AE31 and AE33, or using multi-wavelength apportionment methods, highlighting the need for further studies on the influence of wavelength corrections for HR determination. Finally, the temporally-resolved determination of C resulted in a diurnal cycle of the HR not statistically different whatever the source- speciation- apportionment used., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Asbestos is a known human carcinogen and the chief known cause of mesothelioma. In 1997, a group of experts developed the Helsinki Criteria, which established criteria for attribution of mesothelioma to asbestos. The criteria include two methods for causation attribution: 1) a history of significant occupational, domestic, or environmental exposure and/or 2) pathologic evidence of exposure to asbestos. In 2014, the Helsinki Criteria were updated, and these attribution criteria were not changed. However, since the Helsinki Criteria were first released in 1997, some pathologists, cell biologists, and others have claimed that a history of exposure cannot establish causation unless the lung asbestos fiber burden exceeds "the background range for the laboratory in question to attribute mesothelioma cases to exposure to asbestos." This practice ignores the impact on fiber burden of clearance/translocation over time, which in part is why the Helsinki Criteria concluded that a history of exposure to asbestos was independently sufficient to attribute causation to asbestos. After reviewing the Helsinki Criteria, we conclude that their methodology is fatally flawed because a quantitative assessment of a background lung tissue fiber level cannot be established. The flaws of the Helsinki Criteria are both technical and substantive. The 1995 paper that served as the scientific basis for establishing background levels used inconsistent methods to determine exposures in controls and cases. In addition, historic controls cannot be used to establish background fiber levels for current cases because ambient exposures to asbestos have decreased over time and control cases pre-date current cases by decades. The use of scanning electron microscope (SEM) compounded the non-compatibility problem; the applied SEM cannot distinguish talc from anthophyllite because it cannot perform selected area electron diffraction, which is a crucial identifier in ATEM for distinguishing the difference between serpentine asbestos, amphibole asbestos, and talc., Competing Interests: Dr. David Egilman serves as an expert witness in litigation at the request of people who claim injuries resulting from the use of talcum powders. He has also served as an expert witness at the request of companies who have been sued for exposure to asbestos from their mines or products. He was not compensated for work on this commentary. No party to these litigations reviewed this commentary or had input into its content. Dr. Mark Rigler serves as an expert witness in litigation at the request of people who claim injuries resulting from the use of talcum powders. He was not compensated for work on this commentary. Dr. Theresa Emory has testified in asbestos litigation, primarily for plaintiffs. Triet Tran works for Dr. Egilman., (Copyright: © 2021 The Author(s).)

State-of-the-art mass spectrometry with ultraviolet (UV) photoionization is mostly limited to time-of-flight (ToF) mass spectrometers with 1000-10 000 m /Δ m mass resolution. However, higher resolution and higher spectral dynamic range mass spectrometry may be indispensable in complex mixture characterization. Here, we present the concept, implementation, and initial evaluation of a compact ultrahigh-resolution mass spectrometer with gas-phase laser ionization. The concept is based on direct laser photoionization in the ion accumulation and ejection trap (C-trap) of an Orbitrap mass spectrometer. Resonance-enhanced multiphoton ionization (REMPI) using 266 nm UV pulses from a frequency-quadrupled Nd:YAG laser was applied for selective and efficient ionization of monocyclic and polycyclic aromatic hydrocarbons. The system is equipped with a gas inlet for volatile compounds and a heated gas chromatography coupling. The former can be employed for rapid system m / z -calibration and performance evaluation, whereas the latter enables analysis of semivolatile and higher-molecular-weight compounds. The capability to evaluate complex mixtures is demonstrated for selected petrochemical materials. In these experiments, several hundred to over a thousand compounds could be attributed with a root-mean-square mass error generally below 1 ppm and a mass resolution of over 140 000 at 200 m / z . Isobaric interferences could be resolved, and narrow mass splits, such as 3.4 mDa (SH 4 /C 3 ), are determined. Single laser shots provided limits of detection in the 20-ppb range for p-xylene and 1,2,4-trimethylbenzene, similar to compact vacuum REMPI-ToF systems.

Background & Aims: Patients in the Intensive Care Unit (ICU) are at high risk of malnutrition. The only validated malnutrition assessment tool is the Subjective Global Assessment (SGA). The Global Leadership Initiative on Malnutrition (GLIM) is a new malnutrition assessment tool. The present study compares the nutrition-related parameters of the following tools: GLIM tool, SGA, Phase Angle (PA), Low Fat-Free Mass Index (FFMI), and Patient- and Nutrition-Derived Outcome Risk Assessment score (PANDORA), in an attempt to validate an objective tool., Methods: Eighty-four ICU patients were included. The tools mentioned above were assessed for their validity in diagnosing malnutrition. All patients were defined as suffering from acute disease and received medical nutrition therapy. To evaluate whether there is a correlation between the GLIM criteria, SGA, PA, and low FFMI, we compared the SGA, PA, and low FFMI to the GLIM criteria using Spearman correlation coefficients and a Chi-square test. Also, a Mann-Whitney U test was used to test the mean differences between the GLIM criteria and the PANDORA. The area under the curve (AUC) of the proposed parameters was evaluated for diagnosis of malnutrition to seek cutoff points that yield good sensitivity and specificity., Results: Mean age was 50 ± 20 years, BMI 25.3 ± 5.1 kg/m 2 , APACHE II 20.5 ± 7.7, PANDORA score 32 ± 8.5. GLIM malnutrition criteria were significantly correlated with the gold standard SGA assessment and with low FFMI, with PA (Phase Angle), and with the PANDORA score. The area under the curve, by using the ROC curve analysis for GLIM criteria stratified by the SGA results, was 0.85 (P < 0.001). Sensitivity was 85%, and specificity 79%. However, when comparing the low FFMI, PA, and PANDORA to the GLIM criteria, the ROC curve analysis results were considered poor rank., Conclusions: The SGA malnutrition assessment highly validated the GLIM criteria framework combined with the two-criteria diagnosis of malnutrition with a high level of precision. The GLIM malnutrition assessment seems to be acceptable in the ICU setting., Competing Interests: Conflict of interest The authors have no conflicts of interest to declare., (Copyright © 2020 Elsevier Ltd and European Society for Clinical Nutrition and Metabolism. All rights reserved.)

Background & Aims: Enteral nutrition (EN) and parenteral nutrition (PN) enriched with omega-3 polyunsaturated fatty acids (PUFA) have beneficial effects in critical illness. This study aimed to assess the combined effect of EN and supplemental PN enriched with omega-3 PUFA on blood oxygenation in intensive care unit (ICU) patients., Methods: Single-center, prospective, randomized, controlled, double-blind, phase III trial conducted from 10/2013 to 11/2017. A total of 100 ICU patients (18-85 years, APACHE II score > 15) requiring mechanical ventilation were randomly assigned to received combined EN and PN either with omega-3 PUFA (omega-3 group) or without (control group) for up to 28 days. Primary endpoint: 'change of PaO 2 /FiO 2 from day (D) 1 to D4'. Secondary endpoints: lung function parameters, ICU complications, length of hospital stay, days free of ICU care/ventilation/sedation/catecholamine treatment, mortality, erythrocyte fatty acid composition, inflammatory parameters. Safety parameters: standard laboratory assessment, vital signs, physical examination, SOFA score, adverse events., Results: Combined EN and PN covered energy requirements to more than 80%. Blood oxygenation (ΔPaO 2 /FiO 2 from D1 to D4: -1.3 ± 83.7, n = 42, and 13.3 ± 86.1, n = 39, in omega-3 and control group, respectively, p = 0.7795) and other lung function parameters did not differ between groups but days free of catecholamine treatment were significantly higher in the omega-3 group (~4 days, p = 0.0481). On D6, significantly more patients in the omega-3 group tolerated EN alone (51.0% vs. 29.8%, p = 0.0342). Eicosapentaenoic acid (EPA) content in erythrocytes was significantly increased in the omega-3 group at last observation compared with the control group (ΔEPA: 0.928 ± 0.808% vs. -0.024 ± 0.190%, p < 0.0001). No further significant group differences were detected., Conclusions: Enteral and supplemental PN both enriched with omega-3 PUFA did not improve lung function but allowed earlier weaning from catecholamine treatment and PN. Supplemental PN succeeded to adequately cover energy requirements in critically ill patients., Trial Registration: www.clinicaltrials.gov, registration number: NCT01162928., Competing Interests: Conflict of interest PS received speaker fees. All the other authors do not declare any conflict of interest., (Copyright © 2021 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Objective: Asbestos is a known cause of ovarian cancer. We report 10 cases of serous ovarian cancer among users of Johnson & Johnson (J&J) asbestos-containing "cosmetic" talc products., Methods: We conducted an asbestos exposure assessment during talc application and analyzed surgical tissues and talc containers for asbestos and talc., Results: Talc was found in all cases and tremolite and/or anthophyllite asbestos was found in 8/10 cases. The asbestos fibers found in the "cosmetic" talc containers matched those found in tissues. We estimated inhaled asbestos dose ranged from 0.38 to 5.18 fiber years., Conclusion: We provide evidence that the inhaled dose of asbestos/fibrous talc from "cosmetic" talc use causes ovarian cancer. The unique combination of the types of asbestiform minerals detected in cancerous tissue and "cosmetic" talc is a fingerprint for exposure to asbestos-containing talc.

Aims: Endothelial progenitor cells (EPCs) have an important role in repair following vascular injury. However, in patients with diabetes, EPC number and function are markedly reduced. It is unclear whether intensive glycaemic control can modify EPC properties in diabetic patients. We aimed to examine whether glycaemic control can improve EPC number and function in patients with long-standing uncontrolled type 2 diabetes., Methods and Results: Thirty-five patients with treated type 2 diabetes and HgA1c ≥ 8.5% were included. Patients were tested at baseline and after 3-4 months of an intensive glycaemic control programme, with the aim of achieving HgA1c of 7%. The diabetes group was compared to 20 patients without diabetes (control). Circulating EPC levels were assessed by flow cytometry for expression of VEGFR2, CD133, and CD34. The capacity of the cells to form colony-forming units (CFUs), and their migration and viability were quantified after 1 week of culture. Patients with diabetes (mean age 61.1 ± 7 years, 28.6% women, disease duration of 19.2 ± 8 years) had a baseline HgA1c of 9.4 ± 0.8%. After the glycaemic control period, HgA1c decreased to 8 ± 0.8%. Circulating EPC levels increased significantly after the intensive control period and reached a level similar to the control group. The number of EPC CFUs also increased significantly after glycaemic control but remained lower than the control group. All EPC functional assays improved following the glycaemic control., Conclusions: In patients with uncontrolled long-standing type 2 diabetes, intensive glycaemic control was associated with an increase in the levels of circulating EPCs, and improvement in their functional properties., (© The European Society of Cardiology 2013 Reprints and permissions:sagepub.co.uk/journalsPermissions.nav.)

Background: It has been previously shown that platelets of patients with diabetes are more reactive and less responsive to anti-platelet drugs compared with platelets from subjects without diabetes. Studies examining the effect of glycemic control on platelet reactivity have yielded conflicting data. Thus, in this study, we sought to explore the effect of tight glycemic control on platelet reactivity in patients with long standing uncontrolled diabetes., Methods: The study included 30 patients with long-standing treated diabetes and a baseline HbA1c level of ≥ 8.5%. All patients were treated with aspirin and statins. Patients were tested at baseline and after 3 months of intensive glycemic and metabolic control. The treatment goal was to achieve a HbA1c level of ≤ 7%. Platelet reactivity was assessed by light transmission aggregation in response to 5 and 10 μM ADP and to 0.5mg/ml arachidonic acid (AA). Additonally, platelet activation was assessed by plasma levels of soluble P-selectin using an enzyme-linked immunosorbent assay., Results: The mean duration of diabetes from the time of diagnosis was 20.46 ± 9.31 years. Baseline HbA1c was 9.4 ± 0.8%. Following the intensive glycemic control period, the HbA1C level decreased to 8.1 ± 0.8% (P < 0.0001). Other laboratory parameters did not change significantly except for triglyceride levels, which decreased. None of the platelet aggregation studies nor P-selectin levels differed between baseline and after 3 months of intensive glycemic control., Conclusions: Intensive glycemic control in patients with longstanding uncontrolled diabetes does not seem to result in a reduction in platelet reactivity., (Copyright © 2014. Published by Elsevier Ltd.)

The formation and dimensions of G-wires by different short G-rich DNA sequences in solution were investigated by dynamic light scattering (DLS) and polyacrilamide gel electrophoresis (PAGE). To explore the basic principles of wire formation, we studied the effects of base sequence, method of preparation, temperature, and oligonucleotide concentration. Both DLS and PAGE show that thermal annealing induces much less macromolecular self-assembly than dialysis. The degree of assembly and consequently length of G-wires (5-6 nm) are well resolved by both methods for DNA sequences with intermediate length, while some discrepancies appear for the shortest and longest sequences. As expected, the longest DNA sequence gives the longest macromolecular aggregates with a length of about 11 nm as estimated by DLS. The quadruplex topologies show no concentration dependence in the investigated DNA concentration range (0.1 mM-0.4 mM) and no structural change upon heating.

Ultrastructural studies of leaves of seven Panicum species in or closely related to the Laxa group and classified as C(3), C(4) or C(3)-C(4) intermediate were undertaken to examine features associated with C(3) and C(4) photosynthesis. The C(3) species Panicum rivulare Trin. had few organelles in bundle sheath cell profiles (2 chloroplasts, 1.1 mitochondria, and 0.3 peroxisomes per cell section) compared to an average of 10.6 chloroplasts, 17.7 mitochondria, and 3.2 peroxisomes per bundle sheath cell profile for three C(3)-C(4) species, Panicum milioides Nees ex Trin., Panicum decipiens Nees ex Trin. and Panicum schenckii Hack. However, two other C(3) species, Panicum laxum Sw. and Panicum hylaeicum Mez, contained about 0.7, 0.5, and 0.3 as many chloroplasts, mitochondria, and peroxisomes, respectively, as in bundle sheath cell profiles of the C(3)-C(4) species. Chloroplasts and mitochondria in bundle sheath cells were larger than those in mesophyll cells for the C(4) species Panicum prionitis Griseb. and the C(3)-C(4) species, but in C(3) species the organelles were similar in size or were smaller in the bundle sheath cells. The C(3)-C(4) species and P. laxum and P. hylaeicum exhibited an unusually close association of organelles in bundle sheath cells with mitochondria frequently surrounded in profile by chloroplasts. The high concentrations in bundle sheath cells of somewhat larger organelles than in mesophyll cells correlates with the reduced photorespiration of the C(3)-C(4) species.