Light absorbing aerosols (LAA) absorb sunlight and heat the atmosphere. This work presents a novel methodology to experimentally quantify the heating rate (HR) induced by LAA into an atmospheric ...layer. Multiwavelength aerosol absorption measurements were coupled with spectral measurements of the direct, diffuse and surface reflected radiation to obtain highly time-resolved measurements of HR apportioned in the context of LAA species (black carbon, BC; brown carbon, BrC; dust), sources (fossil fuel, FF; biomass burning, BB), and as a function of cloudiness. One year of continuous and time-resolved measurements (5 min) of HR were performed in the Po Valley. We experimentally determined (1) the seasonal behavior of HR (winter 1.83 ± 0.02 K day–1; summer 1.04 ± 0.01 K day–1); (2) the daily cycle of HR (asymmetric, with higher values in the morning than in the afternoon); (3) the HR in different sky conditions (from 1.75 ± 0.03 K day–1 in clear sky to 0.43 ± 0.01 K day–1 in complete overcast); (4) the apportionment to different sources: HRFF (0.74 ± 0.01 K day–1) and HRBB (0.46 ± 0.01 K day–1); and (4) the HR of BrC (HRBrC: 0.15 ± 0.01 K day–1, 12.5 ± 0.6% of the total) and that of BC (HRBC: 1.05 ± 0.02 K day–1; 87.5 ± 0.6% of the total).
The atmospheric concentration of black carbon (BC) has paramount importance worldwide due to its role in global warming and its adverse effect on human health. Only limited information is available ...about BC concentration and emission factors from the Arabian/Persian Gulf region despite the presence of significant sources including petrochemical industry and maritime shipping. The atmospheric concentrations of BC, nitrogen oxides (NO, NO2), ozone and particulate matter (PM10) were monitored at a suburban location and at a central residential location in Doha, Qatar during fall-spring 2016–2017. Elevated NOX and BC mean concentrations (25.8 ppbv and 5.17 μg/m3 respectively) and maximum values (228 ppbv vs. 27 μg/m3) were measured at both locations. The average ozone mixing ratio was 15.9 ppbv (max. 52.6 ppbv). Typically, the BC concentration was correlated with NOX, which indicates common sources. BC/NOX emission ratios (ER) were calculated to characterise the sources, while the NO/NOX concentration ratio was used as a proxy of pollution age. The calculated BC/NOX emission ratios were found to be high comparing to the EMEP database, with the means of 0.13 μg m−3 ppbv−1 (suburban location) and 0.10 μg m−3 ppbv−1 (residential location). The BC/NOX ER did not show significant daily variation, while the NO/NOX ratio showed typical urban time pattern with high ratio during morning rush hours following by a decreasing trend during afternoon, and minimum values at night-time. The PM10 concentrations were high during the measurement period with a mean of 103 μg m−3, which is typical in the Gulf region. During occasional dust storm events the PM10 hourly average concentration raised peaked at 1054 μg m−3. Significant influence of mineral dust was observed on the BC measurement and the absorption properties, as it was increasing the BC readings and widening the distribution of the absorption Ångström exponent. The mass absorption cross-section of mineral dust was determined during the major dust storm event.
•Black carbon and nitrogen oxides are significant air pollutants in the Gulf region.•Fossil fuel combustion related dominate the black carbon particles.•High BC/NOX emission ratio indicates deficit air combustion like oil or gas flaring.•Mineral dust was detected by the Aethalometer during a major dust storm episode.•High mineral dust interfered the BC measurement and the source apportionment.
A recently-developed radon-based method for combined classification of both diurnal and synoptic timescale changes in the atmospheric mixing state is applied to 1-year of observations in Ljubljana ...(capital of Slovenia). Five diurnal-timescale mixing classes (#1 to #5) were defined for each season along with an additional mixing class (#6) in non-summer months, representative of synoptic-timescale changes of the atmospheric mixing state associated with “persistent temperature inversion” (PTI) events. Seasonal composite radiosonde profiles and mean sea level pressure charts within each mixing class are used to demonstrate the link between prevailing synoptic conditions and the local mixing state, which drives changes in urban air quality. Diurnal cycles of selected pollutants (BC, NO2, CO, PM10, SO2 and O3) exhibited substantial seasonality as a result of changing mixing conditions, source types and strengths. For the more well-mixed conditions (classes #2 to #3), surface wind speeds were 3 times higher than during class #6 (PTI) conditions, resulting in a 3-fold reduction of primary pollutant accumulation. Daily-mean PM10 concentrations only exceeded EU and WHO guideline values in winter and autumn for two of the radon-defined mixing classes: (i) class #5 (strongly stable near-surface conditions associated with passing synoptic anti-cyclone systems), and (ii) class #6 (PTI conditions driven by regional subsidence in the presence of the “Siberian High”). Both mixing states were associated with low mean wind speeds (∼0–0.7 m s−1) and strong thermal stratification, as indicated both by pseudo-vertical temperature gradients (∆T/∆z) and radiosonde profiles. Diurnal ∆T/∆z values indicated limited opportunity for convective mixing of pollutants from the basin atmosphere under these conditions. The demonstrated consistency in atmospheric mixing conditions (vertically and spatially) across the diurnal cycle within each of the defined mixing classes suggests the radon-based classification scheme used in conjunction with 3-D urban sensor networks could be well suited to evaluate mitigation schemes for urban pollution and urban climate.
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•Seasonal application of a radon-based stability classification in an urban basin•Classification method addresses changes on diurnal and synoptic timescales.•Classification scheme applies at large spatial and vertical extents.•New insight gained to controls on urban pollution and times of public exposure.
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., PM2.5), 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.
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•A new method for carbonaceous aerosol apportionment into six components•Focus on the primary or secondary origin and light absorption properties•Long-term (2 years) measurement campaign in two locations in the Los Angeles Basin•High-time-resolution apportionment allows studying diurnal profiles.•Comparable results on both sites with similar seasonal patterns
Aerosol direct radiative forcing is strongly dependent on aerosol distributions and aerosol types. A detailed understanding of such information is still missing at the Alpine region, which currently ...undergoes amplified climate warming. Our goal was to study the vertical variability of aerosol types within and above the Vipava valley (45.87°N, 13.90°E, 125 m a.s.l.) to reveal the vertical impact of each particular aerosol type on this region, a representative complex terrain in the Alpine region which often suffers from air pollution in the wintertime. This investigation was performed using the entire dataset of a dual-wavelength polarization Raman lidar system, which covers 33 nights from September to December 2017. The lidar provides measurements from midnight to early morning (typically from 00:00 to 06:00 CET) to provide aerosol-type dependent properties, which include particle linear depolarization ratio, lidar ratio at 355 nm and the aerosol backscatter Ångström exponent between 355 nm and 1064 nm. These aerosol properties were compared with similar studies, and the aerosol types were identified by the measured aerosol optical properties. Primary anthropogenic aerosols within the valley are mainly emitted from two sources: individual domestic heating systems, which mostly use biomass fuel, and traffic emissions. Natural aerosols, such as mineral dust and sea salt, are mostly transported over large distances. A mixture of two or more aerosol types was generally found. The aerosol characterization and statistical properties of vertical aerosol distributions were performed up to 3 km.
Airborne meteorological and aerosol measurements have been performed in Longyearbyen (Svalbard islands) in the summer of 2018, coupling an instrumental aerosol payload with a meteorological ...radiosonde deployed on a tethered balloon. More than 70 vertical profiles of aerosol and meteorological properties have been recorded up to a maximum altitude of 1.2 km. As a main result, the present work provides a homogeneous gridded dataset of vertical profiles of equivalent black carbon (eBC) and nanoparticles (NP) concentrations and associated meteorological data (temperature, T, relative humidity, RH, pressure, P) to be employed for future modelling studies of Arctic pollution. Mean values (±SD) of eBC and NP below 500 m were 110 ± 10 ng m−3 and 1400 ± 400 particles cm−3, respectively. Mean values above 500 m were 150 ± 30 ng m−3 and 1000 ± 350 particles cm−3, respectively. Group medians of maximum eBC and NP concentrations in vertical profiles with temperature inversions were significantly higher than for those without inversion. The dataset has been complemented by continuous ground measurements of eBC with an average value of 208 ± 130 ng m−3 (median value 110 ± 70 ng m−3) for the entire campaign; the ground-based background (absence of local emission) eBC value was below 100 ng m−3 while maximum values were in the 1000–2000 ng m−3 range. Median eBC concentration measured at ground for 2 h before the tethered balloon launch was higher when temperature inversion was observed. The ground-based measurements, coupled with aerosol optical depth measurements, allowed for a preliminary discussion of two case studies related to high pollutants concentration events.
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 PM2.5 (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.
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•Interaction between heritage materials and airborne particles is poorly understood.•Fresh deposits are characterized to be able to study aging after the deposition.•PM source apportionment is correlated with surface reflectance and chemistry.•Surface deposits resemble main PM sources but do not sum up on long time-scales.•Light absorption by black carbon causing soiling still exceeds that of brown carbon.
Discriminating the absorption coefficients of aerosol mineral dust and black carbon (BC) in different aerosol size fractions is a challenge because of BC's large mass absorption cross-section ...compared to dust. Ambient aerosol wavelength dependent absorption coefficients (babs) in supermicron and submicron size fractions were determined with a high time resolution. The measurements were performed simultaneously using identical systems at an urban and a regional background site in Qatar. At each site, measurements were taken by co-located Aethalometers, one with a virtual impactor (VI) and the other with a PM1 cyclone to respectively collect super-micron-enhanced and submicron fractions. The combined measurement of aerosol absorption and scattering coefficients enabled the particles to be classified based on their optical properties' wavelength dependence. The classification reveals the presence of BC internally/externally mixed with different aerosols. Helium ion microscopy images provided information concerning the extent of mineral dust in the submicron fraction. The determination of absorption coefficients during dust storms and non-dust periods was used to establish the absorption Ångström exponent for dust and BC. Non-parametric wind regression, potential source contribution function and back-trajectory analysis reveal major regional sources of desert dust associated with north-westerly winds and a minor local dust contribution. In contrast, major BC sources found locally were associated with south-westerly winds with a smaller contribution made by offshore emissions transported by north-easterly and easterly winds. The use of a pair of Aethalometers with VI and PM1 inlets separates contributions of BC and dust to the aerosol absorption coefficient.
The text discusses a study focused on discriminating between aerosol mineral dust and BC absorption coefficients in various aerosol size fractions. The key highlights from the text are as follows:•Collocated sites measurements: Measurements were conducted simultaneously at both an urban and a regional background site in Qatar using identical systems. Collocated Aethalometers were used, one with a virtual impactor and the other with a PM1 cyclone, to collect supermicron-enhanced and submicron aerosol fractions, respectively.•Classification based on Optical Properties: The combination of aerosol absorption and scattering coefficient measurements allowed for the classification of particles based on the wavelength dependence of their optical properties, revealing the presence of BC internal/external mixing with various aerosols.•Mineral Dust Contribution: HIM images provided information about the contribution of mineral dust in the submicron aerosol fraction. Absorption coefficients were determined during both dust storms and non-dust periods to calculate AAE for dust and BC.•Source apportionment: Back-trajectories, wind regression, and PSCF were used to identify major regional sources of desert dust associated with northwesterly winds and major local BC sources associated with southerly west winds, with some offshore emissions transported by northeasterly and easterly winds.
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