Jolly Aero (Slovenia)

<strong class="journal-contentHeaderColor">Abstract.</strong> Brown carbon (BrC) is a fraction of Organic Aerosols (OA) that absorbs radiation in the ultraviolet and short visible wavelengths. Its contribution to radiative forcing is uncertain due to limited knowledge of its imaginary refractive index (<em>k </em>). This study investigates the variability of <em>k</em> for OA from wildfires, residential, shipping, and traffic emission sources over Europe. The MONARCH atmospheric chemistry model simulated OA concentrations and source contributions, feeding an offline optical tool to constrain <em>k</em> values at 370 nm. The model was evaluated against OA mass concentrations from Aerosol Chemical Speciation Monitors (ACSM) and filter sample measurements, and aerosol light absorption measurements at 370 nm derived from Aethalometer^TM from 12 sites across Europe. Results show that MONARCH captures the OA temporal variability across environments (regional, suburban and urban background). Residential emissions are a major OA source in colder months, while secondary organic aerosols (SOA) dominate in warmer periods. Traffic is a minor primary OA contributor. Biomass and coal combustion significantly influence OA absorption, with shipping emissions also notable near harbors. Optimizing <em>k</em> values at 370 nm revealed significant variability in OA light absorption, influenced by emission sources and environmental conditions. Derived <em>k</em> values for biomass burning (0.03 to 0.13), residential (0.008 to 0.13), shipping (0.005 to 0.08), and traffic (0.005 to 0.07) sources improved model representation of OA absorption compared to a constant <em>k</em>. Introducing such emission source-specific constraints is an innovative approach to enhance OA absorption in atmospheric models.

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 (OA) and black carbon (BC). While BC is recognized for its large light absorption cross-section, the role of OA in light absorption is still under evaluation due to their heterogeneous composition and source-dependent optical properties. Studies that characterize wood-burning aerosol emissions in Europe typically focus on urban and background sites and only cover BC properties. However, RWB is more prevalent in rural areas, and the present scenario indicates that an improved understanding of the RWB aerosol optical properties and their subsequent connection to climate impacts is necessary for 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 01.12.2017 to 07.03.2018. 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 34.8 µg m -3 (max = 271.8 µg m -3 ) and 3.1 µg m -3 (max = 24.3 µg m -3 ), respectively. The mean total particle number concentration (10-600 nm) was 9.9 x 10 3 particles cm -3 (max = 53.5 x 10 3 particles cm -3 ). The mean total light absorption coefficient at 370 nm and 880 nm measured by an Aethalometer AE33 were 122.8 Mm -1 and 15.3 Mm -1 and had maximum values of 1103.9 Mm -1 and 179.1 Mm -1 , respectively. The aerosol concentrations and absorption coefficients measured during the campaign in Loški Potok were significantly larger than those reported values for several urban areas in the region with larger populations and extent of aerosol sources.

&amp;lt;p&amp;gt;The impact of cloud fraction and cloud type on the heating rate (HR) of black and brown carbon (HR&amp;lt;sub&amp;gt;BC&amp;lt;/sub&amp;gt; and HR&amp;lt;sub&amp;gt;BrC&amp;lt;/sub&amp;gt;) was experimentally determined using a methodology developed in a previous study (Ferrero et al., 2018). High time-resolution measurements of the aerosol absorption coefficient at multiple-wavelengths (Aethalometer AE33 calibrated in COLOSSAL Campaign, Ferrero et al., 2021a) were coupled with spectral measurements of the direct, diffuse and surface reflected irradiance (Multiplexer-Radiometer-Irradiometer coupled with LSI-Lastem DPA154 and C201R, class 1 radiometers), and with lidar-ceilometer (Jenoptik Nimbus 15k biaxial lidar-ceilometer) during a one year field campaign in Milan, Po Valley (Italy).&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;The set-up allowed the experimental determination of the total HR (and its speciation: HR&amp;lt;sub&amp;gt;BC&amp;lt;/sub&amp;gt; and HR&amp;lt;sub&amp;gt;BrC&amp;lt;/sub&amp;gt;) in all sky conditions (from clear-sky to cloudy) with the highest total HR values found in the middle of winter (1.43&amp;amp;#177;0.05 K day&amp;lt;sup&amp;gt;-1&amp;lt;/sup&amp;gt;). The HR&amp;lt;sub&amp;gt;BrC&amp;lt;/sub&amp;gt; accounted for 13.7&amp;amp;#177;0.2% of the total HR (BrC absorption Angstrom exponent: 3.49&amp;amp;#177;0.01).&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Sky conditions were classified in terms of cloudiness (fraction of sky covered by clouds: oktas) and cloud types: 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, the remaining time (77%) being characterized by cloudy conditions. The average cloudiness was 3.58&amp;amp;#177;0.04 oktas (highest in February: 4.56&amp;amp;#177;0.07 oktas, lowest in November: 2.91&amp;amp;#177;0.06 oktas). St were mostly responsible of overcast conditions (oktas=7-8, frequency: 87 and 96%).&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;HR measurements showed a constant decrease with increasing cloudiness allowing to quantify the bias (in %) of the aerosol HR introduced by the simplified assumption of clear-sky conditions in radiative transfer model calculations. Results showed that the HR of light absorbing aerosol was ~20-30% lower in low cloudiness (oktas=1-2) up to 80% lower in complete overcast conditions (i.e., oktas=7-8), compared to clear sky ones. The impact of different cloud types on the HR was also investigated. Cirrus were found to have a modest impact, decreasing the HR&amp;lt;sub&amp;gt;BC&amp;lt;/sub&amp;gt; and HR&amp;lt;sub&amp;gt;BrC&amp;lt;/sub&amp;gt; by -5% at most. Cumulus decreased the HR&amp;lt;sub&amp;gt;BC&amp;lt;/sub&amp;gt; and HR&amp;lt;sub&amp;gt;BrC&amp;lt;/sub&amp;gt; by -31&amp;amp;#177;12 and -26&amp;amp;#177;7%, respectively; cirrocumulus-cirrostratus decreased the HR&amp;lt;sub&amp;gt;BC&amp;lt;/sub&amp;gt; and HR&amp;lt;sub&amp;gt;BrC&amp;lt;/sub&amp;gt; by -60&amp;amp;#177;8 and -54&amp;amp;#177;4%, which was comparable to the impact of altocumulus (-60&amp;amp;#177;6 and -46&amp;amp;#177;4%). A higher impact on HR&amp;lt;sub&amp;gt;BC&amp;lt;/sub&amp;gt; and HR&amp;lt;sub&amp;gt;BrC&amp;lt;/sub&amp;gt; suppression was found for stratocumulus (-63&amp;amp;#177;6 and -58&amp;amp;#177;4%, respectively) and altostratus (-78&amp;amp;#177;5 and -73&amp;amp;#177;4%, respectively). The highest impact was associated to stratus, suppressing the HR&amp;lt;sub&amp;gt;BC&amp;lt;/sub&amp;gt; and HR&amp;lt;sub&amp;gt;BrC&amp;lt;/sub&amp;gt; by -85&amp;amp;#177;5 and -83&amp;amp;#177;3%, respectively. The presence of clouds caused a decrease of both HR&amp;lt;sub&amp;gt;BC&amp;lt;/sub&amp;gt; and HR&amp;lt;sub&amp;gt;BrC&amp;lt;/sub&amp;gt; (normalized to the absorption coefficient of the respective species) of -11.8&amp;amp;#177;1.2% and -12.6&amp;amp;#177;1.4% per okta&amp;amp;#160; (Ferrero et al., 2021b) allowing to parametrize the BC and BrC radiative impact in non clear sky conditions around the world.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;

Abstract. 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 %).

Abstract. We experimentally quantified the impact of cloud fraction and cloud type on the heating rates (HRs) of black and brown carbon (HRBC and HRBrC).In particular, in this work, we examine in more detail the average cloud effect (Ferrero et al., 2018) using high time-resolution measurements of aerosol absorption at multiple-wavelengths coupled with spectral measurements of the direct, diffuse and surface reflected radiation and lidar data in the Po Valley. The experimental set-up allowed a direct determination of HRBC and HRBrC in any sky condition. The highest values of total HR were found in the middle of the winter (1.43 ± 0.05 K day−1) while the lowest in spring (0.54 ± 0.02 K day−1) Overall the HRBrC accounted for 13.7 ± 0.2 % of the total HR, the BrC being characterized by an AAE of 3.49 ± 0.01. Simultaneously, sky conditions were classified (from clear-sky to cloudy) in terms of fraction of sky covered by clouds (oktas) and cloud types. Cloud types were grouped as a function of altitude into the following classes: 1) low level ( 7 km) cirrus, cirrocumulus-cirrostratus. Measurements carried out in different sky conditions at high-time resolution showed a constant decrease of HR with increasing cloudiness of the atmosphere enabling us to quantify for the first time the bias (in %) in the aerosol HR introduced by improperly assuming clear-sky conditions in radiative transfer calculations. In fact, during the campaign, clear sky conditions were only present 23 % of the time while the remaining time (77 %) was characterized by cloudy conditions. Our results show that, by incorrectly assuming clear-sky conditions, the HR of light absorbing aerosol can be largely overestimated (by 50 % in low cloudiness, oktas = 1–2), up to over 400 % (in complete overcast conditions, i.e., oktas = 7–8). The impact of different cloud types on the HR compared to a clear sky condition was also investigated. Cirrus were found to have a modest impact, decreasing the HRBC and HRBrC by −1– −5 %. Cumulus decreased the HRBC and HRBrC by −31 ± 12 and −26 ± 7 %, respectively, while cirrocumulus-cirrostratus by −60 ± 8 and −54 ± 4 %, which was comparable to the impact of altocumulus (−60 ± 6 and −46 ± 4 %). A high impact on HRBC and HRBrC was found for stratocumulus (−63 ± 6 and −58 ± 4 %, respectively) and altostratus (−78 ± 5 and −73 ± 4 %, respectively), although the highest impact was found to be associated to stratus that suppressed the HRBC and HRBrC by −85 ± 5 and −83 ± 3 %, respectively. Additionally, the cloud influence on the radiation spectrum that interacts with the absorbing aerosol was investigated. Black and brown carbon (BC and BrC) have different spectral responses (a different absorption Angstrom exponent, AAE) and our results show that the presence of clouds causes a greater decrease for the HRBC with respect to to HRBrC going clear sky to complete overcast conditions; the observed the difference is 12 ± 6 %. This means that, compared to BC, BrC is more efficient in heating the surrounding atmosphere in cloudy conditions than in clear sky. Overall, this study extends the results of a previous work (Ferrero et al., 2018), highlighting the need to take into account both the role of cloudiness and of different cloud types to better estimate the HR associated to both BC and BrC, and in turn decrease the uncertainties associated to the quantification of the impact of these species on radiation and climate.

Abstract. We present the newly developed Total Carbon Analyzer (TCA08), and a new 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 μgC, which corresponds to a concentration of 0.3 μgC/m3 at a sample flow rate of 16.7 LPM and a 1-hour sampling time base. The concentration of particulate 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 TCA08 and Aethalometer (AE33) is an easy-to-deploy and low maintenance continuous measurement technique for the high time resolution determination of organic and elemental carbon (EC) in different particulate matter size fractions, which avoids pyrolytic correction and need for high purity compressed gases. The equivalence of this new online method to the standardized off-line thermo-optical OC-EC methods 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.