Effect of Long‐Range Transported Fire Aerosols on Cloud Condensation Nuclei Concentrations and Cloud Properties at High Latitudes

Active vegetation fires in south‐eastern (SE) Europe resulted in a notable increase in the number concentration of aerosols and cloud condensation nuclei (CCN) particles at two high latitude locations—the SMEAR IV station in Kuopio, Finland, and the Zeppelin Observatory in Svalbard, high Arctic. During the fire episode aerosol hygroscopicity κ slightly increased at SMEAR IV and at the Zeppelin Observatory κ decreased. Despite increased κ in high CCN conditions at SMEAR IV, the aerosol activation diameter increased due to the decreased supersaturation with an increase in aerosol loading. In addition, at SMEAR IV during the fire episode, in situ measured cloud droplet number concentration (CDNC) increased by a factor of ∼7 as compared to non‐fire periods which was in good agreement with the satellite observations (MODIS, Terra). Results from this study show the importance of SE European fires for cloud properties and radiative forcing in high latitudes.


Introduction
Wildfire emissions are one of the most prominent sources of atmospheric aerosols and have an important impact on air quality, human health, and climate (Andreae, 2019;Bond et al., 2013).Aerosols from fires affect the climate directly by influencing the radiative forcing through scattering and absorption of solar radiation (Crutzen & Andreae, 1990;Haywood & Boucher, 2000) and indirectly by altering cloud properties (Graaf et al., 2022;Sporre et al., 2014;Spracklen et al., 2011).Fire emissions from biomass burning (BB) produce high concentrations of particulate pollutants, such as black carbon (BC) and brown carbon, that absorb incoming solar radiation (Forrister et al., 2015).Particles emitted from BB are typically larger than 100 nm and easy to act as cloud condensation nuclei (CCN) even at low supersaturations (Reid et al., 2005).Remote sensing and in situ measurements have reported that wildfires lead to increased CCN concentration resulting in more reflective clouds with smaller droplet size (Eagan, 1974;Hegg et al., 2012;Jia et al., 2019;Lathem et al., 2013;H. H. Lee & Wang, 2020;Ross et al., 2003).
Few studies reported enhanced cloud droplet number concentration (CDNC) during forest fires for example, in North America, the Amazon rain forest, Pacific northwest (Conrick et al., 2021;Herbert et al., 2021;Makar et al., 2021;Martins & Silva Dias, 2009), and the western U.S. (Twohy et al., 2021).These modeling/aircraftbased/remote sensing studies have focused on fresh BB smoke, which is chemically very different from aged BB air masses.These observations might not represent the response of cloud microphysical properties to LRT fire airmasses.Several other studies characterized the evolution of LRT smoke plumes but are mainly limited to aerosol physical/optical properties and air quality (Ceamanos et al., 2023;Ditas et al., 2018;Moroni et al., 2017;Pöhlker et al., 2018;Shrestha et al., 2022;Zheng et al., 2020).
In this study, we characterized LRT fire air masses in eastern Finland and a high Arctic location during Autumn 2020.We investigate the changes in aerosol properties in both locations, and the effect of LRT fire aerosols on liquid cloud properties in eastern Finland using in situ observations.Additionally, analysis from satellite observations (MODerate Resolution Imaging Spectroradiometer, MODIS (Terra)) was used to investigate cloud response.This is the first study where a strong cloud response to LRT fire aerosol perturbations in liquid clouds are shown using both in situ and satellite observations.

Experiments and Methods
Measurements in this study were carried out at the SMEAR IV (Station for Measuring Ecosystem-Atmospheric Relations) in Kuopio, eastern Finland from 15.09.2020 to 24.11.2020 and at the Zeppelin Observatory in Ny-Ålesund, Svalbard from 15.09.2020 to 21.10.2020.The SMEAR IV is located on the top of Puijo tower (62.90°N, 27.65°E; 306 m a.s.l and 225 m above lake level), hereafter referred to as "SMEAR-IV" (Leskinen et al., 2009).Additionally, at ground level (200 m below the SMEAR-IV inlets), a "Puijo ground station" was operated to investigate the differences in aerosol properties when the SMEAR-IV was inside and outside a cloud.The Zeppelin Observatory (78.90°N, 11.88°E) is located on the Zeppelin Mountain at 472 m a.s.l. in Svalbard, hereafter referred to as "Zeppelin" An overview of the observational program at the Zeppelin can be found elsewhere (Platt et al., 2022).The locations of the measurement sites are shown in Figure S1 in Supporting Information S1.Both SMEAR-IV and Zeppelin are inside low-level clouds <10% and ∼15% of the time, respectively, due to their topographic prominence.
At SMEAR-IV (on top of the tower), a twin inlet system was used for aerosol sampling (Figure S2a in Supporting Information S1; Portin et al., 2014).The total inlet sampled aerosol particles and cloud droplets with diameters <40 μm.The interstitial inlet has a PM 1 impactor and measured only non-activated aerosol particles (<1 μm).At the Puijo ground station, an inlet with a PM 2.5 impactor was used (Figure S2b in Supporting Information S1).More details about this campaign and stations can be found in Calderón et al. (2022).At Zeppelin, a whole air inlet following the ACTRIS recommendation (Platt et al., 2022) was used to sample the aerosol particles and cloud droplets <40 μm (Figure S2c in Supporting Information S1).
The chemical composition of submicron aerosol particles (NR-PM 1 ; non-refractory particulate matter <1 μm) was measured with a High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS, Aerodyne Research, Inc.) at Puijo ground station and an Aerosol Chemical Speciation Monitor (ACSM, Aerodyne Research, Inc.) at SMEAR-IV and Zeppelin.The aerosol size distribution was measured with Differential Mobility Particle Sizers (DMPS) and equivalent black carbon (eBC) was derived from a Multi-Angle Absorption Photometer (MAAP) at both sites (Texts S1.3-1.4 in Supporting Information S1).Particulate levoglucosan was measured with a Filter Inlet for Gases and AEROsols coupled to a Chemical Ionisation high-resolution time-offlight Mass Spectrometer (FIGAERO-CIMS, Aerodyne Research Inc.) using iodide as a reagent ion at Zeppelin.The aerosol hygroscopicity parameter was derived from the chemical composition data from AMS and ACSM (κ chem ) (See Text S1.7, Table S1 in Supporting Information S1), and the obtained κ chem was used to derive the CCN concentration (N CCN-chem ) from the measured particle size distribution assuming 0.2% supersaturation applying the κ-Köhler theory (Text S1.8, Table S1 in Supporting Information S1; Petters & Kreidenweis, 2007).Additionally, at SMEAR-IV, N CCN was measured directly with a CCN counter, and the cloud droplet number concentration (CDNC) was calculated from the twin inlet DMPS data (Text S1.4 in Supporting Information S1) (Portin et al., 2014).
Back-trajectory analysis was carried out using the Hybrid Single-Particle Lagrangian Integrated Trajectory model (HYSPLITv5.0.0) (Stein et al., 2015).Information about active fires was retrieved from the Fire Information for Resource Management System (FIRMS) by NASA ("MODIS/Aqua Terra Thermal Anomalies/Fire locations 1 km FIRMS V006 NRT (Vector data)," 2015) (Text S1.5 in Supporting Information S1).Additionally, at SMEAR-IV, satellite observations (MODIS, Terra) were carried out and CDNC was calculated with level-2 cloud products from NASA's Earth data portal (Platnick et al., 2003, 2017) (Text S1.4.5 in Supporting Information S1).More details about the instrumentation and data analysis are presented in Text S1 in Supporting Information S1.
During the campaign, a period with a substantial increase in accumulation mode aerosol number concentration, elevated NR-PM 1 and eBC was observed between 23.09.2020 and 10.10.2020 at SMEAR-IV.The mass concentration of NR-PM 1 and eBC during this period increased by a factor of ∼7 when compared to the campaign average (15.09.2020-24.11.2020), reaching a maxima of 25.4 and 1.6 μg m 3 , respectively.Similarly, at Zeppelin, elevated aerosol concentrations were observed between 04.10.2020 and 09.10.2020 with mass concentration of NR-PM 1 and eBC reaching a maximum of 4.5 (5× of campaign average) and 0.41 (∼14× of campaign average) μg m 3 , respectively.
Back-trajectory analysis shows that for these periods of elevated concentrations, more than 60% of the time the air masses came from south-eastern (SE) Europe where active fires from vegetation/grasslands were detected based on FIRMS (Figure S3 in Supporting Information S1).Combining this with the observation of biomass burning tracer compound (discussed in Section 3.1), these episodes are referred to as the "Fire episode" (Text S2.1 in Supporting Information S1).Based on back-trajectory analysis, we associate the detected plumes at both sites with the same fire region (Figures S4a and S4c in Supporting Information S1).The fire emissions were estimated to be ∼1-4 days old when they arrived SMEAR-IV (Figure S5 in Supporting Information S1) and ∼4-8 days at Zeppelin, that is, they were more aged at Zeppelin than at SMEAR-IV.
To quantify the effect of the LRT fire emissions on the aerosol and cloud properties, we defined a reference period for both sites representing unperturbed conditions.For SMEAR-IV, air masses coming from the Atlantic and Arctic (A/A) regions over Scandinavia were relatively clean and considered as typical air masses at this location (Figure S4b in Supporting Information S1).The corresponding periods are classified as non-fire period ("NF period") (Text S2.1 in Supporting Information S1).For Zeppelin, the back-trajectory analysis revealed two other air mass source regions: (a) marine air masses from the North Atlantic (NA, Figure S4d in Supporting Information S1) and (b) air masses coming from the Arctic and Greenland (AG, Figure S4e in Supporting Information S1).The aerosol concentrations were below the ACSM detection limit during NA periods and could not be used.Thus, we used AG periods as the non-fire period (NF).

Effect of Long Range Transported Fire Emission on Aerosol Composition
An overview of the aerosol properties at SMEAR-IV and Zeppelin is shown in Figure 1.At SMEAR-IV, the average mass concentrations of NR-PM 1 and eBC during the campaign were 3.5 ± 4.1 μg m 3 and 0.2 ± 0.3 μg m 3 , respectively.At Zeppelin, the average (±standard deviation) NR-PM 1 and eBC mass concentrations observed for the whole campaign were 0.9 ± 1.1 μg m 3 and 0.03 ± 0.07 μg m 3 , respectively.During the campaign, at SMEAR-IV, the weekly average temperature (±standard deviation) was 11 ± 2°C during the start of the campaign, decreasing gradually to 2 ± 3°C during the final week.At Zeppelin, the ambient temperature was ranging from +7°C to 10°C during the campaign (Text S1.3.3 in Supporting Information S1).
The campaign average NR-PM 1 chemical composition of measured aerosol particles at SMEAR-IV is dominated by organics (67%) followed by sulfate (20%), ammonium (7%), and nitrate (6%).During the NF period, the contribution of inorganics and organics was 21% and 79% (Figure 2a).For the fire episode, the fraction of inorganics increased to 29%, while organics contributed ∼71% of the total NR-PM 1 mass.This increase of the  inorganic fraction could be partly attributed to fire emissions and partly to the influence of anthropogenic emissions.The fire air masses were transported to SMEAR-IV through central and eastern Europe, and heavily affected by industrial, and other terrestrial emissions.Therefore, air masses arriving at SMEAR-IV during the fire episode are affected by both fires from SE Europe and other emissions along the airmass transport route.Interestingly, at Zeppelin, we observed the opposite trend for the inorganic and organic contribution: during the NF period, aerosols had a higher inorganic fraction (44%) than during the fire episode (20%) (Figure 2a).High inorganic mass fractions at Zeppelin during the clean period (NF) are likely due to the influence of marine emissions (Adachi et al., 2022).During the fire episode, the organic mass fraction increased substantially (from 66% to 80%), indicating the impact of the fire emissions and other terrestrial sources.The observed difference in the contribution of organic and inorganic compounds during fire episodes emphasize the importance of background aerosol composition at these locations, as the observed aerosol properties are the result of the superposition of two (background and fire related) aerosol populations.
For the fire episode, an increase in the particle-phase concentration of levoglucosan, a tracer compound for BB, was observed at Zeppelin directly by FIGAERO-CIMS (C 6 H 10 O 5 I ) and at SMEAR-IV as C 2 H 4 O 2 + (m/z 60) with the AMS (Figure S6 in Supporting Information S1).This further confirms the influence of BB emissions during this episode.However, the mass fraction of levoglucosan f 60 (m/z 60/total organic signal) did not increase.This is due to the long aging time of the fire emissions: while the initial levoglucosan is consumed by atmospheric aging (average lifetime 0.7-2.2days, (Li et al., 2021)), new organic material from various sources along the transport route is added to the fire aerosols.Both effects decrease the contribution of the tracer suggesting that the mass ratio of the AMS/ACSM tracer to total organics is not a suitable indicator for aged fire aerosols (Cubison et al., 2011;Hennigan et al., 2010).
For further analysis of composition changes related to the LRT fire aerosols, a positive matrix factorization (PMF) analysis was performed for the high-resolution (HR) organic mass spectra data from AMS at Puijo ground station.
The details of the chosen 5-factor solution are described in Text S2.2 in Supporting Information S1 (Figures S7-S9 in Supporting Information S1).The factors were classified as two local (HOA-hydrocarbon-like Organic Aerosol and LO-OOA-less oxidized-oxygenated OA) and three LRT (MO-OOA-more oxidized-oxygenated OA) factors.The majority of the C 2 H 4 O 2 + ion (m/z 60) signal was attributed to the LRT factors.Additionally, the ratio of m/z 60 to m/z 73 (another BB marker) is ∼1.2 for these factors which is in the range identified for wood burning OA and BBOA (Xu et al., 2020).
The mass contribution of the five PMF-factors for different periods is shown in Figure S9 in Supporting Information S1.During NF periods, the organics are dominated by the local factors with contributions of HOA of 11% and LO-OOA of 42% followed by MO-OOA (LRT factors) (47%).During the fire episode, the contributions from local sources decreased to 6% HOA and 5% LO-OOA while the contribution of MO-OOA increased to 89% indicating the substantial effect of LRT fire emissions in altering the organic composition.OOA are typically more hygroscopic and have higher CCN activity (Duplissy et al., 2011;Rejano et al., 2023) than freshly emitted OA compounds.The effect of increased OOA fraction during the fire episode on aerosol hygroscopicity and CCN properties at SMEAR-IV is discussed in Section 3.3.
Unfortunately, the detailed organic composition at Zeppelin is not yet available for such a comparison.

Aerosol Hygroscopicity and CCN Activity
To understand the effect of LRT fire aerosols on cloud properties, we first studied the average aerosol properties during cloud events for the fire and NF periods.No clouds were detected during the NF period at Zeppelin.Thus, we used the whole NF period average values as a proxy.

Geophysical Research Letters
10.1029/2023GL107134 results in overall higher κ chem values (Table 1), but the difference between the fire and NF period values is similar for both methods.Thus, we used the κ chem calculated with constant κ org in the following section to enable the direct comparison between the two stations.
κ chem at SMEARV-IV was slightly higher during the fire episode when compared to NF period (increased to 0.24 from 0.16) (Figure 2b).This is due to the higher fraction of inorganic compounds (Figure 2a) and MO-OOA (Table 1; Figure S9 in Supporting Information S1), during the fire episode when compared to the NF period.In contrast, at Zeppelin, κ chem decreased to 0.18 during the fire episode from 0.29 in NF period.Aerosols at this location are expected to be mostly marine influenced and unaffected by anthropogenic emissions at this season (Autumn).Thus, the aerosols are rich in inorganics and more hygroscopic, and the addition of any OA could only reduce the hygroscopicity.This observation further highlights the role of the background conditions, that is, whether LRT fire aerosols increase or decrease the aerosol hygroscopicity at a specific location.Note that the reported κ chem values are most likely underestimated for Zeppelin as the ACSM cannot quantify a very hygroscopic compound, sodium chloride (κ = 1.28;Petters & Kreidenweis, 2007) from sea salt, which may be a major constituent in this environment.A mass closure study was performed to obtain a rough estimate of the NaCl concentration (Text S2.2 in Supporting Information S1).κ chem values including NaCl were much higher during the NF period than the Fire episode (Figure S10 and Table S2 in Supporting Information S1), further confirming that the fire air masses reduced the aerosol hygroscopicity at Zeppelin.
The fraction of aerosols that can act as CCN at a given supersaturation depends on the aerosol number size distribution and hygroscopicity.Some studies reported the significance of hygroscopicity (Takeishi et al., 2020;Väisänen et al., 2016) while others found the number/size effect to be dominant (Dusek et al., 2006;Schmale et al., 2018).Jung et al. (2018) reported an increase in N CCN at Zeppelin with an increase in aerosol number concentration (N tot ).During the fire episode the accumulation mode particle concentration increased at both sites.At SMEAR-IV, N tot increased by a factor of ∼1.3 during the fire episode, while at Zeppelin N tot increased by ∼3fold (Table 1).Consequently, the N CCN (0.2% SS) also increased substantially during the fire episode at both sites.But the magnitude of the increase in N CCN at SMEAR-IV is much larger (∼12-fold) than that observed at Zeppelin (∼5.6 -fold) (Figure 2c).This is partly explained by the opposite response in the particle hygroscopicity between fire and NF periods at these locations, indicating the importance of particle hygroscopicity in CCN activation.To quantify the contribution of chemical composition (hygroscopicity) on CCN change, we calculated N CCN using κ chem values from the NF period and the size distributions measured during the fire episode (Text S2.3 in Supporting Information S1).Results show that at SMEAR-IV, the increase in κ chem increased N CCN by 25%, whereas at Zeppelin the reduction in κ chem decreased N CCN by 13% [see Tables S3 and S4 in Supporting Information S1].This shows that the chemical composition change due to LRT fire aerosol has a considerable effect on N CCN at both sites.

Cloud Microphysical Properties
The formation of cloud droplets depends on updraft velocity at a location, temperature, particle size, number concentration, and chemical composition.These parameters influence the smallest diameter of the particles that are activated into cloud droplets, referred to as activation diameter (D act ).At SMEAR-IV, D act can be measured directly with the twin inlet system when the station is in low level clouds (i.e., for a cloud event, Text S1.2 in Supporting Information S1).For a given supersaturation, increasing hygroscopicity lowers the dry particle diameter required for the activation.However, in this study despite higher κ chem values during the fire episode, the average D act (139 ± 21 nm) is higher than that in the NF period (107 ± 30 nm) (Table 1).This is due to the depletion of available water vapor as the higher number of particles in the accumulation mode consumes more of the available water vapor through water uptake during the activation process, lowering the apparent supersaturation.Additionally, comparing NF periods and the fire episode, we observed a ∼7-fold increase of average CDNC (77 ± 24 cm 3 to 521 ± 198 cm 3 ) while N CCN-chem increased by an order of magnitude (∼12×).This discrepancy between the predicted (N CCN-chem ) and measured values (CDNC) is a further indication of the decreased apparent supersaturation due to high CCN concentration during cloud formation.This process was investigated in more detail using large eddy simulations in Calderón et al. (2022).
To further investigate the feedback of increased CCN concentration on supersaturation, we examined the relationship of the measured cloud droplet concentration (CDNC) and N 100 (number concentration of particles >100 nm) at the SMEAR-IV (Figure S11a in Supporting Information S1) and compared it to an existing data set measured over the North Atlantic (Ramanathan et al., 2001).There is a linear increase in CDNC with N 100 for particle concentrations up to ∼750 cm 3 .For higher N 100 values driven by fire airmass influence, the curve flattens due to the depletion of water vapor.Figure S11b in Supporting Information S1 illustrates the effect of inorganic compounds like sulfate on observed CDNC for this campaign and the existing data sets (McCoy et al., 2018), showing that CDNC observed during the fire episode are notably higher than the previous data.The reason for this can be the differences in meteorological conditions or methodology: in situ measurements at SMEAR-IV define CDNC at the cloud base where activation takes place, while satellite captures CDNC at the cloud top (Klingebiel et al., 2015).
Unfortunately, there are no D act and CDNC data at Zeppelin for the investigated time period due to instrument issues.However, recent study by Freitas et al. (2023) observed high contribution of warm ice nuclei particles (INP) for the same fire episode.Thus, not only liquid clouds but also INP properties can be influenced by LRT aerosol from biomass burning.A long term study of cloud residual number concentrations in Arctic low-level clouds, reported D act for liquid clouds (T > 0°C) in the range of 50-78 nm and inferred a relationship of decreasing D act with decreasing N tot (Karlsson et al., 2021), similar to observations at SMEAR-IV.

Satellite Observations in SMEAR-IV
The effect of the LRT fire aerosols on liquid-cloud properties was further investigated using satellite (MODIS (Terra)) observations at SMEAR-IV.Two case studies were selected during cloud events representing NF (31.10.2020) and fire periods (24.09.2020).During these days, there were no cloud layers above the low-level clouds providing perfect conditions for the analysis of low-level cloud microphysical properties.The histograms for median CDNC retrieved from MODIS for the two case days are shown in Figure 3.The average CDNC increased by a factor of ∼6.8 (from 87 to 555 cm 3 ) for the fire cloud case when compared to that of the NF cloud case.Overall, our results show that the cloud response to elevated aerosol concentrations during fire episode observed with MODIS seems to be consistent with the in situ observations (Table 1) with very good agreement of the derived parameters.

Summary and Conclusions
In this study, we characterized the impact of long-range transported (LRT) fire aerosols from south-eastern Europe on aerosol and cloud properties at two locations.One is in a semi-urban environment in northern

10.1029/2023GL107134
Europe (SMEAR-IV) and the other one is in the high Arctic (Zeppelin) where the background aerosol concentrations are relatively low.The fire episode and representative non-fire (NF) periods were analyzed and the results from both locations were compared.LRT fire aerosols substantially increased the aerosol and CCN concentrations at both locations.Our results suggest that the effect of LRT fire aerosols on aerosol composition and hygroscopicity is driven by the properties of both the LRT fire plumes and the background aerosols.That is, in the high Arctic where marine aerosols are dominating in Autumn and the inorganic fraction of aerosol is relatively high, the hygroscopicity decreases with LRT fire airmass influence, while in the semi-urban northern European location, the opposite is seen due to an increase in the inorganic and oxidized OA fraction during the fire episode.Consequently, the magnitude of increase in CCN concentration during the fire episode is larger at SMEAR-IV than at Zeppelin, suggesting the importance of the hygroscopicity effect for CCN activation under these circumstances.Further, elevated CCN concentration at SMEAR-IV resulted in an increase in cloud activation diameter despite the concurrent increase in hygroscopicity due to the depletion of water vapor during the fire episode.
In situ measurements and satellite observations from MODIS (Terra) at SMEAR-IV showed enhanced CDNC during the fire episode.We found a good agreement between satellite analysis and in situ measurements, when there are no cloud layers above the investigated low-level liquid clouds.The elevated CDNC during LRT fireinfluenced air masses may alter the radiative forcing and cloud albedo (Twomey effect) as well as affect cloud coverage and lifetime.Therefore, we highlight the impact of LRT fire aerosols on CCN and cloud properties particularly at remote locations, where cloud activation can be aerosol-limited.We also point to the need to study (aged) fire emissions in more detail, especially considering the projected increasingly dry conditions in the upcoming decades. in conducting the measurement campaigns at SMEAR IV and Zeppelin Observatory.We also thank Gang Chen (Imperial, UK) for his help with the Zeppelin ACSM data.

Figure 1 .
Figure 1.Overview of (a) mass concentration of Non-Refractory Particulate Matter <1 μm (b) equivalent Black carbon, organic/inorganic mass ratio and (c) size distribution, at SMEAR-IV (left) and Zeppelin (right) for the measurement period.The fire episode is marked with black dashed lines and blue lines indicate the non-fire periods.Note the difference in the scale of the y-axis and color bar for both sites.

Figure 2 .
Figure 2. (a) The mass fraction of aerosol composition for the fire episode and NF periods; (b) average κ chem (κ org = 0.07) and (c) average N CCN-chem for the cloud events during fire and NF periods at SMEAR-IV and Zeppelin.

Figure 3 .
Figure 3. Histograms of CDNC calculated from satellite observations at SMEAR-IV representing a NF (31.10.2020,blue) and a fire period case (24.09.2020, orange).The mean values are indicated.
This work was supported by the European Union's Horizon 2020 research and innovation program under Grant 821205 (FORCeS), and the Knut and Alice Wallenberg (KAW) foundation (WAF project CLOUDFORM, Grant 2017.0165).This work was also supported by the University of Eastern Finland (Doctoral Program in Environmental Physics, Health, and Biology), the Academy of Finland Flagship programme (Grant 337550), and the Research Council of Finland project SHARPCLOUD (Grant 347968) and the Research Council of Finland (project number 339885).

Table 1
Average Values and Standard Deviation of Fraction of Organics ( f org ), κ chem , N CCN-chem and N tot , Cloud Activation Diameter (D act ) and CDNC for Fire and NF Periods at SMEAR-IV and Zeppelin Satellite observations of CDNC are for the case studies on 24.09.2020 and 31.10.2020.