scholarly journals Seasonal variations of aerosol size distributions based on long-term measurements at the high altitude Himalayan site of Nepal Climate Observatory-Pyramid (5079 m), Nepal

2010 ◽  
Vol 10 (21) ◽  
pp. 10679-10690 ◽  
Author(s):  
K. Sellegri ◽  
P. Laj ◽  
H. Venzac ◽  
J. Boulon ◽  
D. Picard ◽  
...  
Keyword(s):  
Seasonal Variability ◽  
Monsoon Season ◽  
Number Concentration ◽  
Residual Layer ◽  
Research Station ◽  
Free Troposphere ◽  
Night Time ◽  
High Accumulation ◽  
Air Masses ◽  
Post Monsoon

Abstract. The present paper investigates the diurnal and seasonal variability of the aerosol total number concentration, number and volume size distribution between 10 nm and 10 μm, from a combination of a scanning mobility particle sizer (SMPS) and an optical counter (OPC), performed over a two-year period (January 2006–February 2008) at the Nepal Climate Observatory-Pyramid (NCO-P) research station, (5079 m a.s.l.). The annual average number concentration measured over the two-year period at the NCO-P is 860 cm−3. Total concentrations show a strong seasonality with maxima during pre-monsoon and post-monsoon seasons and minima during the dry and monsoon seasons. A diurnal variation is also clearly observed, with maxima between 09:00 and 12:00 UTC. The aerosol concentration maxima are mainly due to nucleation processes during the post-monsoon season, as witnessed by high nucleation mode integrated number concentrations, and to transport of high levels of pollution from the plains by valley breezes during the pre-monsoon season, as demonstrated by high accumulation mode integrated number concentrations. Night-time number concentration of particles (from 03:00 to 08:00 NST) are relatively low throughout the year (from 450 cm−3 during the monsoon season to 675 cm−3 during the pre-monsoon season), indicating the of high altitudes background level, as a result of downslope winds during this part of the day. However, it was found that these background concentrations are strongly influenced by the daytime concentrations, as they show the same seasonal variability. If nighttime concentrations were presumed to be representative of free troposphere (FT)/residual layer concentrations, they would be found to be two times higher than at other lower altitudes European sites, such as the Jungfraujoch. However, BL intrusions might contaminate the free troposphere/residual layer even at this altitude, especially during regional air masses influence. Night-time measurements were subsequently selected to study the FT composition according to different air masses, and the effect of long range transport to the station.

scholarly journals Seasonal variations of aerosol size distributions based on long-term measurements at the high altitude Himalayan site of Nepal Climate Observatory-Pyramid (5079 m), Nepal

2010 ◽  
Vol 10 (3) ◽  
pp. 6537-6566 ◽  
Author(s):  
K. Sellegri ◽  
P. Laj ◽  
H. Venzac ◽  
J. Boulon ◽  
D. Picard ◽  
...  
Keyword(s):  
Seasonal Variability ◽  
Monsoon Season ◽  
Number Concentration ◽  
Research Station ◽  
Scanning Mobility Particle Sizer ◽  
Night Time ◽  
High Accumulation ◽  
Post Monsoon ◽  
Post Monsoon Season ◽  
Annual Average Number

Abstract. The present paper investigates the diurnal and seasonal variability of the aerosol total number concentration, number and volume size distribution between 10 nm and 10 μm, from a combination of a scanning mobility particle sizer (SMPS) and an optical counter (OPC), performed over a two-year period (May 2006–May 2008) at the Nepal Climate Observatory-Pyramid (NCO-P) research station, (5079 m a.s.l.). The annual average number concentration measured over the two-year period at the NCO-P is 860 cm−3. Total concentrations show a strong seasonality with maxima during pre-monsoon and post-monsoon seasons and minima during the dry and monsoon seasons. A diurnal variation is also clearly observed, with maxima between 09:00 and 12:00 UTC. The aerosol concentration maxima are mainly due to nucleation processes during the post-monsoon season, as witnessed by high nucleation mode integrated number concentrations, and to transport of high levels of pollution from the plains by valley breezes during the pre-monsoon season, as demonstrated by high accumulation mode integrated number concentrations. Night-time number concentration of particles (from 03:00 to 08:00 NST) are relatively low throughout the year (from 450 cm−3 during the monsoon season to 675 cm−3 during the pre-monsoon season), indicating the level of free_tropospheric background, as a result of downslope winds during this part of the day. However, it was found that these background concentrations are strongly influenced by the daytime concentrations, as they show the same seasonal variability. The resulting free troposphere (FT)/residual layer concentrations are found to be two times higher than at other lower altitudes European sites, such as the Jungfraujoch. Night-time measurements were subsequently selected to study the FT composition according to different air masses, and the effect of long range transport to the station.

scholarly journals Seasonal variation of aerosol size distributions in the free troposphere and residual layer at the puy de Dôme station, France

2009 ◽  
Vol 9 (4) ◽  
pp. 1465-1478 ◽  
Author(s):  
H. Venzac ◽  
K. Sellegri ◽  
P. Villani ◽  
D. Picard ◽  
P. Laj
Keyword(s):  
Boundary Layer ◽  
Seasonal Variation ◽  
Size Distribution ◽  
Seasonal Variability ◽  
Number Concentration ◽  
Residual Layer ◽  
Size Distributions ◽  
Free Troposphere ◽  
Air Mass ◽  
Aerosol Sources

Abstract. Particle number concentration and size distribution are important variables needed to constrain the role of atmospheric particles in the Earth radiation budget, both directly and indirectly through CCN activation. They are also linked to regulated variables such as particle mass (PM) and therefore of interest to air quality studies. However, data on their long-term variability are scarce, in particular at high altitudes. In this paper, we investigate the diurnal and seasonal variability of the aerosol total number concentration and size distribution at the puy de Dôme research station (France, 1465 m a.s.l.). We report a variability of aerosol particle total number concentration measured over a five-year (2003–2007) period for particles larger than 10 nm and aerosol size distributions between 10 and 500 nm over a two-year period (January 2006 to December 2007). Concentrations show a strong seasonality with maxima during summer and minima during winter. A diurnal variation is also observed with maxima between 12:00 and 18:00 UTC. At night (00:00–06:00 UTC), the median hourly total concentration varies from 600 to 800 cm−3 during winter and from 1700 to 2200 cm−3 during summer. During the day (08:00–18:00 UTC), the concentration is in the range of 700 to 1400 cm−3 during winter and of 2500 to 3500 cm−3 during summer. An averaged size distribution of particles (10–500 nm) was calculated for each season. The total aerosol number concentrations are dominated by the Aitken mode integral concentrations, which drive most of the winter to summer total concentrations increase. The night to day increase in dominated by the nucleation mode integral number concentration. Because the site is located in the free troposphere only a fraction of the time, in particular at night and during the winter season, we have subsequently analyzed the variability for nighttime and free tropospheric (FT)/residual layer (RL) conditions only. We show that a seasonal variability is still observed for these FT/RL conditions. The FT/RL seasonal variation is due to both seasonal changes in the air mass origin from winter to summer and enhanced concentrations of particles in the residual layer/free troposphere in summer. The later observation can be explained by higher emissions intensity in the boundary layer, stronger exchanges between the boundary layer and the free troposphere as well as enhanced photochemical processes. Finally, aerosols mean size distributions are calculated for a given air mass type (marine/continental/regional) according to the season for the specific conditions of the residual layer/free troposphere. The seasonal variability in aerosol sources seems to be predominant over the continent compared to the seasonal variation of marine aerosol sources. These results are of regional relevance and can be used to constrain chemical-transport models over Western Europe.

scholarly journals A statistical analysis of North East Atlantic (submicron) aerosol size distributions

2011 ◽  
Vol 11 (8) ◽  
pp. 21677-21711 ◽  
Author(s):  
M. Dall'Osto ◽  
C. Monahan ◽  
R. Greaney ◽  
D. C. S. Beddows ◽  
R. M. Harrison ◽  
...  
Keyword(s):  
Number Concentration ◽  
Open Ocean ◽  
Research Station ◽  
Marine Biota ◽  
Size Distributions ◽  
East Atlantic ◽  
Air Masses ◽  
North East ◽  
Data Coverage ◽  
Aitken Mode

Abstract. The Global Atmospheric Watch research station at Mace Head (Ireland) offers the possibility to sample some of the cleanest air masses being imported into Europe as well as some of the most polluted being exported out of Europe. We present a statistical Cluster~analysis of the physical characteristics of aerosol size distributions in air ranging from the cleanest to the most polluted for the year 2008. Data coverage achieved was 75 % throughout the year. By applying the Hartigan-Wong k-Means method, 12 Clusters were identified as systematically occurring and these 12 Clusters could be further combined into 4 categories with similar characteristics, namely: coastal nucleation category (occurring 21.3 % of the time), open ocean nucleation category (occurring 32.6 % of the time), background clean marine category (occurring 26.1 % of the time) and anthropogenic category (occurring 20 % of the time) aerosol size distributions. The coastal nucleation category is characterised by a clear and dominant nucleation mode at sizes less that 10 nm while the open ocean nucleation category is characterised by a dominant Aitken mode between 15 nm and 50 nm. The background clean marine characteristic is a clear bimodality in the size distribution, although it should be noted that either the Aitken mode or the Accumulation mode may dominate the number concentration. By contrast, the continentally-influenced size distributions are generally more mono-modal, albeit with traces of bi-modality. The open ocean category occurs more often during May, June and July, corresponding with the N. E. Atlantic high biological period. Combined with the relatively high percentage frequency of occurrence (32.6 %), this suggests that the marine biota is an important source of new aerosol particles in N. E. Atlantic Air.

scholarly journals Week Day and Week End Air Ion Variability at Rural station Ramanandnagar (17° 4’ N 74° 25’E), India and At Different Atmospheric Sites in India

2013 ◽  
Vol 13 (1) ◽  
pp. 65-73
Keyword(s):  
Urban Areas ◽  
Transition Period ◽  
Monsoon Season ◽  
Pollution Index ◽  
Negative Ion ◽  
Rural Station ◽  
Night Time ◽  
Post Monsoon ◽  
Post Monsoon Season ◽  
The Government

Globalization and liberalization polices of the government of India have increased the number of road vehicles nearly 92.6% from 1980-81 to 2003-2004. Therefore to know whether there is effect of increase of industrialization in the urban areas like Pune (18° 32′N, 73° 51′E); Mumbai (18° 55' N, 72° 54' E) and at rural station like Ramanandnagar (17° 4′ N, 74° 25′ E); pollution index is measured. Pollution index which is ratio of average positive to negative small air ion ratio is plotted for week days and week end. At the rural station like Ramanandnagar Monday to Saturday are working days, while Sunday is holiday. It is observed that ratio of average positive to negative small ion ratio is maximum for all time periods during the week day as compared to week end. The data have been collected during the period from first 1 June 2007 to 31 May 2008; the period under analysis involves 8,040 hours shows that the peak of the positive to negative small air ion ratio is observed in winter, and dip is observed in post-monsoon season. As Ramanandnagar is surrounded by vegetation area, therefore due to plant transpiration of Radon and Thoron small air ion maximum are observed at noon time rather than night time. During the week end positive small air ion count is low as compared to week days. While during week end negative small air ion count is very high as compared to week days, which is observed in all the seasons. Post-monsoon is the transition period during which few thunder storms are observed. Due to these thunder storms additional amount negative ion are introduced and positively charged aerosols are cleared from the atmosphere. Therefore in the post-monsoon negative small air ion count is high as compared to all other seasons. Such type of diurnal variation of small air ion detected at rural station Ramanandnagar has never been observed elsewhere.

scholarly journals Vertical profiles of optical and microphysical particle properties above the northern Indian Ocean during CARDEX 2012

2015 ◽  
Vol 15 (3) ◽  
pp. 3907-3953 ◽  
Author(s):  
F. Höpner ◽  
F. A.-M. Bender ◽  
A. M. L. Ekman ◽  
P. S. Praveen ◽  
C. Bosch ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Bay Of Bengal ◽  
Monsoon Season ◽  
Number Concentration ◽  
Northern Indian Ocean ◽  
Gangetic Plain ◽  
Air Masses ◽  
Particle Absorption ◽  
Aerosol Number Concentration

Abstract. A detailed analysis of optical and microphysical properties of aerosol particles during the dry winter monsoon season above the northern Indian Ocean is presented. The Cloud Aerosol Radiative Forcing Experiment (CARDEX), conducted in February and March 2012 at the Maldives Climate Observatory on Hanimaadhoo island (MCOH) in the Republic of the Maldives, used autonomous unmanned aerial vehicles (AUAV) to perform vertical in-situ measurements of particle number concentration, particle number size distribution as well as particle absorption. These measurements were used together with surface-based Mini Micro Pulse Lidar (MiniMPL) observations and aerosol in-situ and off-line measurements to investigate the vertical distribution of aerosol particles. Air masses were mainly advected over the Indian subcontinent and the Arabian Peninsula. Mean surface aerosol number concentration was 1717±604 cm−3 and the highest values were found in air masses from the Bay of Bengal and Indo–Gangetic Plain (2247±370 cm−3). Investigations of the free tropospheric air showed that elevated aerosol layers with up to 3 times higher aerosol number concentrations than at the surface occurred mainly during periods with air masses originating from the Bay of Bengal and the Indo–Gangetic Plain. Compared to the Indian Ocean Experiment (INDOEX) conducted in winter 1999, elevated aerosol layers with increased aerosol number concentration were observed more frequently in 2012. However, lower particle absorption at the surface (σabs(520 nm)=8.5±4.2 Wm−1) was found during CARDEX compared to INDOEX 1999. By combining vertical in-situ measured particle absorption with scattering calculated with Mie-theory, layers with single-scattering albedo (SSA) values of specific source regions were derived and utilized to calculate vertical particle absorption profiles from MiniMPL profiles. SSA surface values for dry conditions were found to be 0.94±0.02 and 0.91±0.02 for air masses from the Arabian Sea (and Middle East countries) and India (and Bay of Bengal), respectively. Lidar-derived particle absorption profiles showed both a similar magnitude and structure as the in-situ profiles measured with the AUAV. However, primarily due to insufficient accuracy in the SSA estimates, the lidar-derived absorption profiles have large uncertainties and are generally weakly correlated to vertically in-situ measured particle absorption. Furthermore, the mass absorption efficiency (MAE) for the northern Indian Ocean during the dry monsoon season was calculated to determine equivalent black carbon (EBC) concentrations from particle absorption measurements. A mean MAE of 11.6 and 6.9 m2 g−1 for 520 and 880 nm, respectively, was found, likely representing internally mixed BC containing particles. Lower MAE values for 880 nm were found for air masses originating from dust regions such as the Arabian Peninsula and western Asia (5.6 m2 g−1) or from closer source regions as southern India (4.3m2 g−1).

scholarly journals Detecting moisture transport pathways to the subtropical North Atlantic free troposphere using paired H<sub>2</sub>O-<i>δ</i>D in situ measurements

2016 ◽  
Vol 16 (7) ◽  
pp. 4251-4269 ◽  
Author(s):  
Yenny González ◽  
Matthias Schneider ◽  
Christoph Dyroff ◽  
Sergio Rodríguez ◽  
Emanuel Christner ◽  
...  
Keyword(s):  
North Atlantic ◽  
In Situ Measurements ◽  
Back Trajectory ◽  
Free Troposphere ◽  
Night Time ◽  
Humid Air ◽  
Transport Pathways ◽  
Air Masses ◽  
Dry Convection

Abstract. We present two years of in situ measurements of water vapour (H2O) and its isotopologue ratio (δD, the standardized ratio between H216O and HD16O), made at two remote mountain sites on Tenerife in the subtropical North Atlantic. We show that the data – if measured during night-time – are well representative for the lower/middle free troposphere. We use the measured H2O-δD pairs, together with dust measurements and back trajectory modelling for analysing the moisture pathways to this region. We can identify four principally different transport pathways. The air mass transport from high altitudes and high latitudes shows two different scenarios. The first scenario brings dry air masses to the stations, as the result of condensation events occurring at low temperatures. The second scenario brings humid air masses to the stations, due to cross-isentropic mixing with lower-level and more humid air during transport since last condensation (LC). The third pathway is transportation from lower latitudes and lower altitudes, whereby we can identify rain re-evaporation as an occasional source of moisture. The fourth pathway is linked to the African continent, where during summer, dry convection processes over the Sahara very effectively inject humidity from the boundary layer to higher altitudes. This so-called Saharan Air Layer (SAL) is then advected westward over the Atlantic and contributes to moisten the free troposphere. We demonstrate that the different pathways leave distinct fingerprints on the measured H2O-δD pairs.

scholarly journals Seasonal variability of measured ozone production efficiencies in the lower free troposphere of Central Europe

2007 ◽  
Vol 7 (1) ◽  
pp. 223-236 ◽  
Author(s):  
P. Zanis ◽  
A. Ganser ◽  
C. Zellweger ◽  
S. Henne ◽  
M. Steinbacher ◽  
...  
Keyword(s):  
Seasonal Variation ◽  
Central Europe ◽  
Seasonal Variability ◽  
Transition Period ◽  
Ozone Production ◽  
Data Series ◽  
Research Station ◽  
Monthly Means ◽  
Free Troposphere ◽  
Production Efficiencies

Abstract. In this study we present the seasonal variability of ozone production efficiencies (EN), defined as the net number of ozone molecules produced per molecule of nitrogen oxides (nitrogen oxide (NO) + nitrogen dioxide (NO2)=NOx) oxidized to NOz (total reactive nitrogen (NOy)–NOx) determined from field measurements of a seven-year period (1998–2004) at the Swiss high-alpine research station Jungfraujoch (JFJ), 3580 m a.s.l. This dataset is a unique long-term data series of nitrogen levels in the free troposphere over Central Europe and hence it offers an excellent opportunity to perform such an analysis and provide further evidence to the photochemical origin of the ozone spring maximum at locations of the northern hemisphere distant from nearby pollution sources. Experimentally derived daily EN values have been selected for 571 days out of the 2557 days from 1998 to 2004, from which an average ozone production efficiency of 18.8±1.3 molecules of O3 produced per molecule of NOx oxidized was calculated. This value indicates the great potential and importance of photochemical ozone production in the free troposphere. The monthly means of experimentally derived daily EN values show a seasonal variation with lower values from May to August, which can be probably attributed to more efficient vertical transport of polluted air masses from the atmospheric boundary layer up to JFJ. In agreement, theoretically derived monthly EN values show similar seasonal variation. The ratio NOy/CO, a parameter to assess the aging process that has occurred in an air parcel, was used as a criterion to disaggregate the 571 selected days between undisturbed and disturbed free tropospheric (FT). The monthly means of experimentally derived EN values for the undisturbed FT conditions show a distinct seasonal cycle with higher values in the cold season from November to April. The EN values for undisturbed FT conditions are particularly higher than the respective monthly EN values for disturbed FT conditions from February to October. It should be noted that the monthly EN values of March (EN=35.8) and April (EN=34.9) are among the highest values throughout the year for undisturbed FT conditions at JFJ. These results highlight the key and possibly the dominant role for photochemistry in the observed build-up of tropospheric ozone in the winter-spring transition period.

scholarly journals Abundance and distribution of gaseous ammonia and particulate ammonium at Delhi, India

2012 ◽  
Vol 9 (12) ◽  
pp. 5023-5029 ◽  
Author(s):  
S. Singh ◽  
U. C. Kulshrestha
Keyword(s):  
Monsoon Season ◽  
Gaseous Ammonia ◽  
Atmospheric Conditions ◽  
Night Time ◽  
Total N ◽  
Post Monsoon ◽  
Nh3 Emission ◽  
Rural Sites ◽  
Abundance And Distribution ◽  
Urban Sites

Abstract. This study reports abundance and distribution of gaseous NH3 and particulate NH4&amp;plus; at Delhi. Gaseous NH3 and particulate NH4&amp;plus; concentrations were measured during pre-monsoon, monsoon and post-monsoon seasons of the years 2010 and 2011. Average concentrations of gaseous NH3 during pre-monsoon, monsoon and post-monsoon seasons were recorded as 26.4, 33.2 and 32.5 μg m−3, respectively. Gaseous NH3 concentrations were the highest during monsoon, thought to be due to decay and decomposition of plants and other biogenic material under wet conditions, leading to increased NH3 emission. The results showed that particulate NH4&amp;plus; was always lower than the gaseous NH3 during all the seasons. The concentrations of particulate NH4&amp;plus; were recorded as 11.6, 22.9 and 8.5 μg m−3 during pre-monsoon, monsoon and post-monsoon seasons, respectively. The percent fraction of particulate NH4&amp;plus; was noticed to be highest during the monsoon season, which is attributed to increased humidity levels favouring partitioning into the aerosol phase. On an average, 33.3% of total N-NHx was present as particulate NH4&amp;plus;. Higher concentrations of NH3 noticed during night time may be due to stable atmospheric conditions. The study highlighted that, as compared with rural sites, urban sites showed higher concentrations of gaseous NH3 in India, which may be due to higher population density, human activities and poor sanitation arrangements.

scholarly journals Seasonal variability of measured Ozone production efficiencies in the lower free troposphere of Central Europe

2006 ◽  
Vol 6 (5) ◽  
pp. 9315-9349 ◽  
Author(s):  
P. Zanis ◽  
A. Ganser ◽  
C. Zellweger ◽  
S. Henne ◽  
M. Steinbacher ◽  
...  
Keyword(s):  
Seasonal Variation ◽  
Central Europe ◽  
Seasonal Variability ◽  
Transition Period ◽  
Ozone Production ◽  
Data Series ◽  
Research Station ◽  
Monthly Means ◽  
Free Troposphere ◽  
Production Efficiencies

Abstract. In this study we present the seasonal variability of ozone production efficiencies (EN), defined as the net number of ozone molecules produced per molecule of nitrogen oxides (nitrogen oxide (NO) + nitrogen dioxide (NO2)=NOx) oxidized to NOz (total reactive nitrogen (NOy)-NOx) for a seven-year period (1998–2004) at the Swiss high-alpine research station Jungfraujoch (JFJ), 3580 m a.s.l. This dataset is a unique long-term data series of nitrogen levels in the free troposphere over Central Europe and hence it offers an excellent opportunity to perform such an analysis and provide further evidence to the photochemical origin of the ozone spring maximum at locations of the northern hemisphere distant from nearby pollution sources. Experimentally derived daily EN values have been selected for 571 days out of the 2557 days from 1998 to 2004, from which an average ozone production efficiency of 18.8±1.3 molecules of O3 produced per molecule of NOx oxidized was calculated. This value indicates the great potential and importance of photochemical ozone production in the free troposphere. The monthly means of experimentally derived daily EN values show a seasonal variation with lower values from May to August, which can be probably attributed to more efficient vertical transport of polluted air masses from the atmospheric boundary layer up to JFJ. In agreement, theoretically derived monthly EN values show similar seasonal variation. The ratio NOy/CO, a parameter to assess the aging process that has occurred in an air parcel, was used as a criterion to disaggregate the 571 selected days between undisturbed and disturbed free tropospheric (FT). The monthly means of experimentally derived EN values for the undisturbed FT conditions show a distinct seasonal cycle with higher values in the cold season from November to April. The EN values for undisturbed FT conditions are particularly higher than the respective monthly EN values for disturbed FT conditions from February to October. It should be noted that the monthly EN values of March (EN=35.8) and April (EN=34.9) are among the highest values throughout the year for undisturbed FT conditions at JFJ. These results highlight the key and possibly the dominant role for photochemistry in the observed build-up of tropospheric ozone in the winter-spring transition period.

scholarly journals Long term particle size distribution measurements at Mount Waliguan, a high-altitude site in inland China

2009 ◽  
Vol 9 (1) ◽  
pp. 2049-2079
Author(s):  
N. Kivekäs ◽  
J. Sun ◽  
M. Zhan ◽  
V.-M. Kerminen ◽  
A. Hyvärinen ◽  
...  
Keyword(s):  
Particle Concentration ◽  
Particle Number ◽  
Anthropogenic Pollution ◽  
Number Concentration ◽  
Average Particle ◽  
Ambient Conditions ◽  
Night Time ◽  
Air Masses ◽  
Nucleation Mode ◽  
Aitken Mode

Abstract. Particle number size distributions in size range 12–570nm were measured continuously at Mount Waliguan, a remote mountain-top station in inland China. The station is located at the altitude of 3816 m above the sea level, and some 600 m above the surrounding area. The measurement period lasted from September 2005 to May 2007. The measurements were verified with independent CPC measurements at the same site. The average particle concentration in ambient conditions was 2040 cm−3, which is higher than the values measured at similar altitude in other regions of the world. On average, the Aitken mode contributed to roughly half of the particle number concentration. The concentrations were found to be higher during the summer than during the winter. The diurnal variation was also investigated and a clear pattern was found for the nucleation mode during all seasons, so that the nucleation mode particle concentration increased in the afternoon. The same pattern was visible in the Aitken mode during the summer, whereas the accumulation mode did not show any level of diurnal pattern. Excluding the nucleation mode, the average day-time particle concentrations were not significantly higher than those measured at night-time, indicating no systematic pattern of change between planetary boundary layer conditions and free troposphere conditions. In air masses coming from east, the number concentration of particles was higher than in other air masses, which indicates that the air mass might be affected by anthropogenic pollution east of the station. Also other factors, such as active new-particle formation, keep aerosol number concentrations high in the area.

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