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Extensive continuous particle number size distribution measurements took place during two summers (2020 and 2021) at 11 sites in Greece for the investigation of the frequency and the spatial extent of new particle formation (NPF). The study area is characterized by high solar intensity and fast photochemistry and has moderate to low fine particulate matter levels during the summer. The average PM 2.5 levels were relatively uniform across the examined sites. The NPF frequency during summer varied from close to zero in the southwestern parts of Greece to more than 60 % in the northern, central, and eastern regions. The mean particle growth rate for each station varied between 3.4 and 8 nm h -1 , with an average rate of 5.7 nm h -1. At most of the sites there was no statistical difference in the condensation sink between NPF event and non-event days, while lower relative humidity was observed during the events. The high-NPF-frequency sites in the north and northeast were in close proximity to both coal-fired power plants (high emissions of SO 2) and agricultural areas with some of the highest ammonia emissions in the country. The southern and western parts of Greece, where NPF was infrequent, were characterized by low ammonia emissions, while moderate levels of sulfuric acid were estimated (10 7 molec. cm -3) in the west. Although the emissions of biogenic volatile organic compounds were higher in western and southern sectors, they did not appear to lead to enhanced frequency of NPF. The infrequent events at these sites occurred when the air masses had spent a few hours over areas with agricultural activities and thus elevated ammonia emissions. Air masses arriving at the sites directly from the sea were not connected with atmospheric NPF. These results support the hypothesis that ammonia and/or amines limit new particle formation in the study area. [ABSTRACT FROM AUTHOR]

Extensive continuous particle number size distribution measurements took place during two summers (2020 and 2021) in 11 sites in Greece for the investigation of the frequency and the spatial extent of new particle formation (NPF). The study area is characterized by high solar intensity, fast photochemistry, and has moderate to low fine particulate matter levels during the summer. The average PM2.5 levels were relatively uniform across the examined sites. The NPF frequency during summer varied from close to zero in the southwestern parts of Greece to more than 60 % in the northern, central, and eastern regions. The mean particle growth rate for each station varied between 3.4 and 8 nm h-1, with an average rate of 5.7 nm h-1. In most of the sites there was no statistical difference in the condensation sink between NPF event and non-event days, while lower relative humidity was observed during the events. The high NPF frequency sites in the north and northeast were in close proximity to both coal-fired power plants (high emissions of SO2) and to agricultural areas with some of the highest ammonia emissions in the country. The southern and western parts of Greece, where NPF was infrequent, were characterized by low ammonia emissions, while moderate levels of sulfuric acid were estimated (107 molecules cm-3) in the west. Although the emissions of biogenic volatile organic compounds were higher in western and southern sectors, they did not appear to lead to enhanced frequency of NPF. The infrequent events in these sites occurred when the air masses had spent a few hours over areas with agricultural activities, and thus elevated ammonia emissions. Air masses arriving at the sites directly from the sea were not connected with atmospheric nucleation. These results support the hypothesis that ammonia and/or amines are limiting new particle formation in the study area. [ABSTRACT FROM AUTHOR]

Two field campaigns were conducted in Patras during the summers of 2020 and 2021 in order to quantify the nucleation frequency in this area. Out of the 120 days with available measurements only 15 (12%) new particle formation events occurred. This low frequency is surprising given the high sunlight intensity, sulfur availability and low particle matter levels in the area during the study period. On the other hand, nucleation mode particles with average diameters of 20–40 nm appeared during the afternoon on 31% of the days. These particles did not grow, and the initial stages of their formation could not be observed. The corresponding days are traditionally classified as undefined events in similar studies. Our analysis suggests that these nucleation mode particles were not associated with emissions close to the measurement site but rather they had been formed several hours earlier in an area 100–150 km northeast of the field site and had grown significantly by the time they reached Patras. The air mass history suggested that new particle formation often took place in the vicinity of an area with significant agricultural activity and therefore high emissions of ammonia and amines. The term "transported events" can be used to better characterize these observed undefined days. The relatively high emissions of biogenic volatile organic compounds in western Greece, where Patras is located, did not appear to assist in the local formation of new particles. • Infrequent summertime nucleation in a sunny Mediterranean area. • Frequent formation of particles 100 km away from the site and transport. • Evidence that ammonia or amines are involved in new particle formation. • Importance of agricultural activities in NPF. • Biogenic volatile organic compounds do not dominate NPF in this area. [ABSTRACT FROM AUTHOR]