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Continuous measurements of submicron particle size distribution at boreal forest station in southern Finland
Pergamon
J. Aerosol Sci. Vol. 28, Suppl. 1, pp. $403--$404, 1997 ©1997 Elsevier Science Ltd. All fights reserved Printed in Great Britain
PII:SO021-8502(97)O0248-6
0021-8502/97 $17.00+0.00
Continuous Measurements of Submicron Particle Size Distribution at Boreal Forest Station in Southern Finland J.M.M/ikel~i 1, M. Kulmala 1, P. Aalto 1, A. Toivonen 1, T. Pohja 2 1 Department of Physics, P.O.Box 9 FIN-00014 University of Helsinki, FINLAND 2 SMEAR Station, Hyyti~il~i FIN-35500 Korkeakoski, FINLAND
Keywords Atmospheric aerosols, Aerosol formation, Growth, Size distributions Size distribution measurement of ambient submicron (particle diameter Dp below 1 #m) and ultrafine particles (Dp < 20 nm) is usually carried out in measurement campaigns. There is a lack of regular data, on the submicron aerosol particles. Recently the new particle production in the atmosphere has received growing experimental interest. If the particle formation events are probable, but occurring rarely in time, then apparently relatively longer monitoring period with the state-of-art instrumentation is needed. We have measured submicron particles rather continuously since January 31st 1996 at a forest site in Southern Finland. Number size distribution data from the size range of 3-500 nm (particle diameter) are obtained every 10 minutes using two DMPS systems running simultaneously (M~ikel~ et al., 1997). The measurements are carried out inside forest, and there are no local sources of pollution nearby of the site. The boreal forest measurement station 'SMEAR II' at Hyyti£1£ is located in southern Finland (61 51'N, 24 17'E, 170 m asl) (see SMEAR-homepage, 1997). In the data, the already established 3-modal structure of submicron particles was clearly observed, confirming the pattern observed and discussed by Covert et al. (1996). Not all of these three modes are continuously present. During cloudy periods, usually only Aitken and accumulation modes are present, the respective mean sizes being 40-70 nm and 150-250 nm at our forest site in Southern Finland. To characterize the days in which the events of new particle formation were seen, we show one diagram as a mesh plot of April 13th in Figure 1. On April 13th the size growth of the nucleation mode during afternoon is apparent. In most cases when new particle formation is observed, the nucleation peak at 5-6 nm can be seen to appear before noon and both particle size and number concentration are seen to increase. During the sunny days when new particle formation events were observed, a flip-over
S403
$404
Abstracts of the 1997EuropeanAerosolConference Hyyti&l& 13-4-1996
"~
2
2.5
Log(Particle Diameter [nm])
Figure 1: A day with a particle formation event (April 13th, 1996). in the vertical temperature profile was usually also detected. The change from stable situation at night to mixing in the morning occurred at 8-9 a.m. This suggests that the actual particle formation process was also accompanied with vertical transport of air masses. We cannot completely exclude the possibility that the particles were not actually nucleated at the altitude of our measurements, but, instead, were formed higher up and mixed to the surface very shortly thereafter. The overall data looks promising and it clearly shows benefits of continuous monitoring of the submicron aerosol particle size distribution over arbitrary case studies. The measurements will be continued. References Covert, D.S., Wiedensohler, A., Aalto, P., Heinzenberg, J., McMurry, P.H. and Leck, C. (1996) Aerosol number size distributions from 3 to 500 nm diameter in the arctic marine boundary layer during summer and autumn. TELLUS 48B, 197-212. M£kel~i, J.M., Aalto, P., Jokinen, V. Pohja, T., Nissinen, A. Palmroth, S., Markkanen, T., Seitsonen, K. Lihavainen, H. and Kulmala, M. (1997) Observations of ultrafine aerosol particle formation and growth in boreal forest. Geophysics Research Letters (Accepted). SMEAR Homepage, Internet, "http://honeybee.helsinki.fi/HYYTIALA/smear"
J. Aerosol Sci. Vol. 28, Suppl. 1, pp. $403--$404, 1997 ©1997 Elsevier Science Ltd. All fights reserved Printed in Great Britain
PII:SO021-8502(97)O0248-6
0021-8502/97 $17.00+0.00
Continuous Measurements of Submicron Particle Size Distribution at Boreal Forest Station in Southern Finland J.M.M/ikel~i 1, M. Kulmala 1, P. Aalto 1, A. Toivonen 1, T. Pohja 2 1 Department of Physics, P.O.Box 9 FIN-00014 University of Helsinki, FINLAND 2 SMEAR Station, Hyyti~il~i FIN-35500 Korkeakoski, FINLAND
Keywords Atmospheric aerosols, Aerosol formation, Growth, Size distributions Size distribution measurement of ambient submicron (particle diameter Dp below 1 #m) and ultrafine particles (Dp < 20 nm) is usually carried out in measurement campaigns. There is a lack of regular data, on the submicron aerosol particles. Recently the new particle production in the atmosphere has received growing experimental interest. If the particle formation events are probable, but occurring rarely in time, then apparently relatively longer monitoring period with the state-of-art instrumentation is needed. We have measured submicron particles rather continuously since January 31st 1996 at a forest site in Southern Finland. Number size distribution data from the size range of 3-500 nm (particle diameter) are obtained every 10 minutes using two DMPS systems running simultaneously (M~ikel~ et al., 1997). The measurements are carried out inside forest, and there are no local sources of pollution nearby of the site. The boreal forest measurement station 'SMEAR II' at Hyyti£1£ is located in southern Finland (61 51'N, 24 17'E, 170 m asl) (see SMEAR-homepage, 1997). In the data, the already established 3-modal structure of submicron particles was clearly observed, confirming the pattern observed and discussed by Covert et al. (1996). Not all of these three modes are continuously present. During cloudy periods, usually only Aitken and accumulation modes are present, the respective mean sizes being 40-70 nm and 150-250 nm at our forest site in Southern Finland. To characterize the days in which the events of new particle formation were seen, we show one diagram as a mesh plot of April 13th in Figure 1. On April 13th the size growth of the nucleation mode during afternoon is apparent. In most cases when new particle formation is observed, the nucleation peak at 5-6 nm can be seen to appear before noon and both particle size and number concentration are seen to increase. During the sunny days when new particle formation events were observed, a flip-over
S403
$404
Abstracts of the 1997EuropeanAerosolConference Hyyti&l& 13-4-1996
"~
2
2.5
Log(Particle Diameter [nm])
Figure 1: A day with a particle formation event (April 13th, 1996). in the vertical temperature profile was usually also detected. The change from stable situation at night to mixing in the morning occurred at 8-9 a.m. This suggests that the actual particle formation process was also accompanied with vertical transport of air masses. We cannot completely exclude the possibility that the particles were not actually nucleated at the altitude of our measurements, but, instead, were formed higher up and mixed to the surface very shortly thereafter. The overall data looks promising and it clearly shows benefits of continuous monitoring of the submicron aerosol particle size distribution over arbitrary case studies. The measurements will be continued. References Covert, D.S., Wiedensohler, A., Aalto, P., Heinzenberg, J., McMurry, P.H. and Leck, C. (1996) Aerosol number size distributions from 3 to 500 nm diameter in the arctic marine boundary layer during summer and autumn. TELLUS 48B, 197-212. M£kel~i, J.M., Aalto, P., Jokinen, V. Pohja, T., Nissinen, A. Palmroth, S., Markkanen, T., Seitsonen, K. Lihavainen, H. and Kulmala, M. (1997) Observations of ultrafine aerosol particle formation and growth in boreal forest. Geophysics Research Letters (Accepted). SMEAR Homepage, Internet, "http://honeybee.helsinki.fi/HYYTIALA/smear"