ANALYSIS OF NEW PARTICLE FORMATION EVENTS FROM FOUR YEARS
OF CONTINUOUS MEASUREMENTS IN INDIAN HIMALAYAS
E. ASMI1 , K. NEITOLA1 , A.-P. HYVÄRINEN1 , M. KOMPPULA2 , H. LIHAVAINEN1 , V.P.
SHARMA3 , T.S. PANWAR3 , V.-M. KERMINEN1 , and Y. VIISANEN1
1
Climate Change, Finnish Meteorological Institute, Helsinki, Finland.
2
Kuopio Unit, Atmospheric Research, Finnish Meteorological Institute, Kuopio, Finland.
3
Energy Environment Policy Division, Energy and Resources Institute, New Delhi, India.
Keywords: nucleation, particle formation and growth, long-term measurements, background
aerosol.
INTRODUCTION
New particle formation is an important source of atmospheric particles and has been shown to
take frequently place troughout the world (Kulmala et al., 2004). Characteristics of the particle
formation, such as particle formation and growth rates, depend on the availability of the nucleating
and condensing vapours. They are of importance for global models to account for the effects
of secondary particle formation on the total aerosol budget and further, to estimate the aerosol
climatic impacts.
Long-term measurements have proven to be useful for quantifying aerosol properties, processes and
their connections with the climate. In this study, we present particle formation characteristics at
previously rarely studied background area in India. Over four years of continuous size distribution
data are used in the analysis.
METHODS
The measurement site Mukteshwar in India (29o 26’N, 79o 37’E), is located about 350 km northeast
of New Delhi and represents an areal background. The site is at 2180 m altitude in a rural region
at the Himalaya mountains. Detailed desription of the site is presented e.g. by (Hyvärinen et al.,
2009).
Particle number size distributions were measured with a Differential Mobility Particle Sizer (DMPS)
in a size range 10–800 nm. The specifics of the measurements are explained in (Komppula et al.,
2009). The measurements started on 26 November, 2005 and are yet ongoing. The last day included
in the present analysis was 23 January, 2010.
The days were classified into event days, separated into class I and II events, non-event days and
undefined days according to the methods described by (Dal Maso et al., 2005). Not classifiable
days contained those of missing or bad data. For event I days, particle growth and formation rates
were further calculated. In continuation of the analysis the obtained results will be coupled with
the measured meteorological parameters and air mass origin. Factors, promoting and limiting the
particle formation at the site, are pursued to be identified.
CONCLUSIONS
Seasonal cycle of the particle formation is highly pronounced and shows a distinct maximum during
spring and early summer months from March until June (Fig. 1). The events are most frequent in
April when on 64 % of the classified days an event was observed. This result is well in line with
the particle modal characteristics and the nucleation mode concentrations at the site, presented
previously by (Komppula et al., 2009).
Event to non−events days [%]
70
60
50
40
30
20
10
0
1
2
3
4
5
6
7
8
Month
9
10
11
12
Figure 1: Seasonality of the observed new particle formation events averaged from the data of the
whole measurement period. The event to non-event ratio as a function of the month is presented.
Note that unclassified and undentified days are not included.
An example of an event, characterised by a strong particle formation (J10 = 1.8 cm−3 s−1 ) and a
relatively slow growth rate of 1.5 nm h−1 , is presented in Figure 2. Overall, the particle growth rate
varied between 1.5 and 5.5 nm h−1 , with an average value of 2.9 nm h−1 . These growth rates are
in agreement with corresponding values from other background sites (Kulmala et al., 2004). The
average condensation sink (see e.g. (Dal Maso et al., 2005)) in the beginning of the events (class I)
was 8.4e−3 s−1 while the average sink for the whole formation period (months May to June) was
13.2e−3 s−1 . This suggests that the decrease of the background aerosol concentration, and thereby
deminished sink for the condensing vapours and for the initial nucleated particles, was one of the
factors promoting new particle formation.
ACKNOWLEDGEMENTS
This work was supported by the Ministry of Foreign Affairs of Finland and by the Academy of
Finland Centre of Excellence program (project no 1118615). The authors would like to acknowledge
Timo Anttila for technical assistance in planning and during the site visits and D. S. Rawat for
valuable routine upkeeping of the instruments.
DMPS Mukteshwar India
−6
Diameter [m]
10
−7
10
00:00
06:00
12:00
18:00
24:00
3
Concentration [1/cm3]
dN/dlog(Dp) [1/cm ]
10
15000
100
1000
10000
10000
5000
0
00:00
06:00
12:00
18:00
24:00
Time [h]
Figure 2: New particle formation event on 7 April, 2009.
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