Anne Hirsikko

A simple procedure for correcting loading effects of aethalometer data

A simple method for correcting for the loading effects of aethalometer data is presented. The formula BC(CORRECTED) = (1 + k x ATN) x BC(NONCORRECTED), where ATN is the attenuation and BC is black carbon, was used for correcting aethalometer data obtained from measurements at three different sites: a subway station in Helsinki, an urban background measurement station in Helsinki, and a rural station in Hyytiälä in central Finland. The BC data were compared with simultaneously measured aerosol volume concentrations (V). After the correction algorithm, the BC-to-V ratio remained relatively stable between consequent filter spots, which can be regarded as indirect evidence that the correction algorithm works. The k value calculated from the outdoor sites had a clear seasonal cycle that could be explained by darker aerosol in winter than in summer. When the contribution of BC to the total aerosol volume was high, the k factor was high and vice versa. In winter, the k values at all wavelengths were very close to that obtained from the subway station data. In summer, the k value was wavelength dependent and often negative. When the k value is negative, the noncorrected BC concentrations overestimated the true concentrations.

Aerosol size distribution measurements at four Nordic field stations : identification, analysis and trajectory analysis of new particle formation bursts

We analyzed aerosol size distributions from the Finnish measuring stations at Hyytiälä, Värriö and Pallas and the Swedish station at Aspvreten over a period of several years.We identified occurrences of new particle formation bursts and obtained characteristics for the bursts from the size distribution data. In addition, we analyzed the directions from which air masses leading to new particle formation arrived.We found that new particle formation occurs over the whole area covered by the measurement stations. The Northern Atlantic is dominating as a source for air leading to new particle formation at all of the analyzed stations. The formation occurrence had a similar annual variation at all the stations, with peaks in springtime and autumn and minima in winter and summer. The ratio of event days to non-event days had a North-South dependence, with northern stations having lower event ratios. Particle growth rates ranged from 0.5 to 15 nm/h, with the mean growth rate being slightly higher at the southern stations. Southern stations also had a stronger particle source, on average 0.5 cm-3 s-1, compared to the northern stations (0.1 cm-3 s-1). Based on our analysis, it is evident that new particle formation occurs often in whole Nordic boreal forest area when air is transported from the North Atlantic, and that the same process or processes are very probably responsible for the formation over the whole area.

Aerosol particle formation events and analysis of high growth rates observed above a subarctic wetland-forest mosaic

An analysis of particle formation (PF) events over a subarctic mire in northern Swedenwas performed, based on number– size distributions of atmospheric aerosol particles (10–500 nm in diameter) and ions (0.4–40 nm in Tammet diameter). We present classification statistics for PF events from measurements covering the period July 2005–September 2006, with a break over the winter period. The PF event frequency peaked during the summer months, in contrast to other Scandinavian sites where the frequency is highest during spring and autumn. Our analysis includes calculated growth rates and estimates of concentrations and production rates of condensing vapour, deduced from the growth rates and condensational sink calculations, using AIS and SMPS data. Particle formation events with high growth rates (up to 50 nm h-1) occurred repeatedly. In these cases, the newly formed nucleation mode particles were often only present for periods of a few hours. On several occasions, repeated particle formation events were observed within 1 d, with differences in onset time of a few hours. These high growth rates were only observed when the condensation sink was higher than 0.001 s-1.

Observations on nocturnal growth of atmospheric clusters

In this paper, we summarize recent observations of nighttime nucleation events observed during 4 yr, from 2003 to 2006, at the SMEAR II station in Hyytiäläa, southern Finland. Formation of new atmospheric aerosol particles has been frequently observed all around the world in daytime, but similar observations in nighttime are rare. The recently developed ion spectrometers enabled us to measure charged aerosol particles and ion clusters to diameters < 1 nm and are efficient tools for evaluating cluster dynamics during nighttime. We observed clear growth of cluster ions during approximately 60 nights per yr. The newly formed intermediate ions usually persisted for several hours with typical concentrations of 100–200 cm-3. The evolution of nighttime growth events is different compared with daytime events. The mechanism behind nighttime events is still unclear, but the behaviour can be described by the hypothesis of activation of clusters.

JOYCE: Jülich Observatory for Cloud Evolution

AbstractThe Julich Observatory for Cloud Evolution (JOYCE), located at Forschungszentrum Julich in the most western part of Germany, is a recently established platform for cloud research. The main objective of JOYCE is to provide observations, which improve our understanding of the cloudy boundary layer in a midlatitude environment. Continuous and temporally highly resolved measurements that are specifically suited to characterize the diurnal cycle of water vapor, stability, and turbulence in the lower troposphere are performed with a special focus on atmosphere–surface interaction. In addition, instruments are set up to measure the micro- and macrophysical properties of clouds in detail and how they interact with different boundary layer processes and the large-scale synoptic situation. For this, JOYCE is equipped with an array of state-of-the-art active and passive remote sensing and in situ instruments, which are briefly described in this scientific overview. As an example, a 24-h time series of the ev...

Hot-air Balloon Measurements of Vertical Variation of Boundary Layer New Particle Formation

In this study, we used a hot-air balloon as a platform for boundary layer particle and cluster measurements. We did altogether 11 flights during the spring of 2005 and 2006. During the spring of 2006, we observed five new particle formation days. During all days, new particle formation took place in the mixed boundary layer. During one of the days, we observed particle formation in the free troposphere, separate from that of the mixed layer. The observations showed that the concentration of freshly-formed 1.5-2 nm negative ions was several times higher than the concentration of positive ions. We also clearly observed that nucleation during one of the days, 13 March 2006, was a combination of neutral and ion-induced nucleation. During some of the days, particle growth stopped at around 3 nm, probably due to lack of condensable organic vapours. Simulations of boundary layer dynamics showed that particles are formed either throughout the mixed layer or in the lower part of it, not at the top of the layer.

Air Ion Measurements During a Cruise from Europe to Antarctica

Latitudinal air ion mobility distribution variations were characterized in the marine boundary layer during a cruise over the Eastern Atlantic and Southern Ocean. We measured concentrations of cluster ions and charged aerosol particles in the size range of 0.4–40 nm. The measured ion mobility distributions were characterized and classified according to meteorological conditions and air mass back-trajectories. New particle formation episodes (bursts of intermediate air ions) were observed above the pack-ice region of the Southern Ocean and several times during showers in the tropical marine boundary layer.

Aerosol optical properties in Finland during Russian forest fires in 2010

Effects of the pollution plume originating from the Russian forest fires in summer 2010 on the aerosol properties in Finland were analyzed. Main properties were AOD and AE measured with Cimel and PFR sun photometers at five stations. In addition, scattering and absorption coefficient, aerosol particle number concentration and meteorological parameters were measured on the surface air. AATSR and MODIS AOD data were used to get a picture about the regional distribution of the plume. Two clear extreme periods of the AOD were observed. On 30th July, the maximum AOD was detected in Sodankyla, being 0.9 at 550 nm. A more impressive episode was between the 6th and 8th of August, when the extreme AOD of 1.5 was measured in Kuopio. In-situ observations suggest that the major part of the aerosol was residing in the well mixed layer coupled with the surface.

Ground-based remote sensing profiling of aerosols and mass concentration above Mace Head, Ireland

Two techniques based on synergistic in-situ and ground-based remote sensing instrumentation to retrieve the vertical structure of the atmospheric boundary layer (ABL) and the aerosol mass concentration from the LIDAR extinction are presented. The vertical structure of the ABL during day and night is retrieved by applying the Temporal Height Tracking algorithm to the backscatter and Doppler velocity LIDAR profiles; the calculation of the extinction coefficient from LIDAR returns in combination with in-situ aerosol measurements allow the characterization and categorization of different aerosol layers as well as the estimate of the aerosol mass concentration profile.