Veijo Hiltunen

Diurnal and annual characteristics of particle mass and number concentrations in urban, rural and Arctic environments in Finland

Abstract In order to be able to detect annual and diurnal variation the nucleation, Aitken and accumulation mode aerosol number concentrations were investigated. In this study particulate matter and aerosol number concentrations based on three years (1999–2001) measurements in four different places, Helsinki, Hyytiala, Pallas and Varrio in Finland were utilized. Mean PM10 concentration was found to be in urban, urban background, disturbed rural and rural conditions 18.7, 15.3, 10.2 and 6.9 μg m −3 . PM2.5 concentrations in urban, urban background and rural conditions were 9.6, 8.2 and 5.8 μg m −3 . PM1 concentration in rural area were 4.1 μg m −3 . Total number concentrations between 10 and 500 nm in urban, rural and arctic background were 16660, 2110 and about 920 cm −3 , respectively. Annual cycle of different particle sizes was also investigated. Particle mass was found to have maximum during the spring and autumn. Nucleation mode particle concentrations had their maximum both in urban and rural conditions in spring and autumn. For Aitken mode a similar variation was found. Accumulation mode particles were found to have the highest concentrations during summer and the lowest concentrations during winter. In urban conditions local sources drive over natural variability, but a natural cycle can still be seen. Diurnal variation was found to be associated with traffic in urban conditions. In rural conditions, diurnal variation of nucleation mode particles were connected to new particle formation. It was also found, that there is no correlation between ultrafine ( nm ) and larger (>90 nm ) particles.

Chemical composition of aerosol during particle formation events in boreal forest

Size-segregated chemical aerosol analysis of a total 5 integrated samples has been performed for the atmospheric aerosol during events of new particle formation. The experiments were conducted during the BIOFOR 3 measurement campaign at a boreal forest site in southern Finland in spring 1999. Aerosol samples collected by a cascade low-pressure impactor were taken selectively to distinguish particle formation event aerosol from non-event aerosol. The division into “event” and “non-event” cases was done “in situ” at field, based on the on-line submicron number size distribution. The results on the chemical ionic composition of the particles show only small differences between the event and non-event sample sets. The event samples show lower concentrations of total sulfate and ammonium as well as light dicarboxylic acids such as oxalate, malonate and succinate. In the event samples, nucleation mode particle MSA (methanesulphonic acid) was found to be present exceeding the concentrations found in the non-event samples, but at larger particle sizes the sample sets contained rather similar concentrations of MSA. The most significant difference between the event and non-event sets was found for dimethylammonium, ionic component of dimethylamine ((CH3)2NH), which seems to be present in the particle phase during the particle formation periods and/or during the subsequent particle growth. The absolute event sample dimethylamine concentrations were more than 30-fold greater than the non-event concentrations in the accumulation mode size range. On the other hand, the non-event back-up filter stage for sub-30 nm particles contained more dimethylamine than the event samples. This fractionation is probably a condensation artifact of the impactor sampling. A simple mass balance estimate is performed to evaluate the quality and consistency of the results for the overall mass concentration.

Measurements of aerosol particle dry deposition velocity using the relaxed eddy accumulation technique

The continuous measurements of aerosol particle deposition velocity have been performed from January 2004 to January 2005 using a REA technique with dynamic deadband.We measured aerosol particle deposition velocity in the size range of 10–150 nanometer with 5–10 nanometer steps using differential mobility analyser for sizing.We were able to measure two size classes simultaneously. One size class was changed at one month intervals, another we kept constant at 30 nm to investigate the effect of seasonal and meteorological variation on deposition velocity. We found that the 80–100 nanometer size particles had the lowest deposition velocity, about 0.4 cm s−-1. Deposition velocity increased with decreasing or increasing particle diameter from 80–100 nanometer size. We also found that deposition velocity increases as a function of friction velocity.

Aromatic hydrocarbon and methyl tert-butyl ether measurements in ambient air of Helsinki (Finland) using diffusive samplers.

The diffusive sampling method was evaluated for measuring benzene, toluene, ethylbenzene, xylenes, styrene, propylbenzene, ethyltoluenes, trimethylbenzenes and methyl tert-butyl ether (MTBE) in the urban air of Helsinki, Finland. Concentrations were measured in 2-week periods at four different sites during the year 2000. Tube type adsorbent tubes were pre-packed with Carbopack-B (60/80). Analysis was conducted using thermal desorption and gas chromatograph coupled to a mass spectrometer. In different seasons, during five diffusive sampling periods, parallel measurements were conducted using pumped and online sampling. The compared techniques agreed reasonably well for other compounds than trimethylbenzenes. Based on comparisons, diffusive uptake rates for ethyltoluenes, styrene, propylbenzene and MTBE were determined, and for trimethylbenzenes, uptake rates were revised. The concentrations of aromatic compounds in Helsinki metropolitan area were also compared to the concentrations of a rural, forested site in Central Finland.