Overview of the field measurement campaign in Hyytiälä, August 2001 in the framework of the EU project OSOA
[摘要] As part of the OSOA (Origin and formation of Secondary Organic Aerosols)project, two intensive field campaigns were conducted in Melpitz, Germanyand Hyytiälä, Finland. This paper gives an overview of themeasurements made during the Hyytiälä campaign, which was heldbetween 1 and 16 August 2001. Various instrumentaltechniques were used to achieve physical and chemical characterisation ofaerosols and to investigate possible precursor gases.
During the OSOA campaign in Hyytiälä, particle formation wasobserved on three consecutive days at the beginning of the campaign(1 to 3 August 2001) and on three days later on. Theinvestigation of the meteorological situation divided the campaign into twoparts. During the first three days of August, relatively cold and clean airmasses from northwest passed over the station (condensation sink – CS: <0.002 s-1,NOx: <0.5 ppb). Daily particle bursts of onefraction of the nucleation mode aerosols (3–10 nm) with numberconcentrations between 600–1200 particles cm-3 were observed. Afterthis period, warmer and more polluted air from south-west to south-eastarrived at the station (CS: 0.002–0.01 s-1, NOx: 0.5–4 ppb)and during these 13 days only three events were observed. These events werenot as apparent as those that occurred during the earlier period of thecampaign. The chemical analyses from different institutes of PM2,PM2.5 and PM10 particles confirmed the assumption that organicmatter from the oxidation of various terpenes contributed to the formationof secondary organic aerosols (SOA). Concerning these conclusions amongothers, the ratio between formic (oxidation product of isoprene andmonoterpenes by ozone) and acetic acid (increased by anthropogenicemissions) (ratio=1 to 1.5) and concentration of different carboxylicacids (up to 62 ngm-3) were investigated. Gas/particle partitioning offive photo-oxidation products from α- and β-pinene resultedin higher concentrations of pinonic, nor pinonic and pinic acids in theparticle phase than in the gas phase, which indicates a preference to theparticle phase for these compounds. The average growth factors (GF) from 100 nmparticles in water vapour gave a diurnal pattern with a maximum duringdaytime and values between 1.2 and 1.7. On average, the amount of secondaryorganic carbon reached values around 19% of the sampled aerosols andwe speculate that formation of SOA with the influence of photo-oxidationproducts from terpenes was the reason for the observed particle burstsduring the campaign. However, correlations between the precursor gases orthe favourable condensing species with the monitored nucleation modeparticles were not found. For the investigated time period other factorslike the condensation sink of newly formed particles to the pre-existingaerosols, temperature and solar irradiance seem to be more importantsteering parameters for the production of new aerosols.Another open question concerns the vertical distribution of the formation ofSOA. For this reason measurements were conducted at different altitudesusing a tethered balloon platform with particle sampling and particlecounting equipment. They were incorporated with eddy covariance (EC) fluxmeasurements made at 23 m above ground level. The results give firstindications that production of new aerosols happens throughout the planetaryboundary layer (PBL), whereby different parameters e.g. temperature, CS,solar irradiance or concentration of monoterpenes are responsible for thelocation of the vertical maximum.
