Tietokierto ilmakehäfysiikassa : mitatusta millivoltista ilmakehän ymmärtämiseen

In this thesis the concept of data cycle is introduced. The concept itself is general and only gets the real content when the field of application is defined. If applied in the field of atmospheric physics the data cycle includes measurements, data acquisition, processing, analysis and interpretation. The atmosphere is a complex system in which everything is in a constantly moving equilibrium. The scientific community agrees unanimously that it is human activity, which is accelerating the climate change. Nevertheless a complete understanding of the process is still lacking. The biggest uncertainty in our understanding is connected to the role of nano- to micro-scale atmospheric aerosol particles, which are emitted to the atmosphere directly or formed from precursor gases. The latter process has only been discovered recently in the long history of science and links nature s own processes to human activities. The incomplete understanding of atmospheric aerosol formation and the intricacy of the process has motivated scientists to develop novel ways to acquire data, new methods to explore already acquired data, and unprecedented ways to extract information from the examined complex systems - in other words to compete a full data cycle. Until recently it has been impossible to directly measure the chemical composition of precursor gases and clusters that participate in atmospheric particle formation. However, with the arrival of the so-called atmospheric pressure interface time-of-flight mass spectrometer we are now able to detect atmospheric ions that are taking part in particle formation. The amount of data generated from on-line analysis of atmospheric particle formation with this instrument is vast and requires efficient processing. For this purpose dedicated software was developed and tested in this thesis. When combining processed data from multiple instruments, the information content is increasing which requires special tools to extract useful information. Source apportionment and data mining techniques were explored as well as utilized to investigate the origin of atmospheric aerosol in urban environments (two case studies: Krakow and Helsinki) and to uncover indirect variables influencing the atmospheric formation of new particles.Tässä työssä esitellään konsepti - tietokierto ilmakehätieteissä. Tietokierto on sinänsä yleinen käsite ja ei liity mihinkään tiettyyn tieteenalaan. Tietokierto huomioi jokaisen vaiheen raa asta mittausarvosta datan soveltamiseen, ymmärtämiseen ja tulkintaan. Ilmakehäfysiikassa tietokierto sisältää vaiheet signaalin havainnoinnista, datan keräämiseen, esikäsittelyyn, ja työstämiseen sekä sitä kautta tulkintaan. Ilmakehä on monimutkainen kokonaisuus, jossa kaikki on jatkuvasti muuttuvassa tasapainossa keskenään. Tiedeyhteisö on yksimielisesti sitä mieltä, että kiihtyvä ilmastonmuutos on ihmisen toiminnan seurausta. Tarkalleen sitä prosessia ei kuitenkaan tunneta. Suurin epävarmuus ymmärryksessä on pienhiukkasten aiheuttama vaikutus ilmastomuutokseen. Pienhiukkasia päätyy ilmakehään joko suoraan päästölähteistä tai ne muodostuvat nukleaation eli kaasu-hiukkasmuuntuman kautta. Viimeksi mainittu ilmiö on havaittu vasta hiljattain ja sen yksityiskohtainen ymmärrys vielä puuttuu. Ilmiön monimutkaisuus on kiehtonut ja motivoinut tutkijoita kehittämään uusia mittalaitteistoja, mittausmenetelmiä, datan analysointimenetelmiä ja uusia tapoja suodattaa tietoa jo kerätystä datasta - toisin sanoen täydentää ja parantaa tietokiertoa. Aikaisemmin on ollut mahdotonta mitata suoraan kaasu-hiukkasmuuntumisessa osallistuvien kaasujen kemiallista koostumusta. Tässä työssä käytetty laitteisto (ilmakehäpaineliitännäinen lentoaikamassaspektrometri, APiTOF) pystyy havaitsemaan kyseisiä kaasuja suoraan ilman esikäsittelyä. Koska laitteisto on uusi ja sen tuottama data määrä on iso, kehitettiin tässä työssä tehokas raakadatan esikäsittelymenetelmä ja työkalu. Kun yhdistetään prosessoitu data useista laitteista, informaation sisältö kasvaa, mutta sen esille saaminen hankaloituu. Tässä työssä kehitettiin ja käytettiin menetelmiä ilmamassojen päästölähdekartoitukseen, tarkoituksena selvittää kaupunginympäristön pahimmat saastuttajat ja päästölähteet. Datan louhintaa hyödynnettiin löytämään kaasu-hiukkasmuuntumaan vaikuttavia tekijöitä

Cluster Measurements at CLOUD using a High Resolution Ion Mobility Spectrometer - Mass Spectrometer Combination

Mass spectrometry is powerful tool for environmental and atmospheric chemistry analysis. Modern mass spectrometers demonstrate low detection limits, high sensitivity, and high resolving power. However, such high performance is not always enough to identify ambient ion clusters due to the clusters braking at the atmospheric pressure-to-vacuum interface of mass spectrometer. This study presents a high resolution ion mobility spectrometer-time-of-flight mass spectrometer (IMS-TOF) in the CLOUD experiment. This combination of orthogonal analytical techniques allows obtaining structural information in addition to mass-to-charge separation

Molecular Steps of Neutral Sulfuric Acid and Dimethylamine Nucleation in CLOUD

We have run a set of experiments in the CLOUD chamber at CERN, Switzerland, studying the effect of dimethylamine (DMA) on sulfuric acid (SA)-water nucleation using a nitrate based Chemical Ionization Atmospheric Pressure ionization Time-Of-Flight Mass Spectrometer (CI-APi-TOF). Experiment was designed to produce neutral high m/z SA-DMA clusters in close to atmospherically relevant conditions to be detected and characterized by the CI-APi-TOF. We aimed in filling up the gap in measurement techniques from molecular level up to climatically relevant aerosol particles and thus improve our understanding of the role of sulfuric acid and DMA in atmospheric nucleation

Comprehensive analysis of particle growth rates from nucleation mode to cloud condensation nuclei in boreal forest

Growth of aerosol particles to sizes at which they can act as cloud condensation nuclei (CCN) is a crucial factor in estimating the current and future impacts of aerosol-cloud-climate interactions. Growth rates (GRs) are typically determined for particles with diameters (d(P)) smaller than 40 nm immediately after a regional new particle formation (NPF) event. These growth rates are often taken as representatives for the particle growth to CCN sizes (d(P) > 50-100 nm). In modelling frameworks, the concentration of the condensable vapours causing the growth is typically calculated with steady state assumptions, where the condensation sink (CS) is the only loss term for the vapours. Additionally, the growth to CCN sizes is represented with the condensation of extremely low-volatility vapours and gas-particle partitioning of semi-volatile vapours. Here, we use a novel automatic method to determine growth rates from below 10 nm to hundreds of nanometres from a 20-year-long particle size distribution (PSD) data set in boreal forest. With this method, we are able to detect growth rates also at times other than immediately after a NPF event. We show that the GR increases with an increasing oxidation rate of monoterpenes, which is closely coupled with the ambient temperature. Based on our analysis, the oxidation reactions of monoterpenes with ozone, hydroxyl radical and nitrate radical all are capable of producing vapours that contribute to the particle growth in the studied size ranges. We find that GR increases with particle diameter, resulting in up to 3-fold increases in GRs for particles with d(P) similar to 100 nm in comparison to those with d(P) similar to 10 nm. We use a single particle model to show that this increase in GR can be explained with aerosol-phase reactions, in which semi-volatile vapours form non-volatile dimers. Finally, our analysis reveals that the GR of particles with d(P) <100 nm is not limited by the condensation sink, even though the GR of larger particles is. Our findings suggest that in the boreal continental environment, the formation of CCN from NPF or sub-100 nm emissions is more effective than previously thought and that the formation of CCN is not as strongly self-limiting a process as the previous estimates have suggested.Peer reviewe

Chemistry of stabilized Criegee intermediates in the CLOUD chamber

In atmospheric conditions the oxidation of sulphur dioxide to sulphuric acid in gas phase has been considered to be determined by the concentration of hydroxyl radical. Recently the significance of stabilized Criegee intermediate as an oxidizer of sulphuric acid has been brought out. In this study we investigated the oxidation of sulphur dioxide in the CLOUD chamber in conditions where the hydroxyl radical was removed. The concentration of formed sulphuric acid was measured with a chemical ionization atmospheric pressure interface time-of-flight mass spectrometer and it was compared with the calculated yield of sulphuric acid

Characterization of positive clusters in the CLOUD nucleation experiments

The mechanism of new particle formation (NPF) events is still poorly understood. The CLOUD experiment is studying at which conditions this process occurs. During the CLOUD 7 campaign (fall 2012) the evolution of the nucleation rate with different reagents (sulphuric acid, ammonia, dimethylamine and α-pinene) was tested. Here we investigate the composition of freshly formed positive ions during the nucleation process, which allows us to understand the formation mechanisms of these clusters. The time evolution of the clusters is shown demonstrating the correlation between the formation of these clusters and the nucleation process

The Krakow Receptor Modelling Inter-Comparison Exercise

Second to oil, coal is globally the biggest energy source. Coal combustion is utilized mainly for power generation in industry, but in many metropolitan areas in East Europe and Asia also for residential heating in small stoves and boilers. The present investigation, carried out as a case study in a typical major city situated in a European coal combustion region (Krakow, Poland), aims at quantifying the impact on the urban air quality of residential heating by coal combustion in comparison with other potential pollution sources such as power plants, industry and traffic. For that purpose, gaseous emissions (NOx, SO2) were measured for 20 major sources, including small stoves and boilers, and the emissions of particulate matter (PM) was chemically analyzed for 52 individual compounds together with outdoor and indoor PM10 collected during typical winter pollution episodes. The data was analyzed using multivariate receptor modeling yielding source apportionments for PM10, B(a)P and other regulated air pollutants associated with PM10, namely Cd, Ni, As, and Pb. The source apportionment was accomplished using the chemical mass balance modeling (CMB) and constrained positive matrix factorization (CMF) and compared to five other multivariate receptor models (PMF, PCA-MLRA, UNMIX, SOM, CA). The results are potentially very useful for planning abatement strategies in all areas of the world, where coal combustion in small appliances is significant. During the pollution episodes under investigation the PM10 and B(a)P concentrations were up to 8-200times higher than the European limit values. The major culprit for these extreme pollution levels was shown to be residential heating by coal combustion in small stoves and boilers (>50% for PM10 and >90% B(a)P), whereas road transport (<10% for PM10 and <3% for B(a)P), and industry (4-15% for PM10 and <6% for B(a)P) played a lesser role. The indoor PM10 and B(a)P concentrations were not much lower than the outdoor concentrations and were found to have the same sources as outdoor PM10 and B(a)P The inorganic secondary aerosol component of PM10 amounted to around 30%, which may be attributed for a large part to the industrial emission of the precursors SO2 and NOX.JRC.H.4-Transport and air qualit

Nucleation of H_2SO_4 and oxidized organics in CLOUD experiment

The research of atmospheric new particle formation has proceeded lately as the role of sulphuric acid has been established. Still, the roles of other atmospheric compounds in nucleation remain largely unclear. To clarify the first steps of atmospheric new particle formation extensive nucleation experiments were performed in CLOUD chamber in 2012. Especially the role of oxidations products of α-pinene was studied in detail. The experiments provided new information about the part of oxidized organics in nucleation

Applicability of condensation particle counters to measure atmospheric clusters

This study presents an evaluation of a pulse height condensation particle counter (PH-CPC) and an expansion condensation particle counter (E-CPC) in terms of measuring ambient and laboratory-generated molecular and ion clusters. Ambient molecular cluster concentrations were measured with both instruments as they were deployed in conjunction with an ion spectrometer and other aerosol instruments in Hyytiälä, Finland at the SMEAR II station between 1 March and 30 June 2007. The observed cluster concentrations varied and ranged from some thousands to 100 000 cm -3. Both instruments showed similar (within a factor of ~5) concentrations. An average size of the detected clusters was approximately 1.8 nm. As the atmospheric measurement of sub 2-nm particles and molecular clusters is a challenging task, we conclude that most likely we were unable to detect the smallest clusters. Nevertheless, the reported concentrations are the best estimates to date for minimum cluster concentrations in a boreal forest environment