Determination of free amino acids, saccharides, and selected microbes in biogenic atmospheric aerosols - seasonal variations, particle size distribution, chemical and microbial relations.

Primary biological aerosol particles (PBAPs) play an important role in the interaction between biosphere, atmosphere, and climate, affecting cloud and precipitation formation processes. The presence of pollen, plant fragments, spores, bacteria, algae, and viruses in PBAPs is well known. In order to explore the complex interrelationships between airborne and particulate chemical tracers (amino acids, saccharides), gene copy numbers (16S and 18S for bacteria and fungi, respectively), gas phase chemistry, and the particle size distribution, 84 size-segregated aerosol samples from four particle size fractions ( 10 mu m) were collected at the SMEAR II station, Finland, in autumn 2017. The gene copy numbers and size distributions of bacteria, Pseudomonas, and fungi in biogenic aerosols were determined by DNA extraction and amplification. In addition, free amino acids (19) and saccharides (8) were analysed in aerosol samples by hydrophilic interaction liquid chromatography-mass spectrometry (HILIC-MS). Different machine learning (ML) approaches, such as cluster analysis, discriminant analysis, neural network analysis, and multiple linear regression (MLR), were used for the clarification of several aspects related to the composition of biogenic aerosols. Clear variations in composition as a function of the particle size were observed. In most cases, the highest concentration values and gene copy numbers (in the case of microbes) were observed for 2.5-10 mu m particles, followed by > 10, 1-2.5, and < 1.0 mu m particles. In addition, different variables related to the air and soil temperature, the UV radiation, and the amount of water in the soil affected the composition of biogenic aerosols. In terms of interpreting the results, MLR provided the greatest improvement over classical statistical approaches such as Pearson correlation among the ML approaches considered. In all cases, the explained variance was over 91 %. The great variability of the samples hindered the clarification of common patterns when evaluating the relation between the presence of microbes and the chemical composition of biogenic aerosols. Finally, positive correlations were observed between gas-phase VOCs (such as acetone, toluene, methanol, and 2-methyl-3-buten-2-ol) and the gene copy numbers of microbes in biogenic aerosols.Peer reviewe

Measurement report : Atmospheric new particle formation in a coastal agricultural site explained with binPMF analysis of nitrate CI-APi-TOF spectra

The occurrence of new particle formation (NPF) events detected in a coastal agricultural site, at Qvidja, in Southwestern Finland, was investigated using the data measured with a nitrate ion-based chemicalionization atmospheric-pressure-interface time-of-flight (CI-APi-TOF) mass spectrometer. The binned positive matrix factorization method (binPMF) was applied to the measured spectra. It resulted in eight factors describing the time series of ambient gas and cluster composition at Qvidja during spring 2019. The most interesting factors related to the observed NPF events were the two factors with the highest mass-to-charge ratios, numbered 7 and 8, both having profiles with patterns of highly oxygenated organic molecules with one nitrogen atom. It was observed that factor 7 had elevated intensities during the NPF events. A variable with an even better connection to the observed NPF events is f(F7), which denotes the fraction of the total spectra within the studied mass-to-charge ratio range between 169 and 450Th being in a form of factor 7. Values of f(F7) higher than 0.50 +/- 0.05 were observed during the NPF events, of which durations also correlated with the duration of f(F7) exceeding this critical value. It was also observed that factor 8 acts like a precursor for factor 7 with solar radiation and that the formation of factor 8 is associated with ozone levels.Peer reviewe

Measurement report : The influence of traffic and new particle formation on the size distribution of 1–800 nm particles in Helsinki – a street canyon and an urban background station comparison

Peer reviewe

Confronting preconceptions on urban and agricultural environments: how local emissions influence atmospheric processes

Local emissions influence vapor and particle concentrations and therefore atmospheric processes and aerosol particle dynamics. Hence, local emissions can vary the chemical and physical properties of aerosol particles. This localized impact can be propagated to the regional scale affecting environmental challenges such as climate change and air pollution. In this thesis, the impact of local emissions on atmospheric concentrations was analyzed in urban and agricultural environments. At first, the influence of local emissions on particle and condensable vapor population was analyzed at a street canyon site and a nearby urban background station in Helsinki, Finland. The impact of traffic emissions was visible in sub-3 nm and nucleation mode particles at both stations to a different extent. Nevertheless, traffic emissions did not dominate the sub-3 nm particle concentration during daytime at the street canyon or the urban background stations. In the Aitken mode this influence was observed only in the street canyon. At both stations in Helsinki, the effect of anthropogenic emissions on highly oxygenated molecule (HOM) formation was observed to be similar: NOx impacted the oxidation of the volatile organic compounds. Nevertheless, there were only a few similarities in the chemical composition of organic condensable vapors between the street canyon and the urban background site. The spatial inhomogeneity of urban areas was observed in the composition of condensable vapors and particle size distributions and concentrations showing the importance of accounting for it while studying urban environments. Secondly, the influence of local emissions from agricultural grassland on precursor vapor and particle concentrations and therefore atmospheric processes was studied in Qvidja, Finland. The results show that new particle formation (NPF) over an agricultural field was driven by the clustering of sulfuric acid (SA) with locally emitted ammonia. Organic compounds can enhance this process and contribute to the growth of particles to the cloud condensation nuclei (CCN) relevant sizes. Additionally, the impact of local emissions was compared between the agricultural site and a forestry station (Hyytiälä, Finland). Both environments contributed to particle concentrations mainly by NPF and growth, but the NPF over agricultural field was more intense than in a forest. Hence, emissions from agricultural environment could have a stronger influence on climate than emissions from a forest. Overall, although rural areas are impacted similarly by local emissions, specifically via NPF and growth processes, the strength of that impact differs between locations. At the same time, urban areas within 1 km distance vary considerably due to the effect of local emissions. This variation imposes differences in atmospheric processes on the regional scale, hence it should not be overlooked.Paikalliset päästöt vaikuttavat höyry- ja pienhiukkaspitoisuuksiin ja sitä kautta ilmakehän prosesseihin ja pienhiukkasten dynamiikkaan. Näin ollen paikalliset päästöt voivat muokata pienhiukkasten kemiallisia ja fysikaalisia ominaisuuksia. Tämä paikallinen vaikutus voi laajeta myös alueellisen mittakaavan ilmiöihin, kuten ilmastonmuutokseen ja ilmanlaatuun. Tämän työn tarkoituksena on tutkia paikallisten päästöjen vaikutusta ilmakehän hiukkaspitoisuuksiin kahdessa erilaisessa ympäristössä Suomessa: kaupungissa (Helsinki) ja maatalousympäristössä (Qvidja). Työ kyseenalaistaa tyypilliset käsitykset näistä ympäristöistä: 1) vaikka kaupunkiympäristöjen tiedetään olevan heterogeenisiä, niitä käsitellään usein huomioiden vain ihmistoiminnasta aiheutuvat päästöt, ja 2) maatalouden päästöjä käsitellään monesti vain kasvihuonekaasujen osalta. Ihmistoiminnasta aiheutuvien päästöjen merkitys tiivistyvien höyryjen muodostumiseen Helsingissä havaittiin pääasiassa typen oksidien vaikutuksena kasvillisuuden päästämien haihtuvien hiiliyhdisteiden hapettumiseen. Tämä vaikutus havaittiin riippumattomaksi päästölähteiden intensiteetistä, käytännössä liikennemäärästä, mutta liikennemäärän havaittiin vaikuttavan sekä tiivistyvien höyryjen kemialliseen koostumukseen että pienten aerosolihiukkasten pitoisuuteen. Nämä suureet vaihtelivat merkittävästi pienilläkin etäisyyksillä, mikä osoittaa kaupunkialueiden alueellisen heterogeenisyyden merkityksen höyryjen ja pienhiukkasten ominaisuuksiin. Maatalousympäristössä Qvidjassa pellosta aiheutuvien paikallisten päästöjen vaikutus höyry- ja hiukkaspitoisuuksiin havaittiin pääasiassa uusien pienhiukkasten muodostumisessa. Tulosten mukaan pienhiukkasmuodostus heinäpellon yläpuolella aiheutui rikkihapon ja paikallisista päästöistä syntyneen ammoniakin klusteroitumisesta. Paikallisen kasvillisuuden päästämät hiiliyhdisteet voivat kiihdyttää tätä prosessia ja osallistua pienhiukkasten kasvuun pilvien muodostumiselle merkittäviin kokoihin asti. Vertailu maatalousympäristön ja metsäaseman (Hyytiälä) mittausdatojen välillä osoittaa, että molemmat ympäristöt vaikuttavat hiukkaspitoisuuksiin lähinnä pienhiukkasmuodostuksen ja hiukkasten kasvun kautta, mutta pienhiukkasmuodostumisen intensiteetti maatalousympäristössä on korkeampi kuin metsässä. Tämän perusteella edellä mainituilla maatalousympäristön päästöillä saattaa olla suurempi vaikutus ilmastoon kuin metsän päästöillä. Vaikka paikalliset päästöt metsistä ja maatalousalueilla vaikuttavat ilmakehän prosesseihin samojen mekanismien kautta, näiden vaikutusten vahvuus vaihtelee alueellisesti. Kaupunkiympäristöissä paikalliset päästöt aiheuttavat höyryjen ja pienhiukkasten ominaisuuksiin merkittävää vaihtelua alle kilometrin etäisyyksillä. Tätä vaihtelua ei tule jättää huomioimatta, sillä se vaikuttaa ilmakehän prosesseihin myös alueellisessa mittakaavassa

The synergistic role of sulfuric acid, ammonia and organics in particle formation over an agricultural land

Agriculture provides people with food, but poses environmental challenges. Via comprehensive observations on an agricultural land at Qvidja in Southern Finland, we were able to show that soil-emitted compounds (mainly ammonia and amines), together with available sulfuric acid, form new aerosol particles which then grow to climate-relevant sizes by the condensation of extremely low volatile organic compounds originating from a side production of photosynthesis (compounds emitted by ground and surrounding vegetation). We found that intensive local clustering events, with particle formation rates at 3 nm about 5-10 times higher than typical rates in boreal forest environments, occur on around 30% of all days. The requirements for these clustering events to occur were found to be clear sky, a low wind speed to accumulate the emissions from local agricultural land, particularly ammonia, the presence of low volatile organic compounds, and sufficient gaseous sulfuric acid. The local clustering will then contribute to regional new particle formation. Since the agricultural land is much more effective per surface area than the boreal forest in producing aerosol particles, these findings provide insight into the participation of agricultural lands in climatic cooling, counteracting the climatic warming effects of farming.Peer reviewe

Influence of anthropogenic emissions on the composition of highly oxygenated organic molecules in Helsinki : a street canyon and urban background station comparison

Peer reviewe