Browsing by study line "Aerosolifysiikka"

Urban areas account for 70% of worldwide energy-related CO2 emissions and play a significant role in the global carbon budget. With the enhanced consumption of fossil fuel and the dramatic change in land use related to urbanization, control and mitigation of CO2 emissions in the urban area is becoming a major concern for urban dwellers and city managers. It is of great importance and demand to estimate the local CO2 emissions in urban areas to assess the effectiveness of mitigation regulation. Surface Urban Energy and Water Balance Scheme (SUEWS) incorporated with a CO2 exchange module provides an advanced method to model total urban CO2 flux and quantify the different local-scale emission sectors involving transportation, human metabolism, buildings and vegetation. Using appropriate input data such as detailed site information and meteorological condition, it can simulate the local or neighbourhood scale CO2 emissions in a specific period, or even under a future scenario. In this study, the SUEWS model is implemented in an urban region, Jätkäsaari, which is an extension of Helsinki city centre, to simulate anthropogenic and biogenic CO2 emissions in the past and future. The construction of this district started in 2009 and was planned to be completed in 2030. Therefore, this region is a good case to investigate the impacts of urban planning on urban CO2 emissions. Based on the urban surface information, meteorological data, and abundant emission parameters, a simulation in this 1650 × 1400 m area with the spatial resolution of 50 × 50 m and the time resolution of an hour was conducted with the aim to get information on the total annual CO2 emissions, and the temporal and spatial variability of CO2 fluxes from different sources and sink in 2008 and 2030. The positive CO2 fluxes indicate the CO2 sources, while the negative indicate the CO2 sinks. In both of the previous and future case, the spatial variation of net CO2 fluxes in Jätkäsaari is dominated by the distribution of traffic and human activities. From April to September, the vegetation acts as the CO2 sink with negative net ecosystem exchange. In 2008, the modelled cumulative CO2 flux is 3.0 kt CO2 year-1, consisting of 1.9 kt CO2 year-1 from metabolism, 1.9 kt CO2 year-1 from traffic, 0.5 kt CO2 year-1 from soil and vegetation respiration, as well as -1.3 kt CO2 year-1 from photosynthesis. In 2030, the total annual CO2 emissions increase to 11.1 kt CO2 year-1 because of the rising traffic volume and amount of inhabitants. Road traffic became the dominant CO2 sources, accounting for 53% of the total emissions. For the diurnal variation, in 2008, the study area remains the CO2 sources with the exception of summertime morning when the net CO2 flux is negative, while in 2030, the net CO2 flux is positive in the whole day.

Atmospheric aerosol particles play a significant role in urban air pollution, and understanding their size distribution is essential for assessing pollution sources and urban aerosol dynamics. In this study, we use a novel method developed by Kontkanen et al. (2020) to determine size-resolved particle number emissions in the particle size range of 3-800 nm at an urban background site and a street canyon site in Helsinki. Our results show overall higher particle number emissions in the street canyon compared to the urban background. On non-NPF event days, the particle number emissions of 3-6 nm particles in the urban background are highest in the noon. The emissions to the size range of 6-30 nm are highest during the morning or afternoon at both sites, indicating traffic is the main particle source in this size range. The emissions of larger particles are relatively low. Seasonal analysis suggests higher emissions during the summer in comparison to the winter which might be linked to higher product of mixing layer height (MLH) and particle number concentration in summer. Further investigations into particle emissions from different wind sectors suggest higher particle emissions from the urban sector than from the road sector in the urban background, contrary to the results for NOx concentrations. More research is needed to better understand the underlying factors. In addition, a comparison between particle number emissions estimated using FMI measurement MLH data and ERA5 model MLH data reveals that FMI data provides a more reliable representation of the MLH in the study area. Overall, the methods show limitations in accurately capturing particle dynamics in Helsinki. Future studies should address these limitations by employing more accurate NPF event classification and refining sector division methods.

We investigated the impact of various parameters on new particle formation rates predicted for the sulfuric acid - ammonia system using cluster distribution dynamics simulations, in our case ACDC (Atmospheric Cluster Dynamics Code). The predicted particle formation rates increase significantly if rotational symmetry number of monomers (sulfuric acid and ammonia molecules, and bisulfate and ammonium ions) are considered in the simulation. On the other hand, inclusion of the rotational symmetry number of the clusters only changes the results slightly, and only in conditions where charged clusters dominate the particle formation rate because most of the clusters stable enough to participate in new particle formation display no symmetry, therefore have a rotational symmetry number of one, and the few exceptions to this rule are positively charged. Further, we tested the influence of the application of a quasi-harmonic correction for low-frequency vibrational modes. Generally, this decreases predicted new particle formation rates, and significantly alters the shape of the formation rate curve plotted against the sulfuric acid concentration. We found that the impact of the maximum size of the clusters explicitly included in the simulations depends on the simulated conditions and the errors due to the limited set of clusters simulated generally increase with temperature, and decrease with vapor concentrations. The boundary conditions for clusters that are counted as formed particles (outgrowing clusters) have only a small influence on the results, provided that the definition is chemically reasonable and the set of simulated clusters is sufficiently large. We compared predicted particle formation rates with experimental data measured at the CLOUD (Cosmics Leaving OUtdoor Droplets) chamber. A cluster distribution dynamics model shows improved agreement with experiments when using our new input data and the proposed combination of symmetry and quasi-harmonic corrections., compared to an earlier study based on older quantum chemical data.

This thesis investigates the impact of the energy crisis on air quality in the Po Valley, Italy, with a focus on the effect of changes in methane consumption over the potential changes in wood burning consumption. The study employs the WRF-CHIMERE model to simulate the consequences of varying wood burning consumption on air quality. Observational data of benzo[a]pyrene and PM2.5 concentrations in the Po Valley are also analyzed. The results indicate that meteorological conditions have a significant influence on air quality, overshadowing the potential effects of emission changes resulting from the energy crisis. However, we observed a model’s bias correlated to the planetary boundary layer height, which could have influenced this result. Further investigation is necessary to correct this bias and comprehensively understand the relationship between energy consumption, air quality, and meteorology in the Po Valley.

After 2013, the environmental protection department in China has significantly reduced on-road emission through the upgrade of emission standards, the improvement of fuel quality and economic tools. However, the specific effect of the control policies on emission and air quality is still difficult to quantify. This is mainly due to the data shortage on vehicle emission factors and vehicle activities. In this research, we developed the 2008-2018 on-road emissions inventory based on Emission Inventory Preparation Guide (GEI) and existing vehicle activity database. Our estimates suggest that CO and PM2.5 showed a relatively significant decrease, by 66.2% and 58.8%. However, the trend of NOx (5.8%) and NMVOC (-4.8%) was relatively stable. The Beijing-Tianjin-Hebei (BTH), Yangtze River Delta (YRD), Pearl River Delta (PRD) and Sichuan Basin (SCB) regions all showed a uniform trend especially in NOx. For Beijing-Tianjin-Hebei, the significant decline in NOx might be caused by earlier implementations in emission standard and fuel quality. In addition to this, we designed additional evaporation emission scenarios to verify the application of GEI in quantify emission impact on secondary pollutant (PM2.5 and O3). The results indicate that evaporation emission contributed to Maximum Daily Average 8-hour (MDA8) O3 concentration by about 3.5%, for Beijing, Shanghai and Nanjing. This value can reach up to 5.9%, 5.3% and 7.3%, but the impact on PM2.5is extremely limited. Our results indicate the feasibility of GEI in improving and lowering the technical barrier of on-road emission inventory establishment at the same time and its further application in quantifying on-road emission contribution to air quality. Besides that, it shows a strong potential in on-road policy environmental assessment and short-term air quality assessment.

The impacts of dust aerosols on human health and climate change are increasing as the particulate matter (PM) mass concentrations and frequency of Sand and Dust Storm (SDS) episodes have shown an increasing trend in recent studies, especially for the Middle East and North Africa (MENA). In this thesis, particulate matter (PM10 and PM2.5) concentrations were measured during May 2018–March 2019 in the urban atmosphere of Amman, Jordan. The PM sampling was 24-hours every 6 days. The overall mean PM10 mass concentration was 64±39 μg/m3 with the median (+interquartile range) value of 49.2+53.5 μg/m3, the PM2.5 mass concentration varied between 15 μg/m3 and 190 μg/m3 with an annual average 47±32 μg/m3 and with the median (+interquartile range) value of 35.8+26.3 μg/m3. The PM2.5 / PM10 ratio was 0.8±0.2. According to the Jordanian Air Quality standards, the annual mean PM10 needs to be below a limit value of 120 μg/m3, which was true in this work. However, the PM2.5 mass concentration was three times higher the corresponding limit value (65 μg/m3). However, both exceeded the World Health Organization (WHO) air quality annual guideline of 20 μg/m3 for PM10 and 10 μg/m3 for PM2.5. The results show that the observed PM10 mass concentrations in Jordan were lower than what was reported in other cities in the Middle East but were higher when compared to other Mediterranean cities. During the measurement period, Jordan was affected by Sand and Dust Storms (SDS), which were observed on 14 sampling days. The source origins of these SDS were traced back to North Africa, the Arabian Peninsula, and the Levant. The 24-hour PM10 concentrations during these SDS episodes ranged between 108.1 μg/m3 and 187.3 μg/m3. In the future, measurements with a higher time resolution (one sample per day) are recommended for a more precise seasonal trend interpretation.

Cloud condensation nuclei (CCN) participate in controlling the climate, and a better understading of their number concentrations is needed to constrain the current uncertainties in Earth’s energy budget. However, estimating the global CCN concentrations is difficult using only localised in-situ measurements. To overcome this, different proxies and parametrisations for CCN have been developed. In this thesis, accumulation mode particles were used as a substitute for CCN, and continental proxy for number concentration of N100 was developed with CO and temperature as tracers for anthropogenic and biogenic emissions. The data utilised in the analysis contained N100 measurements from 22 sites from 5 different continents as well as CO and temperature from CAMS reanalysis dataset. The thesis aimed to construct a global continental proxy. In addition to this, individual proxies for each site (the site proxy) and proxies trained with other sites’ data (the site excluded proxy) were developed. The performance of these proxies was evaluated using a modified version of K-fold cross-validation, which allowed estimating the effect of dataset selection on the results. Additionally, time series, seasonal variation, and parameter distributions for developed proxies were analysed and findings compared against known characteristics of the sites. Global proxy was developed, but no single set of parameters, that would achieve the best performance at all sites, was found. Therefore, two versions of global proxy were selected and their results analysed. For most of the sites, the site proxy performed better than the global proxies. Additionally, based on the analysis from the site excluded proxy, extrapolating the global proxy to new locations produced results with varying accuracy. Best results came from sites with low concentrations and occasional anthropogenic transport episodes. Additionally, some European rural sites performed well, whereas in mountainous sites the proxy struggled. Comparing the proxy to literature, it performed generally less well or similarly as proxies from other studies. Longer datasets and additional measurement sites could improve the proxy performance.

Atmospheric aerosol particles affect Earth’s radiation balance, human health and visibility. Secondary organic aerosol (SOA) contributes a significant fraction to the total atmospheric organic aerosol, and thus plays an important role in climate change. SOA is formed through oxidation of volatile organic compounds (VOCs) and it consists of many individual organic compounds with varying properties. The oxidation products of VOCs include highly oxygenated organic molecules (HOM) that are estimated to explain a large fraction of SOA formation. To estimate the climate impacts of SOA it is essential to understand its properties in the atmosphere. In this thesis, a method to investigate thermally induced evaporation of organic aerosol was developed. SOA particles were generated in a flow tube from alpha-pinene ozonolysis and then directed into a heated tube to initiate particle evaporation. The size distribution of the particles was measured with parallel identification of the evaporated HOM. This method was capable of providing information of SOA evaporation behaviour and the particle-phase composition at different temperatures. Mass spectra of the evaporated HOM and particle size distribution data were analyzed. The obtained results suggest that SOA contains compounds with a wide range of volatilities, including HOM monomers, dimers and trimers. The volatility behaviour of the particulate HOM and their contribution to SOA particle mass was studied. Furthermore, indications of particle-phase reactions occurring in SOA were found.