Ville Vakkari

Reevaluating the contribution of sulfuric acid and the origin of organic compounds in atmospheric nanoparticle growth

Aerosol particles formed in the atmosphere are important to the Earths climate system due to their ability to affect cloud properties. At present, little is known about the atmospheric chemistry responsible for the growth of newly formed aerosol particles to climate-relevant sizes. Here combining detailed aerosol measurements with a theoretical framework we found that depending on the gaseous precursors and size of the newly formed particles, the growth was dominated by either sulfuric acid accompanied by ammonium or organic compounds originating in either biogenic emissions or savannah fires. The contribution of sulfuric acid was larger during the early phases of the growth, but in clean conditions organic compounds dominated the growth from 1.5 nm up to climatically relevant sizes. Furthermore, our analysis indicates that in polluted environments the contribution of sulfuric acid to the growth may have been underestimated by up to a factor of 10.

Submicrometer aerosols and excess CO as tracers for biomass burning air mass transport over southern Africa

This paper links surface measurements of biomass burning aerosols and trace gases with trajectory analysis to determine transport pathways for air masses with high and low concentrations. We interpret the long-term atmospheric monitoring record from a remote monitoring station in central southern Africa (North West Province, South Africa). Trace gas analyzers and a Differential Mobility Particle Sizer were used to measure ground level trace gas and submicron aerosol concentrations. Fire signatures were identified based on excess CO above average tropospheric levels, and episodes of enhanced particulate matter concentrations in the 10 to 840 nm size range. Thirty-six biomass burning plumes were reported; 7 had strong signals of excess CO, with ratios between 0.41 and 0.64, while 29 had weak signals ranging between 0.07 and 0.32. Pathways identified for the long-range transport of biomass burning aerosols were as follows: easterly (39% frequency), southwesterly (31%), recirculation (22%), and northerly (8%) flow patterns. CO and Aitken-mode aerosol number strengths were larger for fire emissions arriving in the easterly and southwesterly air masses than for recirculation and northerly air masses. Easterly and southwesterly flows were dominated by Aitken-mode aerosol, whereas accumulation-mode particles dominated in the recirculation and northerly flows. Findings identify biomass burning as a major source of Aitken-mode aerosols. Enhanced CO concentrations, combined with Aitken- and accumulation-mode particle number size distributions, are shown to provide a useful signature of plumes originating over regional biomass combustion events.

Low-Level Jets over Utö, Finland, Based on Doppler Lidar Observations

AbstractOver two years of meteorological observations from Uto, a small island in the Finnish outer archipelago in the Baltic Sea, were used to investigate the occurrence and characteristics of low-level jets (LLJs) and the diurnal and seasonal variations in these properties. An objective LLJ identification algorithm that is suitable for high-temporal-and-vertical-resolution Doppler lidar data was created and applied to wind profiles obtained from a combination of Doppler lidar data and two-dimensional sonic anemometer observations. This algorithm was designed to identify coherent LLJ structures and requires that they persist for at least 1 h. The long-term mean LLJ frequency of occurrence at Uto was 12%, the mean LLJ wind speed was 11.6 m s−1, and the vast majority of identified LLJs occurred below 150 m above ground level. The LLJ frequency of occurrence was much higher during summer (21%) and spring (18%) than in autumn (8%) and winter (3%). During winter and spring, the LLJ frequency of occurrence is ...

Estimating the concentration of nucleation mode aerosol particles over South Africa using satellite remote sensing measurements

In this work satellite based observations were used to estimate the concentration of nucleation mode aerosols over South Africa. The nucleation mode aerosols can not be detected directly with satellite instruments since they are much smaller than the optically active aerosols, hence the concentrations were estimated using proxies introduced by Kulmala et al. (2011). Results showed enhanced values of both primary and regional scale nucleation proxies over the Mpumalanga Highveld industrial area, whereas over the Johannesburg-Pretoria megacity only the primary nucleation proxy showed elevated values. To estimate how well satellite based proxies work, the relation between satellite and in situ based quantities was studied in more detail. The correlation between aerosol optical depth (AOD) and condensation sink (CS) was 0.2-0.3 depending on the location. Boundary layer height affected the correlation somewhat, but there are other factors, such as the effect of dust on AOD, that are more likely to have a stron...

Major secondary aerosol formation in southern African open biomass burning plumes

Open biomass burning contributes significantly to air quality degradation and associated human health impacts over large areas. It is one of the largest sources of reactive trace gases and fine particles to Earth’s atmosphere and consequently a major source of cloud condensation nuclei on a global scale. However, there is a large uncertainty in the climate effect of open biomass burning aerosols due to the complexity of their constituents. Here, we present an exceptionally large dataset on southern African savannah and grassland fire plumes and their atmospheric evolution, based on 5.5 years of continuous measurements from 2010 to 2015. We find that the mass of submicrometre aerosols more than doubles on average, in only three hours of daytime ageing. We also evaluate biomass burning aerosol particle size distributions and find a large discrepancy between the observations and current model parameterizations, especially in the 30–100 nm range. We conclude that accounting for near-source secondary organic aerosol formation and using measurement-based size distribution parameterizations in smoke plumes is essential to better constrain the climate and air quality effects of savannah and grassland fires.A substantial amount of secondary aerosols form within hours of biomass burning in southern African savannah and grassland fires, according to analyses of 5.5 years of continuous field measurements.

Characteristics of particle emissions and their atmospheric dilution during co-combustion of coal and wood pellets in a large combined heat and power plant

Abstract Coal combustion is one of the most significant anthropogenic CO2 and air pollution sources globally. This paper studies the atmospheric emissions of a power plant fuelled with a mixture of industrial pellets (10.5%) and coal (89.5%). Based on the stack measurements, the solid particle number emission, which was dominated by sub-200 nm particles, was 3.4×1011 MJ-1 for the fuel mixture when electrostatic precipitator (ESP) was cleaning the flue gas. The emission factor was 50 mg MJ-1 for particulate mass and 11 740 ng MJ-1 for the black carbon with the ESP. In the normal operation situation of the power plant, i.e., including the flue-gas desulphurisation and fabric filters (FGD and FF), the particle number emission factor was 1.7×108 MJ-1, particulate mass emission factor 2 mg MJ-1 and black carbon emission factor 14 ng MJ-1. Transmission electron microscopy (TEM) analysis supported the particle number size distribution measurement in terms of particle size and the black carbon concentration. The TEM images of the particles showed variability of the particle sizes, morphologies and chemical compositions. The atmospheric measurements, conducted in the flue-gas plume, showed that the flue-gas dilutes closed to background concentrations in 200 sec. However, an increase in particle number concentration was observed when the flue gas aged. This increase in particle number concentration was interpret as formation of new particles in the atmosphere. In general, the study highlights the importance of detailed particle measurements when utilizing new fuels in existing power plants. Implications: CO2 emissions of energy production decrease when substituting coal with biofuels. The effects of fuels changes on particle emission characteristics have not been studied comprehensively. In this study conducted for a real-scale power plant, co-combustion of wood pellets and coal caused elevated black carbon emissions. However, it was beneficial from the total particle number and particulate mass emission point of view. Flue-gas cleaning can significantly decrease the pollutant concentrations but also changes the characteristics of emitted particles. Atmospheric measurements implicated that the new particle formation in the atmospheric flue-gas plume should be taken into account when evaluating all effects of fuel changes.” Are implication statements part of the manuscript?