Tuukka Petäjä

Identification and quantification of particle growth channels during new particle formation

Atmospheric new particle formation (NPF) is a key source of ambient ultrafine particles that may contribute substantially to the global production of cloud condensation nuclei (CCN). While NPF is driven by atmospheric nucle- ation, its impact on CCN concentration depends strongly on atmospheric growth mechanisms since the growth rate must exceed the loss rate due to scavenging in order for the parti- cles to reach the CCN size range. In this work, chemical com- position measurements of 20 nm diameter particles during NPF in Hyytiala, Finland, in March-April 2011 permit iden- tification and quantitative assessment of important growth channels. In this work we show the following: (A) sulfuric acid, a key species associated with atmospheric nucleation, accounts for less than half of particle mass growth during this time period; (B) the sulfate content of a growing parti- cle during NPF is quantitatively explained by condensation of gas-phase sulfuric acid molecules (i.e., sulfuric acid up- take is collision-limited); (C) sulfuric acid condensation sub- stantially impacts the chemical composition of preexisting nanoparticles before new particles have grown to a size suffi- cient to be measured; (D) ammonium and sulfate concentra- tions are highly correlated, indicating that ammonia uptake is driven by sulfuric acid uptake; (E) sulfate neutralization by ammonium does not reach the predicted thermodynamic end point, suggesting that a barrier exists for ammonia up- take; (F) carbonaceous matter accounts for more than half of the particle mass growth, and its oxygen-to-carbon ratio ( 0.5) is characteristic of freshly formed secondary organic aerosol; and (G) differences in the overall growth rate from one formation event to another are caused by variations in the growth rates of all major chemical species, not just one individual species.

Hygroscopicity of sub-6 nm sodium chloride particles

We measured the hygroscopic growth of Sodium Chloride particles in a size range from 2.5 nm to 6 nm in a relative humidities ranging from 10% to 95% with a nano hygroscopicity tandem differential mobility analyzer The aim of this study was to investigate how accurately the Kohler theory describes the hygroscopic growth of particles with a diameter of few nanometers.

Characterization of diethylene glycol-condensation particle counters for detection of sub-3 nm particles

The counting efficiencies of 2 different types of diethylene-glycol (DEG) based Condensation Particle Counters (CPCs) is described and discussed. The development of two laminar flow CPCs, sensitive in the size range below 3 nm is described. The two types used are a modified TSI 3776 laminar diffusion-type CPC operating with DEG instead of butanol (DEG-CPC) and a turbulent mixing Particle Size Magnifier (PSM) A09 from Airmodus. For each of the two types two different systems with slightly different settings have been investigated, respectively. The two laminar flow CPCs were operated at different temperature settings, where one of the mixing type systems was running at a fixed saturation ratio and therefore had a fixed cut-off diameter and the other one was opaerated in scanning mode. Various different test aerosols have been generated to obtain cut-off curves for all four different CPCs. The main focus was on measuring the counting efficiencies under well controlled laboratory conditions. Therefore a high...

Long-term size-segregated cloud condensation nuclei counter (CCNc) measurements in a boreal environment and the implications for aerosol-cloud interactions

Ambient aerosol CCN and hygroscopic properties were measured with a size-segregated CCNc in a boreal environment of Southern Finland at the SMEAR II station since February 2009. The overall median critical diameter Dc for CCN activation is reported at 75 nm, exhibiting a clear maximum in February and a minimum in July. The overall median aerosol hygroscopicity parameter κ is reported at 0.22, indicating that ambient aerosol in Hyytiala is less hygroscopic than the global continental and European continental averages. It is, however, more hygroscopic than ambient aerosol in an Amazon rainforest, the European high alpine site or the mountainous forest. The low hygroscopicity in the boreal forest is attributed to a large organic fraction present in the aerosol mass comparative to other locations within Europe. Aerosol mass spectrometer (AMS) data were used to demonstrate a positive correlation between κ and sulphate and ammonia, and a negative correlation between κ and the organic mass fraction. No distingui...

Measuring composition and growth of ion clusters of sulfuric acid, ammonia, amines and oxidized organics as first steps of nucleation in the CLOUD experiment

The mechanisms behind the nucleation of vapors forming new particles in the atmosphere had been proven difficult to establish. One main aim of the CLOUD experiment was to explore in detail these first steps of atmospheric new particle formation by performing extremely well controlled laboratory experiments. We examined nucleation and growth in the presence of different mixtures of vapors, including sulfuric acid, ammonia, dimethylamine, and oxidation products of pinanediol or α-pinene. Among the employed state-of-the-art instrumentation, a high-resolution mass spectrometer that directly sampled negatively charged ions and clusters proved particularly useful. We were able to resolve most of the chemical compositions found for charged sub-2nm clusters and to observe their growth in time. These compositions reflected the mixture of condensable vapors in the chamber and the role of each individual vapor in forming sub-2nm clusters could be explored. By inter-comparing between individual experiments and ambient observations, we try to establish which vapors participate in nucleation in the actual atmosphere, and how.

Evolution of α-pinene oxidation products in the presence of varying oxidizers: Negative APi-TOF point of view

Laboratory experiments conducted in the frame of the CLOUD project at CERN investigated the oxidation of α-pinene oxidation products in a carefully controlled environment and with different oxidation conditions: 1) pure ozonolysis (with the use of an hydroxyl radical (⋅OH) scavenger), 2) ozonolysis without use of a scavenger, and 3) pure ⋅OH oxidation using nitrous acid (HONO) to produce ⋅OH. The anions and negatively charged clusters present in the chamber were analyzed and their chemical composition compared for the different oxidation pathways.

Sulphur dioxide and sulphuric acid concentrations in the vicinity of Kilpilahti industrial area

Industrial activity is a major source of sulphur compound emissions. The sulphuric acid and sulphur dioxide measurements in the vicinity of the industrial area and the oil refinery in Kilpilahti expressed great variation in concentration. The hourly mean values of concentration were categorized according to the area from where the air mass was travelling towards the measurement site. The statistical characteristics and diurnal behavior of emissions between these areas were significantly different.

Laboratory characterization of a size-resolved CPC battery to infer the composition of freshly formed atmospheric nuclei

A size-resolved condensation particle counter battery (SR-CPCb) was developed to infer the composition of freshly nucleated aerosol down to 1 nm in diameter. This was accomplished by exploiting the strong dependence of CPC counting efficiency on particle composition and CPC working fluid. The SR-CPCb consists of CPCs that are optimized for sub 2 nm particle detection using the following working fluids: diethylene glycol, water, and butanol. Laboratory characterizations of the SR-CPCb were performed for challenge aerosols of various compositions down to 1 nm in diameter.

Climatic implications of the Brazilian biofuel transition

A global climate model is being run to study the consequences of Brazil transitioning from fossil to biofuels over the next few decades. Assuming all other factors constant, preliminary results suggest little to no climatic relevance.

Effect of salt formation on condensation of organic compounds on atmospheric nanoparticles

Freshly formed atmospheric nanoparticles have been observed to contain also such organic compounds which have too high saturation vapor pressure to condense on nanoparticles reversibly. The condensation of these compounds on the particles may be facilitated by particle phase processes that transform the compounds into less-volatile form. Here we use particle growth model MABNAG to study the effect of particle phase acid-base chemistry on the condensation of organic acids and bases.