Annual particle flux observations over a heterogeneous urban area

Long-term eddy covariance particle number flux measurements for the diameter range 6 nm to 5 μm were performed at the SMEAR III station over an urban area in Helsinki, Finland. The heterogeneity of the urban measurement location allowed us to study the effect of different land-use classes in different wind directions on the measured fluxes. The particle number fluxes were highest in the direction of a local road on weekdays, with a daytime median flux of 0.8×10<sup>9</sup> m<sup>−2</sup> s<sup>−1</sup>. The particle fluxes showed a clear dependence on traffic rates and on the mixing conditions of the boundary layer. The measurement footprint was estimated by the use of both numerical and analytical models. Using the crosswind integrated form of the footprint function, we estimated the emission factor for the mixed vehicle fleet, yielding a median particle number emission factor per vehicle of 3.0×10<sup>14</sup> # km<sup>−1</sup>. Particle fluxes from the vegetated area were the lowest with daytime median fluxes below 0.2×10<sup>9</sup> m<sup>−2</sup> s<sup>−1</sup>. During weekends and nights, the particle fluxes were low from all land use sectors being in the order of 0.02–0.1×10<sup>9</sup> m<sup>−2</sup> s<sup>−1</sup>. On an annual scale the highest fluxes were measured in winter, when emissions from stationary combustion sources are also highest. Particle number fluxes were compared with the simultaneously measured CO<sub>2</sub> fluxes and similarity in their sources was distinguishable. For CO<sub>2</sub>, the median emission factor of vehicles was estimated to be 370 g km<sup>−1</sup>

On the diurnal cycle of urban aerosols, black carbon and the occurrence of new particle formation events in springtime São Paulo, Brazil

Large conurbations are a significant source of the anthropogenic pollution and demographic differences between cities that result in a different pollution burden. The metropolitan area of São Paulo (MASP, population 20 million) accounts for one fifth of the Brazilian vehicular fleet. A feature of MASP is the amount of ethanol used by the vehicular fleet, known to exacerbate air quality. The study describes the diurnal behaviour of the submicron aerosol and relies on total particle number concentration, particle number size distribution, light scattering and light absorption measurements. Modelled planetary boundary layer (PBL) depth and air mass movement data were used to aid the interpretation. During morning rush-hour, stagnant air and a shallow PBL height favour the accumulation of aerosol pollution. During clear-sky conditions, there was a wind shift towards the edge of the city indicating a heat island effect with implications on particulate pollution levels at the site. The median total particle number concentration for the submicron aerosol typically varied in the range 1.6 × 10<sup>4</sup>–3.2 × 10<sup>4</sup> cm<sup>−3</sup> frequently exceeding 4 × 10<sup>4</sup> cm<sup>−3</sup> during the day. During weekdays, nucleation-mode particles are responsible for most of the particles by numbers. The highest concentrations of total particle number concentrations and black carbon (BC) were observed on Fridays. Median diurnal values for light absorption and light scattering (at 637 nm wavelength) varied in the range 12–33 Mm<sup>−1</sup> and 21–64 Mm<sup>−1</sup>, respectively. The former one is equal to 1.8–5.0 μg m<sup>−3</sup> of BC. The growth of the PBL, from the morning rush-hour until noon, is consistent with the diurnal cycle of BC mass concentrations. Weekday hourly median single-scattering albedo (ω<sub>0</sub>) varied in the range 0.59–0.76. Overall, this suggests a top of atmosphere (TOA) warming effect. However, considering the low surface reflectance of urban areas, for the given range of ω<sub>0</sub>, the TOA radiative forcing can be either positive or negative for the sources within the MASP. On the average, weekend ω<sub>0</sub> values were 0.074 higher than during weekdays. During 11% of the days, new particle formation (NPF) events occurred. The analysed events growth rates ranged between 9 and 25 nm h<sup>−1</sup>. Sulphuric acid proxy concentrations calculated for the site were less than 5% of the concentration needed to explain the observed growth. Thus, other vapours are likely contributors to the observed growth

Basic characteristics of atmospheric particles, trace gases and meteorology in a relatively clean Southern African Savannah environment

We have analyzed one year (July 2006–July 2007) of measurement data from a relatively clean background site located in dry savannah in South Africa. The annual-median trace gas concentrations were equal to 0.7 ppb for SO<sub>2</sub>, 1.4 ppb for NO<sub>x</sub>, 36 ppb for O<sub>3</sub> and 105 ppb for CO. The corresponding PM<sub>1</sub>, PM<sub>2.5</sub> and PM<sub>10</sub> concentrations were 9.0, 10.5 and 18.8 μg m<sup>−3</sup>, and the annual median total particle number concentration in the size range 10–840 nm was 2340 cm<sup>−3</sup>. During Easterly winds, influence of industrial sources approximately 150 km away from the measurement site was clearly visible, especially in SO<sub>2</sub> and NO<sub>x</sub> concentrations. Of gases, NO<sub>x</sub> and CO had a clear annual, and SO<sub>2</sub>, NO<sub>x</sub> and O<sub>3</sub> clear diurnal cycle. Atmospheric new-particle formation was observed to take place in more than 90% of the analyzed days. The days with no new particle formation were cloudy or rainy days. The formation rate of 10 nm particles varied in the range of 0.1–28 cm<sup>−3</sup> s<sup>−1</sup> (median 1.9 cm<sup>−3</sup> s<sup>−1</sup>) and nucleation mode particle growth rates were in the range 3–21 nm h<sup>−1</sup> (median 8.5 nm h<sup>−1</sup>). Due to high formation and growth rates, observed new particle formation gives a significant contribute to the number of cloud condensation nuclei budget, having a potential to affect the regional climate forcing patterns

Airborne measurements over the boreal forest of southern Finland during new particle formation events in 2009 and 2010

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New foliage growth is a significant, unaccounted source for volatiles in boreal evergreen forests

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Position Models and Language Modeling

International audienceIn statistical language modelling the classic model used is $n$-gram. This model is not able however to capture long term dependencies, \emph{i.e.} dependencies larger than $n$. An alternative to this model is the probabilistic automaton. Unfortunately, it appears that preliminary experiments on the use of this model in language modelling is not yet competitive, partly because it tries to model too long term dependencies. We propose here to improve the use of this model by restricting the dependency to a more reasonable value. Experiments shows an improvement of 45\% reduction in the perplexity obtained on the Wall Street Journal language modeling task

(Re)Conceptualizing decision-making tools in a risk governance framework for emerging technologies—the case of nanomaterials

The utility of decision-making tools for the risk governance of nanotechnology is at the core of this paper. Those working in nanotechnology risk management have been prolific in creating such tools, many derived from European FP7 and H2020-funded projects. What is less clear is how such tools might assist the overarching ambition of creating a fair system of risk governance. In this paper, we reflect upon the role that tools might and should play in any system of risk governance. With many tools designed for the risk governance of this emerging technology falling into disuse, this paper provides an overview of extant tools and addresses their potential shortcomings. We also posit the need for a data readiness tool. With the EUs NMP13 family of research consortia about to report to the Commission on ways forward in terms of risk governance of this domain, this is a timely intervention on an important element of any risk governance system

Vertical profiles of sub-3nm particles over the boreal forest

This work presents airborne observations of sub-3 nm particles in the lower troposphere and investigates new particle formation (NPF) within an evolving boundary layer (BL). We studied particle concentrations together with supporting gas and meteorological data inside the planetary BL over a boreal forest site in Hyytiala, southern Finland. The analysed data were collected during three flight measurement campaigns: May-June 2015, August 2015 and April-May 2017, including 27 morning and 26 afternoon vertical profiles. As a platform for the instrumentation, we used a Cessna 172 aircraft. The analysed flight data were collected horizontally within a 30 km distance from SMEAR II in Hyytiala and vertically from 100 m above ground level up to 2700 m. The number concentration of 1.5-3 nm particles was observed to be, on average, the highest near the forest canopy top and to decrease with increasing altitude during the mornings of NPF event days. This indicates that the precursor vapours emitted by the forest play a key role in NPF in Hyytiala. During daytime, newly formed particles were observed to grow in size and the particle population became more homogenous within the well-mixed BL in the afternoon. During undefined days with respect to NPF, we also detected an increase in concentration of 1.5-3 nm particles in the morning but not their growth in size, which indicates an interrupted NPF process during these undefined days. Vertical mixing was typically stronger during the NPF event days than during the undefined or non-event days. The results shed light on the connection between boundary layer dynamics and NPF.Peer reviewe