Allan Gross

A study of new particle formation in the marine boundary layer over the central Arctic Ocean using a flexible multicomponent aerosol dynamic model

ABSTRACT Enhancement of number concentrations of particles with sizes less than 25 nm diameter has been frequently observed in the boundary layer over the central Arctic Ocean during summer. The sectional aerosol dynamics model for Marine Aerosol Formation (MAFOR) was applied to evaluate the capability of different nucleation mechanisms to reproduce nucleation events observed during three expeditions (1996, 2001 and 2008) onboard the Swedish icebreaker Oden. Model calculations suggest that a source rate of a condensable organic vapour (OV) of about 2×105 cm−3 s−1 is required to reproduce observed growth of nucleation mode particles. Nucleation rates predicted by the newly proposed combined sulphuric acid nucleation mechanism, which best described new particle formation in the Arctic, ranged from 0.04 to 0.1 cm−3 s−1. This mechanism additively combines ion-mediated nucleation and cluster activation, and treats condensation of OV without correction of the Kelvin effect. In several events, the simultaneous number enhancement of particles in the 20–50 nm size range remained unexplained by the nucleation mechanisms. This lends support to alternative theories such as the fragmentation of marine gels (≈200–500 nm diameter in size) by physical or chemical processes.

Theoretical Investigation of the Reaction between Carbonyl Oxides and Ammonia

The gas-phase reaction between carbonyl oxides and ammonia is investigated by quantum mechanical calculations. The density functional method B3LYP with the basis set 6-311++G(2d,2p) was employed for the geometry and energy optimization of the stationary points along the reaction path. The energies have been refined by CCSD(T) with various basis sets and Gaussian-3 level of theory. The reaction mechanisms are studied for three different carbonyl oxides, H2COO (methyl carbonyl oxide), CH3HCOO (ethyl carbonyl oxide), and (CH3)2COO (acetone carbonyl oxide). First, a prereactive complex is formed, where a hydrogen bond is formed between ammonia and the terminal oxygen atom in the COO moiety. Next, a structural rearrangement occurs, leading to the formation of a chemical bond between the nitrogen atom and the carbon in the COO moiety as well as a transfer of the hydrogen atom from nitrogen atom to the terminal oxygen atom in the COO moiety. The newly formed molecule is a hydroperoxide amine. All the studied reactions are exothermic. The estimated reaction rates range from 1.8 x 10(-13) to 6.9 x 10(-14) and to 5.1 x 10(-18) cm3 molecule(-1) s(-1) for H2COO, CH3HCOO, and (CH3)2COO, respectively. This shows that the investigated process are important in locations with intensive farming.

A new flexible multicomponent model for the study of aerosol dynamics in the marine boundary layer

A new sectional aerosol dynamics model, MAFOR, was developed with the focus to study nucleation in the marine boundary layer. Novel aspects of the model are (1) flexibility in the treatment of gas phase chemistry, (2) treatment of liquid phase chemistry, which can be extended according to needs and (3) simultaneous calculation of number and mass concentration distributions of a multicomponent aerosol as functions of time. Comparison with well-documented aerosol models (MONO32 and AEROFOR), a comprehensive data set on gas phase compounds, aerosol size distribution and chemical composition obtained during theA OE-96 (Arctic Ocean Expedition, 1996)was used to evaluate the model. Dimethyl sulphide decay during advection of an air parcel over the Arctic pack ice was well captured by the applied models and predicted concentrations of gaseous sulphuric acid and methane sulphonic acid range up to 1.0 × 106 cm−3 and 1.8 × 106 cm−3, respectively. Different nucleation schemes were implemented in MAFOR which allow the simulation of new particle formation. Modelled nucleation rates from sulphuric acid nucleation via cluster activation were up to 0.21 cm−3 s−1 while those from ion-mediated nucleationwere below 10−2 cm−3 s−1. Classical homogeneous binary and ternary nucleation theories failed to predict nucleation over the central Arctic Ocean in summer.

Average Case Analysis of Blocks Relocation Heuristics

We consider the Blocks Relocation Problem (BRP) where some blocks stored in stacks have to be removed and where the order in which the blocks are to be removed is given in advance. We are only allowed to remove a block on top of a stack or to relocate a block from the top of a stack to the top of another stack. The objective is to remove the blocks using a minimum number of relocations. We present a simple BRP heuristic similar to a heuristic presented by Caserta and Vos. Under certain assumptions on the stack capacity and the initial stack height, we formally show that the heuristic produces high quality solutions with high probability for large BRP instances. For any positive numbers e 1 and e 2 we show how the heuristic – under the assumptions mentioned above – can be used to construct a polynomial time algorithm that for any n solves a fraction of 1 − e 1 of all BRP instances of size n using no more than 1 + e 2 times the optimal number of relocations.

Using crowd sensed data as input to congestion model

Emission of airborne pollutants and climate gasses from the transport sector is a growing problem, both in industrialised and developing countries. Planning of urban transport system is essential to minimise the environmental, health and economic impact of congestion in the transport system. To get accurate and timely information on traffic congestion, and by extension information on air pollution, near real time traffic models are needed. We present in this paper an implementation of the Restricted Stochastic User equilibrium model, that is capable to model congestions for very large Urban traffic systems, in less than an hour. The model is implemented in an open source database system, for easy interface with GIS resources and crowd sensed transportation data.

The social acceptance of artificial photosynthesis: towards a conceptual framework

Advancements in artificial photosynthesis have the potential to radically transform how societies convert and use energy. Their successful development, however, hinges not only on technical breakthroughs, but also acceptance and adoption by energy users. This article introduces a conceptual framework enabling analysts, planners and even investors to determine environments where artificial photosynthesis may thrive, and those where it may struggle. Drawn from work looking at the barriers and acceptance of solar photovoltaic and wind energy systems, the article proposes that social acceptance has multiple dimensions—socio-political, community and market—that must be met holistically in order for investors and users to embrace new technologies. The article argues that any future market acceptance for artificial photosynthesis will depend upon the prevalence of nine factors, which create conducive environments; the lack of the conditions engenders environments where they will likely be rejected. The conditions are (i) strong institutional capacity; (ii) political commitment; (iii) favourable legal and regulatory frameworks; (iv) competitive installation and/or production costs; (v) mechanisms for information and feedback; (vi) access to financing; (vii) prolific community and/or individual ownership and use; (viii) participatory project siting; and (ix) recognition of externalities or positive public image.

Probabilistic Analysis of Online Stacking Algorithms

Consider the situation where some items arrive to a storage location where they are temporarily stored in bounded capacity LIFO stacks until their departure. We consider the problem of deciding where to put an arriving item with the objective of using as few stacks as possible. The decision has to be made as soon as an item arrives and we assume that we only have information on the departure times for the arriving item and the items currently at the storage area. We are only allowed to put an item on top of another item if the item below departs at a later time. We assume that the numbers defining the storage time intervals are picked independently and uniformly at random from the interval [0, 1]. We present a simple polynomial time online algorithm for the problem and prove the following: For any positive real numbers \(\epsilon _1, \epsilon _2 > 0\) there exists an \(N > 0\) such that the algorithm uses no more than \((1+\epsilon _1)OPT\) stacks with probability at least \(1-\epsilon _2\) if the number of items is at least N where OPT denotes the optimal number of stacks. The result even holds if the stack capacity is \(o(\sqrt{n})\) where n is the number of items.

Pilot Study of Contaminants near Station Nord, a Military Airbase and Research Station in NE Greenland

There are very few studies of contaminants in waters, sediments and air in the vicinity of high Arctic military bases. This pilot study was commissioned by the Royal Danish Air Force and conducted around Station Nord, a small remote Danish Air Base and military station in northern Greenland, with the aim of determining the importance of local sources versus long range transport of contaminants. Trace metals (including As, Hg, Cd and Pb) were measured in freshwater and marine sediment cores, seawater and air within 3 km of the base. Concentrations of trace metals (including As, Hg, Cd and Pb) were analysed in the marine and freshwater sediment cores. Furthermore, air pollutants were measured to quantify emissions from local point sources compared to long range transport. All trace metals except As showed low concentrations in both a lake (Sommersoen) and in the sea (the Wandel Sea). As was found to be higher than expected both in marine and lake sediments. The concentrations of certain heavy metals were higher than would be expected from an undisturbed remote location. At present, there is not yet enough information to distinguish between local sources and long range transport as concentrations were found to be higher than expected both in marine and lake sediments. Some of this could be explained from the lithology but a major part of the variability remains unattributed and needs further study, though it is certainly possible that the concentrations were due to local sources and rubbish disposal practice.