First online measurements of sulfuric acid gas in modern heavy-duty diesel engine exhaust: implications for nanoparticle formation

To mitigate the diesel particle pollution problem, diesel vehicles are fitted with modern exhaust after-treatment systems (ATS), which efficiently remove engine-generated primary particles (soot and ash) and gaseous hydrocarbons. Unfortunately, ATS can promote formation of low-vapor-pressure gases, which may undergo nucleation and condensation leading to formation of nucleation particles (NUP). The chemical nature and formation mechanism of these particles are only poorly explored. Using a novel mass spectrometric method, online measurements of low-vapor-pressure gases were performed for exhaust of a modern heavy-duty diesel engine operated with modern ATS and combusting low and ultralow sulfur fuels and also biofuel. It was observed that the gaseous sulfuric acid (GSA) concentration varied strongly, although engine operation was stable. However, the exhaust GSA was observed to be affected by fuel sulfur level, exhaust after-treatment, and driving conditions. Significant GSA concentrations were measured also when biofuel was used, indicating that GSA can be originated also from lubricant oil sulfur. Furthermore, accompanying NUP measurements and NUP model simulations were performed. We found that the exhaust GSA promotes NUP formation, but also organic (acidic) precursor gases can have a role. The model results indicate that that the measured GSA concentration alone is not high enough to grow the particles to the detected sizes.

Facing the key workplace challenge: assessing and preventing exposure to nanoparticles at source

Nanomaterials present new challenges to understanding, predicting, and managing potential health risks in occupational environments. In this study, we characterize the key physical processes related to formation and growth of nanoparticles. The main focus is on various occupational environments, as these are known to be major environments with nanoparticles in indoor air. The protection of people potentially to be exposed to nanoparticles is one of the key issues in terms of risk assessment and prevention. Two of the main protection techniques that are discussed and characterized are ventilation and filtration, which are widely used in practical applications.

Regulation of nicotinic receptors in the brain of mice withdrawn from chronic oral nicotine treatment

The effect of nicotine withdrawal on regional regulation of brain nicotinic receptors was studied in mice after chronic administration of nicotine in the drinking water for 2, 4 or 7 weeks. Two weeks of chronic nicotine administration did not alter the binding of [3H]-nicotine in the midbrain, cortex or cerebellum of the mice, while after both 4-and 7-week treatments a significant increase in the specific [3H]-nicotine binding was observed in cortical and midbrain membranes. In the midbrain, the [3H]-nicotine binding was increased by about 40% in mice withdrawn for 48-72 h from the 4-week chronic nicotine treatment and in mice withdrawn for 48 h from the 7-week treatment. The [3H]-nicotine binding was significantly increased (by 55-65%) in the cortex at 48 h and 72 h after withdrawal from 4-week chronic nicotine and it was even somewhat more increased (by 72-66%) after 7-week treatment. The cortical [3H]-nicotine binding was not altered at 24 h after the 4-week treatment, but in mice withdrawn for 24 h from the 7-week treatment it was increased by 116%. The increases in [3H]-nicotine binding returned to control levels within 1 week after withdrawal. None of the studied treatments affected the [3H]-nicotine binding in the cerebellum. Tolerance towards nicotine-induced locomotor depression was only found in mice withdrawn for 24 h from the 7-week chronic nicotine administration. These findings suggest that at least 4-week chronic nicotine administration in the drinking water is needed before any upregulation of nicotinic receptors can be observed. Furthermore, in our experiments the increase in the [3H]-nicotine binding was seen before behavioural tolerance could be demonstrated. The differences between brain regions in the time course of nicotinic receptor upregulation may reflect variations in nicotinic receptor subunits and their sensitivity to chronic nicotine treatment.