Removal of an airborne low volatility metal under fuel-rich and fuel lean conditions through condensation onto soot and/or sorbent particles.

The removal by a sorbent of a low volatility heavy metal, barium, from a combustor exhaust stream was investigated experimentally. The barium was introduced into the gas phase through a combustion process simulating incineration of waste materials. Sorbent- and metal-feed-rate, temperature and air intake were varied to study the impact on the gas-to-particle conversion and the metal condensation process. Peak temperature and subsequent temperature drop were found to be the dominant factors affecting the condensation process. Fuel-rich and fuel-lean conditions result in lower peak temperatures and a more rapid temperature drop relative to stoichiometric conditions. Since the metal vapor saturation pressure falls exponentially with temperature a larger condensation rate was observed, as long as nucleation was suppressed. Fuel-rich conditions promote the formation of soot particles. These particles function as sites for subsequent metal-species condensation. Chlorine was injected into the flow, to study the effect on metal vaporization. Chlorine promoted the volatilization of barium and therefore the subsequent condensation capture was made more effective.     

Air quality monitoring system using lichens as bioindicators in Central Argentina

Air quality studies with bioindicators have not been well developed in South America. In the city of Córdoba, there are not permanent air pollutant measurements by equipment. In order to develop an air quality biomonitoring system using lichens, we applied a systematic sampling in the city of Córdoba, Argentina. A total of 341 plots were sampled in the area of the city which is a square of 24 × 24 km. In each sample plot we selected three phorophytes and estimated the frequency and cover of lichen species growing at 1.5 m on trunks. We also calculated the Index of Atmospheric Purity (IAP) using lichen frequencies. Maps with number of lichen species, cover values, and IAP were performed. The lichen community was described with nine species where Physcia undulata and Physcia endochryscea were the most frequent. Moreover, these two species were dominant in the community with the highest cover index. The central area of the city is considered a lichen desert with poor air quality. The southeast and northwest areas of the city showed the highest IAP values and number of species. In general, the city shows fair air quality and few areas with good and very good air quality.     

Multi-level modelling of chlorination by-product presence in drinking water distribution systems for human exposure assessment purposes

During drinking water treatment and distribution, chlorine reacts with organic matter occurring in water to form various chlorination by-products (CBPs) such as trihalomethanes (THMs) and haloacetic acids (HAAs). This paper presents the occurrence of THMs and HAAs in different water distribution systems (DS) of the same region and their modelling for exposure assessment purposes. This study was conducted in eight DS supplying chlorinated water to the population of Québec City, Canada. These systems differ in type of water source (i.e. surface, ground or mixed water), in treatment applied at the plant, and in size and structure of the DS. Two spatio-temporal databases for THMs and HAAs were implemented, one for model development and the other for model validation. The analysis of the data demonstrates significant seasonal and spatial variations of these compounds. A multi-level statistical modelling approach was applied to estimate the ranges for occurrence of THMs and HAAs in the eight DS (i.e. a single model for the study region for each CBP species). The modelling approach integrates available or easily measurable parameters. For both THMs and HAAs, a two-level model considering a sampling-site random effect was selected among various models initially developed. The model capacity for estimating the presence of THMs and HAAs in drinking water and its usefulness for exposure assessment purposes in the studied region was demonstrated.