Mayeesha F. Rahim

Bio: Mayeesha F. Rahim is an academic researcher from McGill University. The author has contributed to research in topics: Aerosol. The author has an hindex of 1, co-authored 1 publications receiving 20 citations.

Lowering the Size Detection Limits of Ag and TiO2 Nanoparticles by Single Particle ICP-MS.

Abstract: As the production and use of engineered nanomaterials increase, there is an urgent need to develop analytical techniques that are sufficiently sensitive to be able to measure the very small nanopar...

A Review of the Representation of Aerosol Mixing State in Atmospheric Models

Abstract: Aerosol mixing state significantly affects concentrations of cloud condensation nuclei (CCN), wet removal rates, thermodynamic properties, heterogeneous chemistry, and aerosol optical properties, with implications for human health and climate. Over the last two decades, significant research effort has gone into finding computationally-efficient methods for representing the most important aspects of aerosol mixing state in air pollution, weather prediction, and climate models. In this review, we summarize the interactions between mixing-state and aerosol hygroscopicity, optical properties, equilibrium thermodynamics and heterogeneous chemistry. We focus on the effects of simplified assumptions of aerosol mixing state on CCN concentrations, wet deposition, and aerosol absorption. We also summarize previous approaches for representing aerosol mixing state in atmospheric models, and we make recommendations regarding the representation of aerosol mixing state in future modelling studies.

Composition and morphology of particle emissions from in-use aircraft during takeoff and landing

Abstract: In order to provide realistic data for air pollution inventories and source apportionment at airports, the morphology and composition of ultrafine particles (UFP) in aircraft engine exhaust were measured and characterized. For this purpose, two independent measurement techniques were employed to collect emissions during normal takeoff and landing operations at Brisbane Airport, Australia. PM1 emissions in the airfield were collected on filters and analyzed using the particle-induced X-ray emission (PIXE) technique. Morphological and compositional analyses of individual ultrafine particles in aircraft plumes were performed on silicon nitride membrane grids using transmission electron microscopy (TEM) combined with energy-dispersive X-ray microanalysis (EDX). TEM results showed that the deposited particles were in the range of 5 to 100 nm in diameter, had semisolid spherical shapes and were dominant in the nucleation mode (18 – 20 nm). The EDX analysis showed the main elements in the nucleation particles were C, O, S and Cl. The PIXE analysis of the airfield samples was generally in agreement with the EDX in detecting S, Cl, K, Fe and Si in the particles. The results of this study provide important scientific information on the toxicity of aircraft exhaust and their impact on local air quality.

Quantification and Characterization of Ti-, Ce-, and Ag-Nanoparticles in Global Surface Waters and Precipitation.

Abstract: Nanoparticle (NP) emissions to the environment are increasing as a result of anthropogenic activities, prompting concerns for ecosystems and human health. In order to evaluate the risk of NPs, it is necessary to know their concentrations in various environmental compartments on regional and global scales; however, these data have remained largely elusive due to the analytical difficulties of measuring NPs in complex natural matrices. Here, we measure NP concentrations and sizes for Ti-, Ce-, and Ag-containing NPs in numerous global surface waters and precipitation samples, and we provide insights into their compositions and origins (natural or anthropogenic). The results link NP occurrences and distributions to particle type, origin, and sampling location. Based on measurements from 46 sites across 13 countries, total Ti- and Ce-NP concentrations (regardless of origin) were often found to be within 104 to 107 NP mL-1, whereas Ag NPs exhibited sporadic occurrences with low concentrations generally up to 105 NP mL-1. This generally corresponded to mass concentrations of <1 ng L-1 for Ag-NPs, <100 ng L-1 for Ce-NPs, and <10 μg L-1 for Ti-NPs, given that measured sizes were often below 15 nm for Ce- and Ag-NPs and above 30 nm for Ti-NPs. In view of current toxicological data, the observed NP levels do not yet appear to exceed toxicity thresholds for the environment or human health; however, NPs of likely anthropogenic origins appear to be already substantial in certain areas, such as urban centers. This work lays the foundation for broader experimental NP surveys, which will be critical for reliable NP risk assessments and the regulation of nano-enabled products.

Single- and Multi-Element Quantification and Characterization of TiO2 Nanoparticles Released From Outdoor Stains and Paints

Abstract: With growing applications of TiO2 nanoparticles (NPs) in outdoor surface coatings, notably in paints and stains, their release into the environment is inevitable This work measured NPs released from painted and stained surfaces and characterized them by size and composition using magnetic sector single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) and SP-ICP-time-of-flight-MS (SP-ICP-TOF-MS) Two in situ experimental plans were examined in which natural precipitation interacted with nano-enhanced surfaces to varying degrees during the fall and winter Weathering data showed that longer contact times of the precipitation (snow and rain) resulted in greater NP release Although the stained surfaces had far fewer NPs per unit area, they lost a much higher fraction of their NP load (max 6% leached, as opposed to <10-4 % in paints), over similar exposure times NP release was particularly enhanced for conditions of frequent rainfall and spring snow melt (ie slushy snow) SP-ICP-TOF-MS measurements on the Ti NPs indicated that they were often associated with a secondary metal in both the liquid paint (Al was detected in 20% of the Ti NPs; Zr in about 1% of the NP) and the liquid stain (Fe was detected in 7%, Si in 8% and Al in 3 % of the Ti NPs) In contrast, for the vast majority of Ti NPs being leached out of the painted/stained surfaces, only Ti was detected Metal interactions in the paint were explained by binding of the TiO2 within a complex paint matrix; while in the stain, TiO2 NPs were hypothesized to be found in heteroagglomerates, potentially with aluminosilicates (Fe, Si and Al) In rain and snow, Ti was the only element detected in about half of the Ti NPs; in the other half, Ti often co-occurred with Fe, Si and Al The results indicate that single element, likely anthropogenic, Ti NPs are already prevalent in the natural precipitation and that NP release from surface coatings will further increase their presence in the environment