(6gd) Toward Understanding the Atmospheric Chromium Chemistry

Amouei Torkmahalleh, M. - Presenter, Chemical Engineering Program, Middle East Technical University Northern Cyprus Campus

Trivalent chromium (Cr(III)) and hexavalent chromium (Cr(VI)) are the two common oxidation states of chromium in the environment. Inhalation exposure to Cr (VI) may lead to cancer, nasal damage, asthma and bronchitis. In contrast, Cr(III) is a trace element essential for the proper function of living organisms. Therefore, it is important to accurately discriminate between these two species in atmospheric particulate matter (PM) samples. In the United States, Cr(VI) is one of the criteria pollutants which has been monitored through the National Air Toxics Trends Station (NATTS) Network. Thus, measurement of Cr(VI), is one of the focal points for hazardous air pollutants (HAPs) monitoring in the US.

The focus of my PhD research at Clarkson University was centered around understanding the atmospheric chromium chemistry and improving the sampling of atmospheric Cr(VI). Chromium is available as soluble or insoluble in the atmosphere. When soluble chromium is dissolved in water, the transformation of Cr(VI) is expected to take place in the water associated with particles (aqueous chemistry of chromium). Airborne particles that include soluble salts like ammonium sulfate or ammonium nitrate can spontaneously take up water (deliquescence) from the air and form a solution on the surface of the particle. This liquid layer allows chemistry to take place. I have shown that keeping the sampling particulate matter below the point at which it can take up water provides significant improvements in the amount of Cr(VI) retained in the sample. I have found that Cr(III) is converted to Cr(VI) in the presence of gaseous species like ozone and reactive oxygen species (ROS) at dry condition (gas-solids chemistry of chromium) implying that Cr(III) conversion can produce false positive measurements for Cr(VI) sampling. I have demonstrated that conversion decreases at lower temperature values. Thus, based on my work, it is likely that a sampler that keeps the sample dry and cool will improve the recovery of Cr(VI) that is present in the sample. I built a prototype sampler and deployed 4 of them in a field study in NJ, side-by-side with 4 of the samplers currently used by USEPA in their HAPs monitoring network. These tests showed that the improved samplers did provide better preservation of Cr(VI).

Presently, I aim to develop a dynamic model for the simulation of aqueous chromium chemistry in the atmosphere (1<pH<5) and during the sampling period (24 hours- pH 9).

Recent studies showed that insoluble Cr(III) and insoluble Cr(VI) dominate atmospheric chromium mass. Regardless of few data in my PhD thesis, no information is available in the literature on the reaction kinetics of insoluble chromium speciation in airborne particles. Therefore my future research will concentrate on insoluble chromium chemistry (gas-solids chemistry of chromium) in the atmosphere (within next five years). My long term research plan (beyond next five years) is to investigate the chemistry/toxicity of soluble and insoluble chromium compounds in human lungs and their impact on lung surfactants. I have proposed three projects on atmospheric chromium. The first project investigates the reaction kinetics of insoluble Cr(III) and insoluble Cr(VI) with reactive oxygen species and volatile organic compounds, respectively (gas-solids reactions). The second project is aimed at designing and field testing a new Cr(VI) sampler to preserve both Cr(VI) and Cr(III) during sampling. The third project focuses on modeling Cr reactions (soluble and insoluble reactions) in the atmosphere and during the sampling. The details of my future research plan and potential funding agencies, current research, previous teaching and undergraduate research mentoring experiences are available during the AIChE  “Meet the Faculty Candidates” poster session.