Abstract
Wherever measurements have been made bromoform was found to be ubiquitous in the surface ocean in pmolar-nmolar concentrations. These measurements show concentrations in coastal regions orders of magnitude higher than in the pelagic oceans. Its atmospheric presence is primarily due to its release from algae and rapid transport to the marine boundary troposphere where it is known to participate in ozone chemistry via photochemical and catalytic pathways. Until quite recently, a limited number of studies existed (compared to other marine volatile organic compounds (VOCs)), mainly due to the analytical challenge(s) presented by the low environmental mixing ratios. In this work we detail the development of a simplified, cost effective method to detect and quantify bromoform in environmental air samples. Air samples (1.5 L) were preconcentrated onto a precooled adsorbent (Carbopack X/Carboxen 1016) trap. These samples were injected by means of rapid thermal desorption for separation and detection by GC-ECD. The system was calibrated by means of a custom-built permeation oven. A linear system response was achieved, having a detection limit of 0.73 ± 0.09 ppt. A range of environmental samples was analysed to demonstrate the ability of the technique to separate and identify bromoform from air samples. The results showed that bromoform concentrations typically averaged 24.7 ± 17.3 ppt in marine air samples, 68.5 ± 26.3 ppt in Cape Town urban air samples and 33.9 ± 40.5 ppt in simulated biomass burning plumes (SBBP).
Highlights
Bromoform is a naturally occurring organohalogen found in the marine boundary layer as a result of production by phytoplankton [1,2], ice algae [3] and kelp (e.g., [4,5,6,7,8])
Quantitative trapping tests showed no significant breakthrough of bromoform with sample volumes up to 3 L at ambient temperatures, whereas significant breakthrough occurred at 5 L (Figure 7)
For more volatile compounds (unidentified but with constant retention times from 2–3 min), significant breakthrough was found to occur from 1 L. This implies that our method as described here is suitable for bromoform analysis within sample volumes of up to 3 L ; more work is needed to demonstrate whether this method is suitable for low molecular weight volatile halogenated organic compounds (VHOCs)
Summary
Bromoform is a naturally occurring organohalogen found in the marine boundary layer as a result of production by phytoplankton [1,2], ice algae [3] and kelp (e.g., [4,5,6,7,8]). Whereas there are some known anthropogenic sources of bromoform (e.g., water chlorination; coastal power generation) these sources are far smaller than natural sources when considered on a global scale [10]. Being volatile and not readily soluble in water bromoform readily crosses the sea-air boundary, resulting in significant Ppt) concentrations in the marine troposphere [11]. There is some evidence to suggest a significant local terrestrial source of bromoform to the troposphere off the N. W. coast of Africa [12], but this source has neither been identified nor quantified
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