K. G. Anlauf

Arctic springtime depletion of mercury

The Arctic ecosystem is showing increasing evidence of contamination by persistent, toxic substances, including metals such as mercury, that accumulate in organisms. In January 1995, we began continuous surface-level measurements of total gaseous mercury in the air at Alert, Northwest Territories, Canada (82.5° N, 62.5° W). Here we show that, during the spring (April to early June) of 1995, there were frequent episodic depletions in mercury vapour concentrations, strongly resembling depletions of ozone in Arctic surface air, during the three-month period following polar sunrise (which occurs in March),.

The Arctic: a sink for mercury

Mercury is a persistent, toxic and bio-accumulative pollutant of global interest. Its main mass in the troposphere is in the form of elemental gas-phase mercury. Rapid, near-complete depletion of mercury has been observed during spring in the atmospheric boundary layer of frozen marine areas in Arctic, sub-Arctic and Antarctic locations. It is strongly correlated with ozone depletion. To date, evidence has indicated strongly that chemistry involving halogen gases from surface sea-salt is the mechanism of this destruction. Precisely which halogen gases are the main players has remained unresolved. Our novel kinetic data and multiscale modelling show that Br atoms and BrO radicals are the most effective halogens driving mercury oxidation. The reduction of oxidized mercury deposited in the snow pack back to Hg0 and subsequent diffusion to the atmosphere is observed. However, it cannot compensate for the total deposition, and a net accumulation occurs. We use a unique global atmospheric mercury model to estimate that halogen-driven mercury depletion events result in a 44% increase in the net deposition of mercury to the Arctic. Over a 1-yr cycle, we estimate an accumulation of 325 tons of mercury in the Arctic.

A study of relationships between isoprene, its oxidation products, and ozone, in the Lower Fraser Valley, BC

As part of the Pacific 93 Oxidant Study that took place in the summer in the Lower Fraser Valley of British Columbia, we conducted measurements of isoprene, and its oxidation products methyl vinyl ketone (MVK) and methacrolein (MACR) at a surface site about 40 km east of the city of Vancouver. Hourly measurements were conducted between 16 July and 10 August 1993. The data indicated evidence for substantial contributions of isoprene chemistry to the production of ozone during oxidant episodes in this region. Maximum concentrations of isoprene, MVK, and MACR were 5.3, 2.0, and 1.0 ppb, resp., for 4 August. Analysis of the relationship between MVK and 03 during the oxidant episode period l–6 August led to an estimated contribution of isoprene chemistry of ozone production of ⩾ 13%. The average measured ratio of MVK/MACR was about 1.9–2.0 in the daytime, compared to the published relative yield of 1.4. Comparison of the MVK and MACR measurements to those of organic nitrates led to the conclusion that there is a significant non-photochemical source of MVK and MACR in this urban area.

Measurements of photolyzable chlorine and bromine during the Polar Sunrise Experiment 1995

We report measurements of rapidly photolyzable chlorine (Clp; e.g., Cl2 And HOCl) and bromine (Brp; e.g., Br2 and HOBr) in the high Arctic using a newly developed photoactive halogen detector (PHD). Ground level ambient air was sampled daily from mid-February through mid-April in the Canadian Arctic at Alert, Northwest Territories (82.5°N, 62.3°W), as part of the Polar Sunrise Experiment (PSE) 1995. Concentrations of “total photolyzable chlorine” varied from <9 to 100 pptv as Cl2 and that of “total photolyzable bromine” from <4 to 38 pptv as Br2. High concentration episodes of chlorine were observed only prior to sunrise (March 21), while high concentration episodes of bromine were measured throughout the study. The high concentrations of photolyzable chlorine and bromine prior to sunrise suggest a “dark” production mechanism that we assume yields Cl2 and Br2. An inverse correlation of bromine with ozone is clearly present in one major ozone depletion episode at the end of March. A trajectory analysis, taken with the differences in measured levels of photolyzable chlorine and bromine after sunrise, imply different production mechanisms for these two types of species. A steady state analysis of the data for one ozone depletion episode suggests a [Br]/[Cl] ratio in the range 100–300. The high concentrations of photolyzable bromine after sunrise imply the existence of a precursor other than aerosol bromide.

Relationships between organic nitrates and surface ozone destruction during Polar Sunrise Experiment 1992

Concurrent measurements of total reactive odd nitrogen species (i.e., NOy) and its major components, including organic nitrates, were carried out during 1992 Polar Sunrise Experiment (PSE92) at Alert, Northwest Territories, Canada, to investigate the episodic depletion of surface level ozone following polar sunrise. A series of C3-C7 alkyl nitrates formed from the atmospheric oxidation of hydrocarbons was measured daily during the 13-week study period (January 22 to April 22). In addition, a large number of gas chromatography/electron capture detector (GC/ECD) peaks with retention times greater than those of the hexyl nitrates were also identified as species containing −ONO2 group(s), using a nitrogen specific detector. The total concentrations of these organic nitrates ranged from 34 to 128 parts per trillion by volume and the distribution in the dark period was found to be similar to that found for rural lower-latitude air masses. In contrast to observations made at lower latitudes where alkyl nitrates make a relatively small contribution to NOy, the organic nitrates at Alert were found to contribute between 7 and 20% of the total odd nitrogen species. After polar sunrise the total concentrations of these organic nitrates decreased steadily, due primarily to the consumption of larger (>C4) alkyl nitrates. The C3 alkyl nitrate concentrations showed little variation during this study. During ozone depletion episodes in April there was a positive correlation between the concentration of the larger organic nitrates and ozone. Most surprisingly, the ratio of concentrations of isomeric alkyl nitrates with carbon numbers ≥5, and in particular those involving the C5 isomers, was found to show substantial variations coinciding with the O3 depletion events. This change in the isomeric alkyl nitrate ratios implies a substantial chemical processing of the air masses exhibiting ozone depletion. The possible mechanisms, which must involve consumption of the organic nitrates by either OH radicals or Cl atoms, are discussed in the context of the chemical and meteorological observations conducted at Alert during these ozone depletion events.

Ozone in the Arctic lower troposphere during winter and spring 2000 (ALERT2000)

Abstract A summary of the temporal and vertical characteristics of ozone in the Arctic boundary layer as observed during winter and spring 2000 near Alert, Nunavut, Canada (82°N, 62°W) is presented. The measurements were made during the Polar Sunrise Experiments ALERT2000. Particular attention is given to identifying chemical and atmospheric characteristics of short-lived (

Atmospheric chemistry of formaldehyde in the Arctic troposphere at Polar Sunrise, and the influence of the snowpack

The role of formaldehyde in the atmospheric chemistry of the Arctic marine boundary layer has been studied during both polar day and night at Alert, Nunavut, Canada. Formaldehyde concentrations were determined during two separate field campaigns (PSE 1998 and ALERT2000) from polar night to the light period. The large differences in the predominant chemistry and transport issues in the dark and light periods are examined here. Formaldehyde concentrations during the dark period were found to be dependent on the transport of air masses to the Alert site. Three regimes were identified during the dark period, including background (free-tropospheric) air, transported polluted air from Eurasia, and halogen-processed air transported across the dark Arctic Ocean. In the light period, background formaldehyde levels were compared to a calculation of the steady-state formaldehyde concentrations under background and low-ozone conditions. We found that, for sunlit conditions, the ambient formaldehyde concentrations cannot be reproduced by known gas-phase chemistry. We suggest that snowpack photochemistry contributes to production and emission of formaldehyde in the light period, which could account for the high concentrations observed at Alert.

Serial gas chromatographic/mass spectrometric measurements of some volatile organic compounds in the Arctic atmosphere during the 1992 Polar Sunrise Experiment

Variations of selected volatile organic compounds (11 halocarbons, 3 hydrocarbons, and acetone) in Arctic air were measured with an automated GC/MS at Alert, Canada, as a part of the 1992 Polar Sunrise Experiment. During the springtime ozone depletion, several volatile organic compounds (VOCs) correlated significantly with ozone. In particular, trichloroethylene had a strong positive correlation (R = 0.90), while bromoform (R = −0.87) and acetone (R = −0.90) were negatively correlated. Isopentane (R = 0.77), n-butane (R = 0.77), and tetrachloroethylene (R = 0.66) were also positively correlated with ozone. These findings suggest that the ozone depletion at Alert, including its small-scale fluctuations, is caused by the advection of air masses in which reactions by Cl and Br atoms rapidly consumed chloroethylenes and alkanes concurrently and destroyed ozone while the air was over the ocean. In winter, however, slightly negative correlations of ozone with trichloroethylene (R = −0.51) and tetrachloroethylene (R = −0.40) were found, which may be caused by the vertical mixing of surface and free tropospheric air.

Measurements of C2‐C7 hydrocarbons during the Polar Sunrise Experiment 1994: Further evidence for halogen chemistry in the troposphere

Air samples for nonmethane hydrocarbon (NMHC) analysis were collected at two ground-based sites: Alert, Northwest Territories (82.5°N, 62.3°W) and Narwhal ice camp, an ice floe 140 km northwest of Alert, from Julian days 90 to 117, 1994, and on a 2-day aerial survey conducted on Julian days 89 and 90, 1994 over the Arctic archipelago. Several ozone depletion events and concurrent decreases in hydrocarbon concentrations relative to their background levels were observed at Alert and Narwhal ice camp. At Narwhal, a long period (≥7 days) of ozone depletion was observed during which a clear decay of alkane concentration occurred. A kinetic analysis led to a calculated Cl atom concentration of 4.5×103 cm−3 during this period. Several low-ozone periods concurrent with NMHC concentration decreases were observed over a widespread region of the Arctic region (82°–85°N, and 51°–65°W). Hydrocarbon measurements during the aerial survey indicated that the low concentrations of these species occurred only in the boundary layer. In all ozone depletion periods, concentration changes of alkanes and toluene were consistent with Cl atom reactions. The changes in ethyne concentration from its background level were in excess of those expected from Cl atom kinetics alone and are attributed to additional Br atom reactions. A box modeling exercise suggested that the Cl and particularly Br atom concentrations required to explain the hydrocarbon behavior are also sufficient to destroy ozone.

Measurements of Photolyzable Halogen Compounds and Bromine Radicals During the Polar Sunrise Experiment 1997

As part of the Polar Sunrise Experiment (PSE) 1997, concentrations of halogen species thought to be involved in ground level Arctic ozone depletion were made at Alert, NWT, Canada (82.5°N, 62.3°W) during the months of March and April, 1997. Measurements were made of photolyzable chlorine (Cl2 and HOCl) and bromine (Br2 and HOBr) using the Photoactive Halogen Detector (PHD), and bromine radicals (BrOx) using a modified radical amplifier. During the sampling period between Julian Day 86 (March 27) and Day 102 (April 12), two ozone depletion episodes occurred, the most notable being on days 96-99, when ozone levels were below detectable limits (≈1 ppbv). Concentrations of BrOx above the 4 pptv detection limit were found for a significant part of the study, both during and outside of depletion events. The highest BrOx concentrations were observed at the end of the depletion event, when the concentration reached 15 pptv. We found substantial amounts of Br2 in the absence of O3, indicating that O3 is not a necessary requirement for production of Br2. There is also Br2 present when winds are from the south, implying local scale (e.g. from the snowpack) production. During the principal O3 depletion event, the HOBr concentration rose to ≈260 pptv, coincident with the BrOx maximum. This implies a steady state HO2 concentration of 6 pptv. During a partial O3 depletion event, we estimate that the flux of Br2 from the surface is about 10 times greater than that for Cl2.