ISSN:0148-0227    

DOI:10.1029/94JD01929

年代:1994

数据来源: WILEY

摘要:

A review of synoptic meteorological conditions in the Canadian Arctic was carried out in support of atmospheric chemistry studies during the 1992 Polar Sunrise Experiment. On the basis of the short‐term variability in concentrations of several constituents measured at Alert, Northwest Territories, Canada, distinctly different meteorological regimes were identified in the winter and spring. Variability was highest during the winter months, primarily due to the frequent occurrence of episodes of long‐range transport of primary pollutants. In the spring the short‐term variability in concentrations of many constituents was observed to decrease significantly. The long‐range transport events occurred only during the winter regime and accounted for over 40% of the observations made during the 1992 Polar Sunrise Experiment. The dominant transport pathway was across the Arctic Ocean from Eurasia. This pathway was established in the zone between large‐surface low‐pressure systems typically stretching from Iceland to the Kara Sea and a high‐pressure system over the Siberian/Beaufort Arctic. A secondary pathway was observed to bring pollutants with a southerly flow, from the direction of continental North America. The spring of 1992 had lower temperatures, lighter winds, and higher atmospheric pressures than in the previous four years. Four major O3depletion episodes were observed in April 1992. Synoptic and back‐trajectory analyses showed that these events could not be explained by long‐range transport. The recent (1–2 days) history of air parcels associated with these events appeared to be a more significant factor, and evidence of a marine influence w

ISSN:0148-0227    

DOI:10.1029/94JD02400

年代:1994

数据来源: WILEY

摘要:

In situ measurements of carbon dioxide, methane, black carbon, peroxyacetylnitrate, condensation nuclei, and radon were made from the Canadian Baseline Atmospheric Monitoring Observatory at Alert, Northwest Territories, Canada (82°28′N, 62°30′W′) during the “Polar Sunrise Experiment” (January 16 to April 20, 1992). The time series of methane, carbon dioxide, peroxyacetylnitrate, and black carbon were frequently highly correlated during January and February during well‐defined episodes lasting from 2 to 5 days. This is consistent with data from earlier years. Shortly after polar sunrise, the temporal variability in both trace gases and aerosols diminished. Using a definition of black carbon concentrations exceeding 100 ng m−3, 11 long‐range transport episodes were defined. Lagrangian 5‐day back trajectories along with the concentration data were classified into six geographical sectors to characterize the major episodes. The winter variability is related to synoptic meteorology, weak vertical mixing, and rapid air mass transport originating from Siberian and/or European source regions. Measurements of the radon daughter (222Rn) activity in the atmosphere were used to further explore the transport of continental material acro

ISSN:0148-0227    

DOI:10.1029/94JD01209

年代:1994

数据来源: WILEY

摘要:

Surface level ozone was measured continuously for the period January–April 1992 at two sites near Alert, Northwest Territories, Canada. Also, vertical profiles of ozone and meteorological parameters were measured at Alert with tethersondes for a selected period in April. Three ozone depletion events with ozone<0.5 ppb were recorded during April; tethersonde data were available for one of these events. Except for these ozone depletions the surface ozone concentration was lowest in January, in the range 25–30 ppb, and then progressively increased to a high in April, in the range of 40–45 ppb. Analysis of the present and some past ozone profile data from upper air sondes showed that ozone depletion at polar sunrise was associated with a neutral potential temperature profile within the boundary layer (i.e., low stability) capped by an elevated inversion at several hundred meters above the su

ISSN:0148-0227    

DOI:10.1029/94JD01312

年代:1994

数据来源: WILEY

摘要:

Grab samples for nonmethane hydrocarbons (NMHCs) were collected from three sites: daily at Alert, Northwest Territories (82.5° N, 62.3° W) from January 21 to April 19, daily at an ice floe 150 km north of Alert from April 9 to 25, and on an aerial survey conducted in April over the Arctic archipelago. Insitu measurements ofn‐butane andi‐pentane were also made hourly at Alert from April 2 to April 15. During the dark period (January to March), C2‐C6hydrocarbon concentrations correlated with those of methane. Concentrations declined gradually from January to April, consistent with removal by HO radicals. On the other hand, during low‐ozone periods in April an additional decrease in NMHC concentrations and change in distribution were observed. Concentration changes of alkanes were correlated to Cl atom reaction rate constants. Acetylene displayed a greater change in concentration than predicted from chlorine kinetics, possibly indicating additional removal by Br atoms. The Br atom concentration derived from the depletion of acetylene can account for the low‐ozone concentrations periodically observed at Alert. The estimated Cl atom concentration is too small to be a significant loss mechanism for ozone. Thus the data from Alert and the ice floe site provide evidence for Cl and Br atom chemistry during the ozone depletion episodes observed at po

ISSN:0148-0227    

DOI:10.1029/94JD01243

年代:1994

数据来源: WILEY

摘要:

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‐C7alkyl 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 −ONO2group(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 C3alkyl 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 C5isomers, was found to show substantial variations coinciding with the O3depletion 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 depleti

ISSN:0148-0227    

DOI:10.1029/94JD01309

年代:1994

数据来源: WILEY

摘要:

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 tropo

ISSN:0148-0227    

DOI:10.1029/94JD00227

年代:1994

数据来源: WILEY

摘要:

Atmospheric peroxides and formaldehyde were measured during the Polar Sunrise Experiment 1992 in Alert, Canada (82.5°N, 62.3°W). Two measurement periods, in the dark winter and in the sunlit spring, were chosen to investigate the effects of photochemistry. Continuous measurements were performed using diffusion scrubbers coupled to aqueous phase fluorometry. The concentration of total peroxides varied from below the detection limit (∼10 parts per trillion by volume (pptv)) to 40 pptv in the dark and 100 to 400 pptv in the sunlit period with large variations in the ratio between H2O2and organic peroxides. The CH2O concentrations measured in the dark were between 100 and 700 pptv and showed good correlation with a number of atmospheric constituents such as CH4, CO2, and Rn but anticorrelation to O3. A fraction of the observed CH2O concentrations is believed to be formed by nonphotochemical O3‐alkene chemistry. In the presence of sunlight the CH2O concentrations ranged between 30 to 600 pptv without correlation to CH4, CO2, or Rn. The maximum CH2O concentrations were associated with air, depleted in O3, coming from the Arctic Ocean. During the O3depletions, decreased peroxide concentrations were observed. The origin of the air mass was a very important factor during both periods in explaining the observed variabilities in CH2O and peroxide concentra

ISSN:0148-0227    

DOI:10.1029/94JD00547

年代:1994

数据来源: WILEY

摘要:

Bromine oxide (BrO) is proposed to be an important agent for tropospheric ozone depletion, as observed in the high Arctic during springtime. In this paper we report measurements of bromine oxide and ozone by Long Path Differential Optical Absorption Spectroscopy (LPDOAS), 8.6‐km light path), performed in April 1992 in Alert (82.3°N, 62.2°W). BrO mixing ratios were found between the detection limit of about 4 ppt to 17 ppt. Because of the frequently poor visibility conditions, especially during ozone depletion events, long‐signal integration times (sometimes more than 24 hours) were needed, and short‐time BrO‐peaks might have escaped detection. A pure in situ chemical mechanism based on BrO‐catalyzed ozone destruction cannot account for the observed complete depletion of ozone at the observed BrO mixing ratios. On the other hand, it can be argued that the maximum time for chemical ozone depletion (by any mechanism) may not be much longer than 1 day. A simple scenario involving a combination of advection, atmospheric dispersion, and BrO‐catalyzed chemical ozone destruction is described, which could explain the observ

ISSN:0148-0227    

DOI:10.1029/94JD01314

年代:1994

数据来源: WILEY

摘要:

Particle and gas phase inorganic bromine, total organic bromine, and several individual organic bromine species were measured in the troposphere during the Polar Sunrise Experiment at Alert, Northwest Territories, Canada, during January 18 to April 21, 1992. The measurements revealed the following: (1) Particle bromide increased gradually from about 10 ng (Br) m−3during the dark period to>20 ng(Br) m−3during the light period, with a marked peak of 120 ng(Br) m−3corresponding to a strong O3depletion event. (2) Inorganic gaseous bromine (InorgBr) was about 60 ng(Br) m−3during the dark period and relatively constant. A major peak, up to 280 ng(Br) m−3, before sunrise accompanied a similar peak in the total organic bromine. These episodes originated in the free troposphere over Greenland. After sunrise the peaks in InorgBr corresponded to O3depletion periods. InorgBr appeared to be the sum of HBr, HOBr, and Br2. (3) Total organic bromine was relatively constant before sunrise at 100 ng(Br) m−3but more variable afterward, up to 280 ng(Br) m−3. Individual species include CHBr3with levels of 7–60 ng(Br) m−3. CH2Br2, CH2ClBr, CHClBr2, and CHCl2Br levels were lower at 0.5–7.5 ng(Br) m−3. CHBr3was the largest contributor to total organic bromine of the five species, on average accounting for 23%, while the other four species amounted to less than 5% on average. CH3Br (not measured) should contribute 44% of total organic bromine assuming a concentration of 40 ng(Br) m−3(11 parts per trillion by volume). The remaining contribution was probably from ”missing„ species which were episodically dominant after sunrise with concentrations up to 240 ng(Br) m−3and may include some inorganic species. All the peaks in the organic bromines after sunrise corresponded to the O3depletion events. (4) CHBr3, CHClBr2, and CHCl2Br were significantly correlated. The ratio CHClBr2/CHBr3decreased linearly with increasing In(CHBr3), with a steeper decrease after sunrise than before. The decreases suggest different rates of destruction with CHBr3having a larger rate constant than CHClBr2. A similar relationship existed between the ratio CHCl2Br/CHClBr2and the In(CHClBr2), but the dark period slope was near zero, indicating a greater difference in rates in the tw

ISSN:0148-0227    

DOI:10.1029/93JD03343

年代:1994

数据来源: WILEY