Elton Chan

Influence of transport and ocean ice extent on biogenic aerosol sulfur in the Arctic atmosphere

The recent decline in sea ice cover in the Arctic Ocean could affect the regional radiative forcing via changes in sea ice-atmosphere exchange of dimethyl sulfide (DMS) and biogenic aerosols formed from its atmospheric oxidation, such as methanesulfonic acid (MSA). This study examines relationships between changes in total sea ice extent north of 70 degrees N and atmospheric MSA measurement at Alert, Nunavut, during 1980-2009; at Barrow, Alaska, during 1997-2008; and at Ny-Alesund, Svalbard, for 1991-2004. During the 1980-1989 and 1990-1997 periods, summer (July-August) and June MSA concentrations at Alert decreased. In general, MSA concentrations increased at all locations since 2000 with respect to 1990 values, specifically during June and summer at Alert and in summer at Barrow and Ny-Alesund. Our results show variability in MSA at all sites is related to changes in the source strengths of DMS, possibly linked to changes in sea ice extent as well as to changes in atmospheric transport patterns. Since 2000, a late spring increase in atmospheric MSA at the three sites coincides with the northward migration of the marginal ice edge zone where high DMS emissions from ocean to atmosphere have previously been reported. Significant negative correlations are found between sea ice extent and MSA concentrations at the three sites during the spring and June. These results suggest that a decrease in seasonal ice cover influencing other mechanisms of DMS production could lead to higher atmospheric MSA concentrations.

Regional ground‐level ozone trends in the context of meteorological influences across Canada and the eastern United States from 1997 to 2006

[1] Meteorologically adjusted trends for different ozone averaging metrics (including daily maximum 1 h, daily maximum 8 h average, daily average, daytime average, nighttime average, daily minimum 8 h average, and monthly 5th percentile of ozone mixing ratios) were investigated in different regions of Canada and the United States over the time period 1997-2006. The spatiotemporal variability of the May-September daily ozone mixing ratios from 97 nonurban ozone measurement sites in Canada and the United States was examined to establish regions of common variability using rotated principal component analysis (R-PCA). This was followed by modeling multiple sites within the PCA-derived regions for all months using generalized linear mixed models. Most regions in southeastern Canada and the eastern United States showed statistically significant decreasing trends in the daily maximum 8 h average ranging from 0.53 ± 0.2 to 2.7 ± 0.86%/a, whereas significant increasing trends of 0.44 ± 0.37%/a and 0.98 ± 0.76%/a were found in Atlantic and Pacific Canada, respectively. In southeastern Canada and the eastern United States, the rates of decrease of the meteorologically adjusted regional trends associated with low ozone levels were slower than those of high levels. However, the rates of increase in the Atlantic and Pacific coastal regions associated with low levels were faster than those of high levels. These results are consistent with decreasing NO x and nonmethane hydrocarbon emissions in southeastern Canada and the eastern United States starting in the early 2000s and a hypothesized widespread increase due to the rising hemispheric background ozone.

Regional non-CO2 greenhouse gas fluxes inferred from atmospheric measurements in Ontario, Canada

Independent verification of bottom-up greenhouse gas (GHG) emission inventories is crucial for a reliable reporting of Kyoto gases to the United Nations Framework Convention on Climate Change. Here, we use a pseudo-data experiment to test if our improved version of the well-known Radon tracer method (RTM) is able to quantitatively retrieve regional GHG fluxes. Using in-situ observations in Egbert, Canada, from 2006 to 2009 for the RTM, we derive night-time fluxes of CH4 and N2O in southern Ontario. The N2O fluxes found have a inter-quartile range of 7.6–31.2 μgN2O/(m2h) with an overall mean of 24.4 ± 5.6 μgN2O/(m2h). Comparison with the EDGAR4.1 inventory revealed an underestimation by a factor of 1.7 ± 0.4 in the inventory, which is explainable by missing natural sources and a missing seasonal cycle in the inventory. Our RTM-based fluxes of CH4 with a inter-quartiles range of 0.19–0.49 mgCH4/(m2h) and a mean of 0.36 ± 0.08 mgCH4/(m2h) lie significantly below the inventory-based estimates of 0.79 ± 0.06 mgCH4/(m2h). Using a Stochastic Time-Inverted Lagrangian Transport (STILT) model this difference can be attributed to an overestimation of CH4 emissions in a specific region, the highly urbanized Greater Toronto Area. This study displays how the application of the RTM in future monitoring networks could help to assess high-resolution emission inventories.