Browsing by Author "Owen, R. Chris"
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- Late summer changes in burning conditions in the boreal regions and their implications for NO x and CO emissions from boreal firesPublication . Lapina, K.; Honrath, Richard; Owen, R. Chris; Val Martin, Maria; Hyer, E. J.; Fialho, PauloBuilding emission inventories for the fires in boreal regions remains a challenging task with significant uncertainties in the methods used. In this work, we assess the impact of seasonal trends in fuel consumption and flaming/smoldering ratios on emissions of species dominated by flaming combustion (e.g., NO x ) and species dominated by smoldering combustion (e.g., CO). This is accomplished using measurements of CO and NO y at the free tropospheric Pico Mountain observatory in the central North Atlantic during the active boreal fire seasons of 2004 and 2005. ΔNO y /ΔCO enhancement ratios in aged fire plumes had higher values in June-July (7.3 × 10−3 mol mol−1) relative to the values in August-September (2.8 × 10−3 mol mol−1), indicating that NO x /CO emission ratios declined significantly as the fire season progressed. This is consistent with our understanding that an increased amount of fuel is consumed via smoldering combustion during late summer, as deeper burning of the drying organic soil layer occurs. A major growth in fuel consumption per unit area is also expected, due to deeper burning. Emissions of CO and NO x from North American boreal fires were estimated using the Boreal Wildland Fire Emissions Model, and their long-range transport to the sampling site was modeled using FLEXPART. These simulations were generally consistent with the observations, but the modeled seasonal decline in the ΔNO y /ΔCO enhancement ratio was less than observed. Comparisons using alternative fire emission injection height scenarios suggest that plumes with the highest CO levels at the observatory were lofted well above the boundary layer, likely as a result of intense crown fires.
- Measurement of Aerosols and Trace Gases in the Free Troposphere at the Pico Mountain Observatory in the Azores.Publication . Kramer, Louisa; Mazzoleni, Claudio; Mazzoleni, Lynn R.; Fialho, Paulo; Helmig, Detlev; Olsen, Seth C.; Owen, R. Chris; Dziobak, Michael P.; Hueber, Jacques; Dzepina, Katja; Kumar, SumitHere, we present an overview of gas and aerosol data measured at the Pico Mountain Station. The primary objective of these measurements are to enhance our knowledge of anthropogenic and biomass burning emissions from North America and their relative impact on atmospheric composition and radiative forcing in the free troposphere of the North Atlantic.
- Molecular characterization of free tropospheric aerosol collected at the Pico Mountain Observatory : a case study with a long-range transported biomass burning plumePublication . Dzepina, Katja; Mazzoleni, Claudio; Fialho, Paulo; China, Swarup; Zhang, Bo; Owen, R. Chris; Helmig, Detlev; Hueber, Jacques; Kumar, Sumit; Perlinger, Judith A.; Kramer, Louisa; Dziobak, Michael P.; Ampadu, Marian T.; Olsen, Seth C.; Wuebbles, Donald J.; Mazzoleni, Lynn R.Free tropospheric aerosol was sampled at the Pico Mountain Observatory located at 2225 m above mean sea level on Pico Island of the Azores archipelago in the North Atlantic. The observatory is located ~ 3900 km east and downwind of North America, which enables studies of free tropospheric air transported over long distances. Aerosol samples collected on filters from June to October 2012 were analyzed to characterize organic carbon, elemental carbon, and inorganic ions. The average ambient concentration of aerosol was 0.9 ± 0.7 μg m−3. On average, organic aerosol components represent the largest mass fraction of the total measured aerosol (60 ± 51%), followed by sulfate (23 ± 28%), nitrate (13 ± 10%), chloride (2 ± 3%), and elemental carbon (2 ± 2%). Water-soluble organic matter (WSOM) extracted from two aerosol samples (9/24 and 9/25) collected consecutively during a pollution event were analyzed using ultrahigh-resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. Approximately 4000 molecular formulas were assigned to each of the mass spectra in the range of m/z 100–1000. The majority of the assigned molecular formulas had unsaturated structures with CHO and CHNO elemental compositions. FLEXPART retroplume analyses showed the sampled air masses were very aged (average plume age > 12 days). These aged aerosol WSOM compounds had an average O/C ratio of ~ 0.45, which is relatively low compared to O/C ratios of other aged aerosol. The increase in aerosol loading during the measurement period of 9/24 was linked to biomass burning emissions from North America by FLEXPART retroplume analysis and Moderate Resolution Imaging Spectroradiometer (MODIS) fire counts. This was confirmed with biomass burning markers detected in the WSOM and with the morphology and mixing state of particles as determined by scanning electron microscopy. The presence of markers characteristic of aqueous-phase reactions of phenolic species suggests that the aerosol collected at the Pico Mountain Observatory had undergone cloud processing before reaching the site. Finally, the air masses of 9/25 were more aged and influenced by marine emissions, as indicated by the presence of organosulfates and other species characteristic of marine aerosol. The change in the air masses for the two samples was corroborated by the changes in ethane, propane, and ozone, morphology of particles, as well as by the FLEXPART retroplume simulations. This paper presents the first detailed molecular characterization of free tropospheric aged aerosol intercepted at a lower free troposphere remote location and provides evidence of low oxygenation after long-range transport. We hypothesize this is a result of the selective removal of highly aged and polar species during long-range transport, because the aerosol underwent a combination of atmospheric processes during transport facilitating aqueous-phase removal (e.g., clouds processing) and fragmentation (e.g., photolysis) of components.
- Molecular characterization of free tropospheric aerosol collected at the Pico Mountain Observatory : a case study with long range transported biomass burning plumesPublication . Dzepina, Katja; Mazzoleni, Claudio; Fialho, Paulo; China, Swarup; Zhang, Bo; Owen, R. Chris; Helmig, Detlev; Hueber, Jacques; Kumar, Sumit; Perlinger, Judith A.; Kramer, Louisa; Dziobak, Michael P.; Ampadu, Marian T.; Olsen, Seth C.; Wuebbles, Donald J.; Mazzoleni, Lynn R.Free tropospheric aerosol was sampled at the Pico Mountain Observatory located at 2225 m above mean sea level on Pico Island of the Azores archipelago in the North Atlantic. The observatory is located ~ 3900 km east and downwind of North America, which enables studies of free tropospheric air transported over long distances. Aerosol samples collected on filters from June to October 2012 were analyzed to characterize organic carbon, elemental carbon, and inorganic ions. The average ambient concentration of aerosol was 0.9 ± 0.7 μg m−3. On average, organic aerosol components represent the largest mass fraction of the total measured aerosol (60 ± 51%), followed by sulfate (23 ± 28%), nitrate (13 ± 10%), chloride (2 ± 3%), and elemental carbon (2 ± 2%). Water-soluble organic matter (WSOM) extracted from two aerosol samples (9/24 and 9/25) collected consecutively during a pollution event were analyzed using ultrahigh-resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. Approximately 4000 molecular formulas were assigned to each of the mass spectra in the range of m/z 100–1000. The majority of the assigned molecular formulas had unsaturated structures with CHO and CHNO elemental compositions. FLEXPART retroplume analyses showed the sampled air masses were very aged (average plume age > 12 days). These aged aerosol WSOM compounds had an average O/C ratio of ~ 0.45, which is relatively low compared to O/C ratios of other aged aerosol. The increase in aerosol loading during the measurement period of 9/24 was linked to biomass burning emissions from North America by FLEXPART retroplume analysis and Moderate Resolution Imaging Spectroradiometer (MODIS) fire counts. This was confirmed with biomass burning markers detected in the WSOM and with the morphology and mixing state of particles as determined by scanning electron microscopy. The presence of markers characteristic of aqueous-phase reactions of phenolic species suggests that the aerosol collected at the Pico Mountain Observatory had undergone cloud processing before reaching the site. Finally, the air masses of 9/25 were more aged and influenced by marine emissions, as indicated by the presence of organosulfates and other species characteristic of marine aerosol. The change in the air masses for the two samples was corroborated by the changes in ethane, propane, and ozone, morphology of particles, as well as by the FLEXPART retroplume simulations. This paper presents the first detailed molecular characterization of free tropospheric aged aerosol intercepted at a lower free troposphere remote location and provides evidence of low oxygenation after long-range transport. We hypothesize this is a result of the selective removal of highly aged and polar species during long-range transport, because the aerosol underwent a combination of atmospheric processes during transport facilitating aqueous-phase removal (e.g., clouds processing) and fragmentation (e.g., photolysis) of components.
- Regional and hemispheric impacts of anthropogenic and biomass burning emissions on summertime CO and O3 in the North Atlantic lower free tropospherePublication . Honrath, Richard; Owen, R. Chris; Val Martin, Maria; Reid, J. S.; Lapina, K.; Fialho, Paulo; Dziobak, Michael P.; Kleissl, J.; Westphal, D. L.We report summertime measurements of CO and O3 obtained during 2001–2003 at the PICO-NARE mountaintop station in the Azores. Frequent events of elevated CO mixing ratios were observed. On the basis of backward trajectories arriving in the free troposphere and global simulations of biomass burning plumes, we attribute nearly all these events to North American pollution outflow and long-range transport of biomass burning emissions. There was a high degree of interannual variability in CO levels: median [CO] ranged from 65 ppbv in 2001 to 104 ppbv in 2003. The highest concentrations were associated with transport of Siberian fire emissions during summer 2003, when Siberian fire activity was unusually high. Ozone mixing ratios also increased (by up to ∼30 ppbv) during the fire events. These findings demonstrate the significant hemispheric scale impact that biomass burning events have on background CO and O3 levels. O3 enhancements of similar magnitude were also observed in North American pollution outflow. O3 and CO were correlated during North American outflow events, with a slope averaging 1.0 (d[O3]/d[CO], ppbv/ppbv) when no fire impact was present. This slope is more than 80% larger than early 1990s observations made in the eastern United States and nearshore outflow region, even after accounting for declining U.S. CO emissions and for CO loss during transport to the Azores, and is not consistent with simple dilution of U.S. outflow with marine background air. We conclude that a significantly larger amount of O3 production occurred in the air sampled during this study, and we suggest several potential reasons for this, each of which could imply potentially significant shortcomings in current estimates of the hemispheric impact of North American emissions on tropospheric ozone and should be evaluated in future studies.
- Significant enhancements of nitrogen oxides, black carbon, and ozone in the North Atlantic lower free troposphere resulting from North American boreal wildfiresPublication . Val Martin, Maria; Honrath, Richard; Owen, R. Chris; Pfister, Gabriele; Fialho, Paulo; Barata, FilipeExtensive wildfires burned in northern North America during summer 2004, releasing large amounts of trace gases and aerosols into the atmosphere. Emissions from these wildfires frequently impacted the PICO-NARE station, a mountaintop site situated 6–15 days downwind from the fires in the Azores Islands. To assess the impacts of the boreal wildfire emissions on the levels of aerosol black carbon (BC), nitrogen oxides and O3 downwind from North America, we analyzed measurements of CO, BC, total reactive nitrogen oxides (NO y ), NO x (NO + NO2) and O3 made from June to September 2004 in combination with MOZART chemical transport model simulations. Long-range transport of boreal wildfire emissions resulted in large enhancements of CO, BC, NO y and NO x , with levels up to 250 ppbv, 665 ng mˉ³, 1100 pptv and 135 pptv, respectively. Enhancement ratios relative to CO were variable in the plumes sampled, most likely because of variations in wildfire emissions and removal processes during transport. Analyses of ΔBC/ΔCO, ΔNO y /ΔCO and ΔNO x /ΔCO ratios indicate that NO y and BC were on average efficiently exported in these plumes and suggest that decomposition of PAN to NO x was a significant source of NO x . High levels of NO x suggest continuing formation of O3 in these well-aged plumes. O3 levels were also significantly enhanced in the plumes, reaching up to 75 ppbv. Analysis of ΔO3/ΔCO ratios showed distinct behaviors of O3 in the plumes, which varied from significant to lower O3 production. We identify several potential reasons for the complex effects of boreal wildfire emissions on O3 and conclude that this behavior needs to be explored further in the future. These observations demonstrate that boreal wildfire emissions significantly contributed to the NO x and O3 budgets in the central North Atlantic lower free troposphere during summer 2004 and imply large-scale impacts on direct radiative forcing of the atmosphere and on tropospheric NO x and O3.
- Ten Years of Black Carbon Measurements in the North Atlantic at the Pico Mountain Observatory, Azores (2225m asl).Publication . Kumar, Sumit; Fialho, Paulo; Mazzoleni, Lynn R.; Olsen, Seth C.; Owen, R. Chris; Helmig, Detlev; Hueber, Jacques; Dziobak, Michael P.; Kramer, Louisa; Mazzoleni, ClaudioThe Pico Mountain Observatory is located in the summit caldera of the Pico mountain, an inactive volcano on the Pico Island in the Azores, Portugal (38.47°N, 28.40°W, Altitude 2225m asl). The Azores are often impacted by polluted outflows from the North American continent and local sources have been shown to have a negligible influence at the observatory. The value of the station stems from the fact that this is the only permanent mountaintop monitoring station in the North Atlantic that is typically located above the marine boundary layer (average MBL heights are below 1200 m and rarely exceed 1300 m) and often receives air characteristic of the lower free troposphere. Measurements of black carbon (BC) mass have been carried out at the station since 2001, mostly in the summer seasons. Here we discuss the BC decadal dataset (2001-2011) collected at the site by using a seven-wavelength AE31 Magee Aethalometer. Measured BC mass and computed Angstrom exponent (AE) values were analysed to study seasonal and diurnal variations. There was a large day-to-day variability in the BC values due to varied meteorological conditions that resulted in different diurnal patterns for different months. The daily mean BC at this location ranged between 0 and ~430 ngm-3, with the most frequently occurring value in the range 0-100 ngm-3. The overall mean for the 10 year period is ~24 ngm-3, with a coefficient of variation of 150%. The BC values exhibited a consistent annual trend being low in winter months and high in summer months, barring year to year variations. To differentiate between BC and other absorbing particles, we analyzed the wavelength dependence of aerosol absorption coefficient and determined a best-fit exponent i.e., the Ångström exponent, for the whole dataset. Visible Ångström exponent (AE: 470-520-590-660 nm) values ranged between 0 and 3.5, with most frequently occurring values in the range 0.85 to 1.25. By making use of the aethalometer light attenuation measurements at different wavelengths and Hysplit back trajectories, we divided the data into two categories. One for periods characterized by AE values close to 1; these periods are typically correlated with back trajectories originating from Canada, North America or northern Europe, indicating the dominance of BC on the light attenuation. Another characterized by AE values substantially different from 1; these periods correlated with back trajectories originating from dust-prone regions (e.g., the Sahara desert).The above measurements, with the aid of ancillary satellite and ground-based measurements will be employed in estimating the radiaitve effects of BC in the North Atlantic.