Arsineh Hecobian

Patterns of CO2and radiocarbon across high northern latitudes during International Polar Year 2008

High-resolution in situ CO_2 measurements were conducted aboard the NASA DC-8 aircraft during the ARCTAS/POLARCAT field campaign, a component of the wider 2007–2008 International Polar Year activities. Data were recorded during large-scale surveys spanning the North American sub‐Arctic to the North Pole from 0.04 to 12 km altitude in spring and summer of 2008. Influences on the observed CO_2 concentrations were investigated using coincident CO, black carbon, CH_3CN, HCN, O_3, C_2Cl_4, and Δ^(14)CO_2 data, and the FLEXPART model. In spring, the CO_2 spatial distribution from 55°N to 90°N was largely determined by the long-range transport of air masses laden with Asian anthropogenic pollution intermingled with Eurasian fire emissions evidenced by the greater variability in the mid-to-upper troposphere. At the receptor site, the enhancement ratios of CO_2 to CO in pollution plumes ranged from 27 to 80 ppmv ppmv^(−1) with the highest anthropogenic content registered in plumes sampled poleward of 80°N. In summer, the CO_2 signal largely reflected emissions from lightning-ignited wildfires within the boreal forests of northern Saskatchewan juxtaposed with uptake by the terrestrial biosphere. Measurements within fresh fire plumes yielded CO_2 to CO emission ratios of 4 to 16 ppmv ppmv^(−1) and a mean CO_2 emission factor of 1698 ± 280 g kg^(−1) dry matter. From the ^(14)C in CO_2 content of 48 whole air samples, mean spring (46.6 ± 4.4‰) and summer (51.5 ± 5‰) Δ^(14)CO_2 values indicate a 5‰ seasonal difference. Although the northern midlatitudes were identified as the emissions source regions for the majority of the spring samples, depleted Δ^(14)CO_2 values were observed in <1% of the data set. Rather, ARCTAS Δ^(14)CO_2 observations (54%) revealed predominately a pattern of positive disequilibrium (1–7‰) with respect to background regardless of season owing to both heterotrophic respiration and fire-induced combustion of biomass. Anomalously enriched Δ^(14)CO_2 values (101–262‰) measured in emissions from Lake Athabasca and Eurasian fires speak to biomass burning as an increasingly important contributor to the mass excess in Δ^(14)CO_2 observations in a warming Arctic, representing an additional source of uncertainty in the quantification of fossil fuel CO_2.

Open-path cavity ring-down spectroscopy for trace gas measurements in ambient air

The present work used a near-infrared methane cavity ring-down spectroscopy (CRDS) sensor to examine performance and limitations of open-path CRDS for atmospheric measurements. A simple purge-enclosure was developed to maintain high mirror reflectivity and allowed >100 hours of operation with mirror reflectivity above 0.99996. We characterized effects of aerosols on ring-down decay signals and found the dominant effect to be fluctuations by large super-micron particles. Simple software filtering approaches were developed to combat these fluctuations allowing noise-equivalent sensitivity of ~6x10-10 cm-1HJ Hz-1/2 within a factor of ~3 of closed-path systems (based on stability of the absorption baseline). Sensor measurements were validated against known methane concentrations in a closed-path configuration, while open-path validation was performed by side-by-side comparison with a commercial closed-path system.

Chemical composition and emissions factors for cookstove startup (ignition) materials

Air pollution from cookstoves creates a substantial human and environmental health burden. A disproportionate fraction of emissions can occur during stove ignition (startup) compared to main cooking, yet startup material emissions are poorly quantified. Laboratory tests were conducted to measure emissions from startups using kerosene, plastic bags, newspaper, fabric, food packaging, rubber tire tubes, kindling, footwear, and wood shims. Measured pollutants included: fine particulate matter mass (PM2.5), PM2.5 elemental and organic carbon, methane, carbon monoxide, carbon dioxide, benzene, and formaldehyde. Results demonstrate substantial variability in the measured emissions across materials on a per-startup basis. For example, kerosene emitted 496 mg PM2.5 and 999 mg CO per startup, whereas plastic bags emitted 2 mg PM2.5 and 30 mg CO. When considering emissions on a per-mass basis, the ordering of materials from highest-to-lowest emissions changes, emphasizing the importance of establishing how much material is needed to start a stove. The proportional contribution of startups to overall emissions varies depending on startup material type, stove type, and cooking event length; however, results demonstrate that startup materials can contribute substantially to a cookstoves emissions. Startup material choice is especially important for cleaner stove-fuel combinations where the marginal benefits of reduced emissions are potentially greater.