Release of NO(x) from sunlight-irradiated midlatitude snow

Photochemical production and release of gas-phase NO(x) (NO + NO2) from the natural snowpack at a remote site in northern Michigan were investigated during the Snow Nitrogen and Oxidants in Winter study in January 1999. Snow was collected in an open 34 L chamber, which was then sealed with a transparent Teflon cover and used as an outdoor flow and reaction chamber. Significant increases in NO(x) mixing ratio were observed in synthetic and ambient air pulled through the sunlit chamber. [NO(x)] enhancements were correlated to ultraviolet sunlight intensity, reaching ~300 pptv under partially overcast midday, mid-winter conditions. These findings are consistent with NO(x) production from photolysis of snowpack NO3 -; the observed NO(x) release implies production of significant amounts of OH within the snow. Snowpack NO3 - photolysis may therefore significantly alter boundary layer levels of both NO(x) and oxidized compounds over wide regions of the atmosphere

A permanent free tropospheric observatory at Pico summit in the Azores Islands? Past measurements (2001–2005) and future plans.

AGU Fall Meeting. San Francisco, California, 5-9 December 2005.Pico mountain in the Azores Islands provides a base for continuous, free tropospheric measurements that is unique in the central North Atlantic region. The PICO-NARE station was installed there in 2001 as a temporary observatory. However, the location proved ideal for studies of aged emissions from anthropogenic (N. American) and boreal fire (N. American and Russian) emissions, as well as for less frequent interception of European and African plumes. As a result, station operation was continued through summer 2005, and we are planning for continuing operation and conversion into a permanent Portuguese GAW station in the future. This poster will provide an overview of the station, the measurements made there, typical transport pathways to the station and interannual variability in transport, and an overview of the full suite of multi-season observations and key findings from measurements to date. In addition, data availability and near-term and long-term plans for the station's future will be discussed

2,2-Di-(4-tert-octylphenyl)-1-picrylhydrazyl as an alkane-soluble standard for electron paramagnetic resonance studies

The title compound a waxy DPPH , was synthesized in three steps from p,p′-di-tert-octyldiphenylamine. The new radical showed spectral properties that were nearly identical to those of 2,2-diphenyl-1-picrylhydrazyl (DPPH), and it easily dissolved in all organic solvents tested except fluoroblube and ethylene glycol. The radical was monomeric at -95°C in isooctane at a concentration of 0.4. mM. © 1982

Thermal decomposition of sodium trans-hyponitrite

Samples of amorphous sodium trans-hyponitrite (Na2N2O2), heated with a continuous rise in temperature in the absence of oxygen, decompose suddenly between 360 and 390°C. The decomposition products are Na2O and N2O, along with secondary reaction products derived from N2O. When Na2N2O2 is heated in an O2-containing atmosphere, the decomposition temperatures are lowered due to the slow oxidation of N2O22- to NO2- and of NO2- to NO3-, which accumulate and increase the decomposition rate. At P(O2) = 754 Torr, the isothermal induction period for Na2N2O2 between 275 and 315°C is given approximately by log (t(min)) = -14.8 ± 0.3 + (41090 ± 600 cal)/2.3RT. At 298 ± 2°C, the induction period of Na2N2O2 depends inversely on oxygen pressure (100-745 Torr), with a purified sample showing t(min) = 4.83 + 4902/P°(O2, Torr). © 1989 American Chemical Society

Occurrence of upslope flows at the Pico mountaintop observatory: A case study of orographic flows on a small, volcanic island

Upslope flows caused by mechanical forcing in strong synoptic winds or by buoyant forcing driven by solar heating under weak synoptic winds can influence the air composition at mountaintop observatories. Using meteorological and trace gas measurements at the PICO-NARE observatory on Pico mountain (Azores Islands, North Atlantic Ocean), the frequency and impact of such orographic flows on a small, volcanic, subtropical island was examined. To determine the origin of mechanically lifted air, upstream kinetic energy was balanced against potential energy gained during uplift (Sheppard\u27s model). Mechanically forced upslope flow is most important during October through April, when the calculated probability of observing marine boundary layer (MBL) air at the observatory near the summit ranges from 35 to 60% per month. In contrast, lower synoptic wind speeds and a more stable lower free troposphere during May-September result in a reduced frequency of MBL impacts ( \u3c 20%). Buoyant upslope flows (BUF) were quantified through meteorological measurements on the mountain slope in summer 2004. Diurnal cycles of wind direction on the mountain slope consistent with daytime upslope and nighttime downslope flow were found on 24% of the days during late June, July, and August 2004. Buoyant forcing can also occur in the presence of moderate synoptic winds, resulting in enhancement of the mechanically forced upslope flow on the windward side of the mountain. Such conditions were found on 15% of the summer days in 2004. However, on BUF days the specific humidity at the mountaintop was significantly smaller than on the slope, indicating turbulent mixing during ascent or vertical decoupling of air masses. Impacts of BUF or a mixture of buoyant and mechanical upslope flow on O \u3c inf\u3e 3 or nitrogen oxides mixing ratios at the mountaintop station were rare or extremely small, and no significant diurnal. cycle of O \u3c inf\u3e 3 (expected if daytime BUF of MBL air occurred regularly) was present. Midday increases in isoprene concentrations, a nonmethane hydrocarbon (NMHC) expected to be emitted from vegetation more than 700 in below the PICO-NARE station, were found on 54% of the days during May-August 2005. No corresponding increase in n-butane (used for heating and cooking at sea level residences) was detected, suggesting that the air did not originate from as low as sea level. These results indicate that the latitude, size, and topography of Pico island combine to prevent frequent transport of MBL air to the PICO-NARE station in the summer. Copyright 2007 by the American Geophysical Union

Regional and hemispheric impacts of anthropogenic and biomass burning emissions on summertime CO and O \u3c inf\u3e 3 in the North Atlantic lower free troposphere

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. Copyright 2004 by the American Geophysical Union

Optical properties of aged free tropospheric aerosol over the Northern Atlantic: Analysis of 2012-2014 data

The Azores are a volcanic archipelago located 1500km west of Lisbon, Portugal in the North Atlantic Ocean. A 2351 meter dormant volcano lies on the 447 km2island of Pico with a population of around 15,000. Its location and orography are such that the summit typically lies above the well mixed marine boundary layer. A station was established in the caldera of the volcano at 2225 m by the late Dr. Richard Honrath in collaboration with the University of the Azores and began collecting data in 2001. A seven-wavelength aethalometer was employed to measure the black carbon equivalent mass concentration in the free troposphere since then. In 2012 a three wavelength nephelometer was added to measure total light scattering and back scattering due to aerosol. In 2013 an optical particle counter was added. Aerosol, including black carbon, play an important role in atmospheric processes for a number of reasons including different radiative forcing effects, acting as a cloud condensation and ice nuclei and changing surface albedo of snow. We present the wavelength-dependent aerosol optical properties measured during the 2012, 2013 and 2014 sampling seasons along with particle count data when available. Several events with high aerosol concentrations are investigated in detail

Measurement of free tropospheric aerosols in the North Atlantic at the Pico Mountain Observatory

The Pico Mountain Observatory is located at 2225 m amsl on an inactive volcano at Pico Island in the Azores archipelago in the North Atlantic ~3900 km east and downwind of North America (38º28\u2715\u27\u27N; 28º24’\u2714\u27\u27W). The unique location of the Observatory enables sampling of free tropospheric air transported over long, intercontinental distances and is rarely affected by local emissions. The Observatory is affected mainly by North American outflow after its trans-Atlantic transport. Therefore, its location is ideal for observations of long-range transported pollutants emitted from anthropogenic and biogenic continental sources. The composition of continental pollution outflow is altered during transport by mixing, chemical reactions, phase changes, and removal processes. Thus, the properties of aerosol and trace gases in downwind regions are impacted by the outflow of pollutants, their chemical transformation, and sinks. In previous work, the sampled air-mass measurements (including CO, O3, NOx, NOy, NMHC, black carbon and aerosol optical size) and the simulations of their dispersion indicated outflow of North American tropospheric ozone and its precursors. Although the measurements have been crucial in explaining the evolution of North American gaseous pollution, little is known regarding the nature of the aged aerosol. New work is currently underway at the Observatory to provide chemical characterization of the intercepted free tropospheric aerosols. Here, we show the preliminary results of the free tropospheric aerosol composition and its physical properties. Samples were collected using high-volume filter samplers with quartz filters and analyzed for organic and elemental carbon (OC and EC, respectively). We compare the observed OC and EC values to the collocated measurements of gas- and particle-phase species, meteorological parameters and to the values found in current literature. We highlight the future work in which we will select filter samples based on the arrival of highly polluted air masses from anthropological or biomass burning emissions for further detailed analysis

Ten years of black carbon measurements in the North Atlantic at the Pico Mountain Observatory, Azores (2225m asl)

The 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.ico Mountain Observator