Measurement of Free Tropospheric Aerosols in the North Atlantic at the Pico Mountain Observatory.

AAAR 31st Annual Conference. Minneapolis, Minnesota, October 8-12, 2012.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 (38º28'15''N; 28º24’'14''W). 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

Regional and hemispheric impacts of anthropogenic and biomass burning emissions on summertime CO and O3 in the North Atlantic lower free troposphere

Copyright © 2004 American Geophysical Union. All Rights Reserved.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

Ten Years of Black Carbon Measurements in the North Atlantic at the Pico Mountain Observatory, Azores (2225m asl).

45th annual Fall Meeting, AGU. San Francisco, California, 3-7 December.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

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

Measurement of Aerosols and Trace Gases in the Free Troposphere at the Pico Mountain Observatory in the Azores.

European Geosciences Union (EGU), General Assembly. Viena, Austria, 07 - 12 April 2013.Here, 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

Free Tropospheric Aerosol Measurements at the Pico Mountain Observatory, Azores (2225m asl).

AAAR 31st Annual Conference. Minneapolis, Minnesota, October 8-12, 2012.In this poster we discuss a limited subset of the aerosol measurements performed at the Pico Mountain Observatory. The Black Carbon (BC) mass shows a clear seasonal pattern over a ten-years period. The 2012 scattering measurements show highly variable signals with events with high scattering and periods of very low aerosol loading. Dust events are clearly captured by the aethalometer, as well the nephelometer Ångström exponents. Particles have various shapes, and mixing states, and soot particles typically are very compacted

Aerosol Measurements in the Free Troposphere at the North Atlantic Pico Mountain Observatory in the Azores.

3th Atmospheric Science Research (ASR), Science Team Meeting. Arlington, Virginia, March 12-16, 2012.Pico is a small island (447 km2) in the archipelago of the Azores, Portugal, in the North Atlantic Ocean. The island has a very steep inactive volcano. An atmospheric monitoring station (Pico Mountain Observatory) was established close to the summit of the volcano by the late Dr. Richard Honrath and colleagues in 2001. The station, far from persistent local sources, is located near the northern cliff of the summit caldera at an altitude of 2225 meters. The station altitude is typically well above the boundary layer during summertime, when average marine boundary-layer heights are below 1200 meters and rarely exceed 1300 meters. Air masses reaching the station are often transported from North America and seldom from Europe or North Africa. The station’s uniqueness and significance lie in its location that allows study of the transport and evolution of gases and aerosols from North America in the free troposphere. Until recently, the focus was on the measurement and analysis of trace gases (ozone, carbon monoxide, non-methane hydrocarbons, nitrogen oxides) and light-absorbing aerosol (black carbon and iron oxide). Aerosol light attenuation has been measured at the site since 2001 using a seven-wavelengths aethalometer. An optical particle sizer was installed at the site in 2010 and has been running in parallel to the aethalometer for two seasons. A three-wavelength nephelometer, to measure the aerosol total- and back-scattering, and aerosol samplers for morphological and chemical analysis will be installed at the site in 2012. Our goal is to enhance the observatory monitoring capabilities for aerosol research. The objectives of this new research program are to: (a) assess background as well as specific event tropospheric aerosol properties, (b) compare aerosol and gases measurements with model outputs, and (c) use the data collected to provide satellite validation. This research is anticipated to enhance our understanding of the interactions between tropospheric aerosols, clouds, and climate by allowing, for example, the analysis of North American outflows and seasonal changes, the assessment of different source regions, the estimation of aerosol radiative forcing above marine clouds and in clear sky, and the study of the relative contribution of anthropogenic versus biomass burning emissions. In this poster we present a preliminary analysis of the black carbon and aerosol size data in conjunction with retroplume model analysis

Properties of Aerosol in the North Atlantic Free Troposphere at the Pico Mountain Observatory, Azores.

4th Atmospheric System Research (ASR), Science Team Meeting. Potomac, Maryland, March 18-21, 2013.The Pico Mountain Observatory is located at an altitude of 2225 meters above sea level in the summit caldera of the Pico volcano in the Azores, Portugal (38.47°N, 28.40°W). The scientific value of the station stems from the fact that this is the only permanent free-tropospheric monitoring station in the central North Atlantic, with negligible influence from local sources and that frequently samples air from the North American continent. Thus, it is an ideal site for studying long-range transported pollution. The station started operating in 2001 with a focus on gaseous species (e.g., ozone, carbon monoxide, nitrogen oxides, and non-methane hydrocarbons) and aerosol particles that absorb light (black carbon [BC] and aerosol dust). The absorbing aerosol mass concentrations, in units of equivalent black carbon mass concentrations, have been monitored using a seven-wavelength aethalometer (Magee scientific model AE31). Ancillary measurements at the station include meteorological parameters such as temperature, relative humidity, pressure, wind direction, and speed. Due to the harsh environmental conditions at the site, most measurements have been performed during the summer seasons. In the summer of 2012, new aerosol instrumentation and samplers were installed at the station. The new equipment includes a three-wavelength nephelometer (Ecotech model Aurora 3000) that measure aerosol scattering and backscattering fraction, a set of four high-volume samplers for the collection and chemical analysis of aerosol, a sequential sampler to collect aerosols on membranes and grids, and an optical particle counter. Membranes and grids are analysed offline with scanning and transmission electron microscopy to study morphological properties and elemental composition of the aged aerosols. In this poster we will discuss some of the analysis of the decadal BC mass concentration data, as well as some analysis of the new aerosol data with a focus on aerosol optical properties and morphology. Analysis of these properties is important for a better understanding of aerosol’s life cycle and ageing during their transport over the Atlantic, with implications on aerosol radiative properties and climate science

Decomposition Rates, Synthesis, and Spectral Properties of a Series of Alkyl Hyponitrites

A number of trans-alkyl hyponitrites (RON=NOR) weee synthesized and characterized. At 66.1 - 0.1 °C in isooctane and with millimolar to micromolar concentrations first-order kinetics were observed with half-lives (min) of 12.8 - 0.2 (CH3), 32.3 - 1.1 (2-C3H7), 15.0 - 0.3 (cyclohexyl), 25.2 - 1.2 (tert-butyl), 18.3 - 0.3 (tert-pentyl), 3.0 - 0.1 (benzyl), 11.2 - 0.5 (2-phenylethyl), and 5.5 - 0.3 (1-phenylethyl). The rate constants were concentration independent and showed little change with changes in solvent polarity or viscosity. Ultraviolet, magnetic resonance, infrared, and mass spectra for the new hyponitrites are reported. Most of the hyponitrites were highly crystalline solids that could be stored for long periods without change below 0 °C. © 1983, American Chemical Society. All rights reserved

Morphology and mixing state of aged soot particles at a remote marine free troposphere site

The radiative properties of soot particles depend on their morphology and mixing state, but their evolution during transport is still elusive. Here we report observations from an electron microscopy analysis of individual particles transported in the free troposphere over long distances to the remote Pico Mountain Observatory in the Azores in the North Atlantic. Approximately 70% of the soot particles were highly compact and of those 26% were thinly coated. Discrete dipole approximation simulations indicate that this compaction results in an increase in soot single scattering albedo by a factor of <= 2.17. The top of the atmosphere direct radiative forcing is typically smaller for highly compact than mass-equivalent lacy soot. The forcing estimated using Mie theory is within 12% of the forcing estimated using the discrete dipole approximation for a high surface albedo, implying that Mie calculations may provide a reasonable approximation for compact soot above remote marine clouds