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

Ice cloud formation potential by free tropospheric particles from long-range transport over the Northern Atlantic Ocean

Long-range transported free tropospheric particles can play a significant role on heterogeneous ice nucleation. Using optical and electron microscopy we examine the physicochemical characteristics of ice nucleating particles (INPs). Particles were collected on substrates from the free troposphere at the remote Pico Mountain Observatory in the Azores Islands, after long-range transport and aging over the Atlantic Ocean. We investigate four specific events to study the ice formation potential by the collected particles with different ages and transport patterns. We use single-particle analysis, as well as bulk analysis to characterize particle populations. Both analyses show substantial differences in particle composition between samples from the four events; in addition, single-particle microscopy analysis indicates that most particles are coated by organic material. The identified INPs contained mixtures of dust, aged sea salt and soot, and organic material acquired either at the source or during transport. The temperature and relative humidity (RH) at which ice formed, varied only by 5% between samples, despite differences in particle composition, sources, and transport patterns. We hypothesize that this small variation in the onset RH may be due to the coating material on the particles. This study underscores and motivates the need to further investigate how long-range transported and atmospherically aged free tropospheric particles impact ice cloud formatio

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

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

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

Equal abundance of summertime natural and wintertime anthropogenic Arctic organic aerosols

Organic aerosols in the Arctic are predominantly fuelled by anthropogenic sources in winter and natural sources in summer, according to observations from eight sites across the Arctic Aerosols play an important yet uncertain role in modulating the radiation balance of the sensitive Arctic atmosphere. Organic aerosol is one of the most abundant, yet least understood, fractions of the Arctic aerosol mass. Here we use data from eight observatories that represent the entire Arctic to reveal the annual cycles in anthropogenic and biogenic sources of organic aerosol. We show that during winter, the organic aerosol in the Arctic is dominated by anthropogenic emissions, mainly from Eurasia, which consist of both direct combustion emissions and long-range transported, aged pollution. In summer, the decreasing anthropogenic pollution is replaced by natural emissions. These include marine secondary, biogenic secondary and primary biological emissions, which have the potential to be important to Arctic climate by modifying the cloud condensation nuclei properties and acting as ice-nucleating particles. Their source strength or atmospheric processing is sensitive to nutrient availability, solar radiation, temperature and snow cover. Our results provide a comprehensive understanding of the current pan-Arctic organic aerosol, which can be used to support modelling efforts that aim to quantify the climate impacts of emissions in this sensitive region.Peer reviewe

Secondary organic aerosol formation from semi- and intermediate-volatility organic compounds and glyoxal: Relevance of O/C as a tracer for aqueous multiphase chemistry

International audienceThe role of aqueous multiphase chemistry in the formation of secondary organic aerosol (SOA) remains difficult to quantify. We investigate it here by testing the rapid formation of moderate oxygen-to-carbon (O/C) SOA during a case study in Mexico City. A novel laboratory-based glyoxal-SOA mechanism is applied to the field data, and explains why less gas-phase glyoxal mass is observed than predicted. Furthermore, we compare an explicit gas-phase chemical mechanism for SOA formation from semi- and intermediate-volatility organic compounds (S/IVOCs) with empirical parameterizations of S/IVOC aging. The mechanism representing our current understanding of chemical kinetics of S/IVOC oxidation combined with traditional SOA sources and mixing of background SOA underestimates the observed O/C by a factor of two at noon. Inclusion of glyoxal-SOA with O/C of 1.5 brings O/C predictions within measurement uncertainty, suggesting that field observations can be reconciled on reasonable time scales using laboratory-based empirical relationships for aqueous chemistry