BackgroundEpidemiologic and health impact studies of fine particulate matter with diameter < 2.5 μm (PM2.5) are limited by the lack of monitoring data, especially in developing countries. Satellite...

http://fizz.phys.dal.ca/~atmos/publications/vanDonkelaar_2009_EHP.pdf

Global Estimates of Ambient Fine Particulate Matter Concentrations from Satellite-Based Aerosol Optical Depth: Development and Application

Forests emit large quantities of volatile organic compounds (VOCs) to the atmosphere. Their condensable oxidation products can form secondary organic aerosol, a significant and ubiquitous component of atmospheric aerosol, which is known to affect the Earth's radiation balance by scattering solar radiation and by acting as cloud condensation nuclei. The quantitative assessment of such climate effects remains hampered by a number of factors, including an incomplete understanding of how biogenic VOCs contribute to the formation of atmospheric secondary organic aerosol. The growth of newly formed particles from sizes of less than three nanometres up to the sizes of cloud condensation nuclei (about one hundred nanometres) in many continental ecosystems requires abundant, essentially non-volatile organic vapours, but the sources and compositions of such vapours remain unknown. Here we investigate the oxidation of VOCs, in particular the terpene α-pinene, under atmospherically relevant conditions in chamber experiments. We find that a direct pathway leads from several biogenic VOCs, such as monoterpenes, to the formation of large amounts of extremely low-volatility vapours. These vapours form at significant mass yield in the gas phase and condense irreversibly onto aerosol surfaces to produce secondary organic aerosol, helping to explain the discrepancy between the observed atmospheric burden of secondary organic aerosol and that reported by many model studies. We further demonstrate how these low-volatility vapours can enhance, or even dominate, the formation and growth of aerosol particles over forested regions, providing a missing link between biogenic VOCs and their conversion to aerosol particles. Our findings could help to improve assessments of biosphere-aerosol-climate feedback mechanisms, and the air quality and climate effects of biogenic emissions generally.

A large source of low-volatility secondary organic aerosol

https://nicholas.duke.edu/people/faculty/katul/AFM_LAW_2002.pdf

Environmental controls over carbon dioxide and water vapor exchange of terrestrial vegetation

Atmospheric aerosols exert an important influence on climate through their effects on stratiform cloud albedo and lifetime and the invigoration of convective storms. Model calculations suggest that almost half of the global cloud condensation nuclei in the atmospheric boundary layer may originate from the nucleation of aerosols from trace condensable vapours, although the sensitivity of the number of cloud condensation nuclei to changes of nucleation rate may be small. Despite extensive research, fundamental questions remain about the nucleation rate of sulphuric acid particles and the mechanisms responsible, including the roles of galactic cosmic rays and other chemical species such as ammonia. Here we present the first results from the CLOUD experiment at CERN. We find that atmospherically relevant ammonia mixing ratios of 100 parts per trillion by volume, or less, increase the nucleation rate of sulphuric acid particles more than 100–1,000-fold. Time-resolved molecular measurements reveal that nucleation proceeds by a base-stabilization mechanism involving the stepwise accretion of ammonia molecules. Ions increase the nucleation rate by an additional factor of between two and more than ten at ground-level galactic-cosmic-ray intensities, provided that the nucleation rate lies below the limiting ion-pair production rate. We find that ion-induced binary nucleation of H_(2)SO_(4)–H_(2)O can occur in the mid-troposphere but is negligible in the boundary layer. However, even with the large enhancements in rate due to ammonia and ions, atmospheric concentrations of ammonia and sulphuric acid are insufficient to account for observed boundary-layer nucleation.

/pdf/role-of-sulphuric-acid-ammonia-and-galactic-cosmic-rays-in-3k8is82upm.pdf

Role of sulphuric acid, ammonia and galactic cosmic rays in atmospheric aerosol nucleation

Published eddy covariance measurements of carbon dioxide (CO2) exchange between vegetation and the atmosphere from a global network are distilled, synthesised and reviewed according to time scale, climate and plant functional types, disturbance and land use. Other topics discussed include history of the network, errors and issues associated with the eddy covariance method, and a synopsis of how these data are being used by ecosystem and climate modellers and the remote-sensing community. Spatial and temporal differences in net annual exchange, FN, result from imbalances in canopy photosynthesis (FA) and ecosystem respiration (FR), which scale closely with one another on annual time scales. Key findings reported include the following: (1) ecosystems with the greatest net carbon uptake have the longest growing season, not the greatest FA; (2) ecosystems losing carbon were recently disturbed; (3) many old-growth forests act as carbon sinks; and (4) year-to-year decreases in FN are attributed to a suite of stresses that decrease FA and FR in tandem. Short-term flux measurements revealed emergent-scale processes including (1) the enhancement of light use efficiency by diffuse light, (2) dynamic pulses in FR following rain and (3) the acclimation FA and FR to temperature. They also quantify how FA and FR respond to droughts and heat spells.

/pdf/breathing-of-the-terrestrial-biosphere-lessons-learned-from-3gb2mq3tna.pdf

‘Breathing’ of the terrestrial biosphere: lessons learned from a global network of carbon dioxide flux measurement systems

We planned and implemented the SMEAR II and I measuring systems to measure material and energy fluxes between forest ecosystem and its surroundings and within the ecosystem. In addition, we measured the processes generating the fluxes and environmental factors affecting the processes. We constructed SMEAR I in 1991 and SMEAR II in 1994–1996. The mass and energy fluxes play an important role in our physical and physiological theory of forest ecology. The construction principle of SMEAR measuring stations is coherent with our theory, and this is why the data obtained at SMEAR stations have been useful in the development and testing of our theory.

Station for Measuring Ecosystem-Atmosphere Relations: SMEAR

A new particle size magnifier (PSM) for detection of nano-CN as small as ∼1 nm in mobility diameter was developed, calibrated and tested in atmospheric measurements. The working principle of a PSM is to mix turbulently cooled sample flow with heated clean air flow saturated by the working fluid. This provides a high saturation ratio for the working fluid and activates the seed particles and grows them by condensation of the working fluid. In order to reach high saturation ratios, and thus to activate nano-CN without homogeneous nucleation, diethylene glycol was chosen as the working fluid. The PSM was able to grow nano-CN to mean diameter of 90 nm, after which an ordinary condensation particle counter was used to count the grown particles (TSI 3010). The stability of the PSM was found to be good making it suitable for stand-alone field measurements. Calibration results show that the detection efficiency of the prototype PSM + TSI 3010 for charged tetra-alkyl ammonium salt molecules having mobility equival...

Particle Size Magnifier for Nano-CN Detection

Long-term field measurements of atmosphere-surface interactions in boreal forest combining forest ecology, micrometeorology, aerosol physics and atmospheric chemistry

Long-term measurements of fluxes of sensible heat ( H ), latent heat ( LE ) and carbon dioxide ( F c ) were made from December 2005 to August 2006 over an urban landscape in Helsinki, Finland using the direct micrometeorological eddy covariance technique. Three distinguished sectors of land-use cover (vegetation, roads and buildings) allowed comparisons of fluxes over different urban surfaces. The normalized standard deviation of wind and scalars as a function of atmospheric stability were typical for rough surfaces, as were turbulence spectra and cospectra. Footprint analysis was performed by a boundary-layer one and half-order closure model allowing for discrimination of surface and canopy sinks/sources and complex topography. Fluxes were analysed as average diurnal courses over winter, spring and summer periods. H exceeded LE reaching 300 W m -2 over urban and road surfaces in the summer and it was close to 100 W m -2 in the winter. LE was highest in the summer over vegetation cover attaining 150 W m -2 . The emission rate of CO 2 was high over road sector [20 μ mol (m2s) -1 ][Correction added after online publication 16 Oct 2007: 30 μ mol changed to 20 μ mol] while in the vegetation sector it remained below 5 μ mol (m2s) -1 and at summertime reached even −10 μ mol(m2 s) -1 [Correction added after online publication 16 Oct 2007: wording of sentence altered]. Effluxes from soil measured by chambers were 1–3 μ mol (m2s) -1 . F c correlated with traffic density and a background non-vehicle flux was 1 μ mol (m2s)−1[Correction added after online publication 16 Oct 2007: 2 μ mol changed to 1 μ mol]. DOI: 10.1111/j.1600-0889.2007.00312.x

Surface-atmosphere interactions over complex urban terrain in Helsinki, Finland

We present results from the air pollution and turbulent exchange measurements made at the urban measurement station SMEAR III in Helsinki, Finland. First measurements at the station started in August 2004 and since then more measurements have gradually been added. We analyze data until June 2007. Temporal variations and dependencies between the size-fractionated particle number concentrations (both fine and coarse particle concentrations), gas concentrations (O 3 , NO x , CO and SO 2 ), turbulent fluxes of momentum, sensible and latent heat and CO 2 , and meteorological variables were studied. Most of the air pollutants and turbulent fluxes showed distinct annual and diurnal variation closely related to the local combustion sources (especially traffic) and the amount of available solar radiation. Ultrafine particles showed the most explicit dependence on traffic and traffic-related pollutants, while larger particles were more affected by the meteorological conditions. The surface fluxes were strongly affected by the specific conditions in urban environment.

Erkki Siivola

Papers

Station for Measuring Ecosystem-Atmosphere Relations: SMEAR

Particle Size Magnifier for Nano-CN Detection

Long-term field measurements of atmosphere-surface interactions in boreal forest combining forest ecology, micrometeorology, aerosol physics and atmospheric chemistry

Surface-atmosphere interactions over complex urban terrain in Helsinki, Finland

The urban measurement station SMEAR III: Continuous monitoring of air pollution and surface-atmosphere interactions in Helsinki, Finland