Model-measurement consistency and limits of bioaerosol abundance over the continental United States

Due to low concentrations and chemical complexity, in situ observations of bioaerosol are geographically and temporally sparse, and this limits the accuracy of current emissions inventories. In this study, we apply a new methodology, including corrections for misidentification of mineral dust, to measurements of single particles over four airborne sampling campaigns to derive vertical profiles of bioaerosol over the continental United States. The new methodology is based on single-particle mass spectrometry (SPMS); it can extend historic datasets to include measurements of bioaerosol, it allows comparisons to other techniques, and it generally agrees with a global aerosol model. In the locations sampled, bioaerosols were at least a factor of 10 less abundant than mineral dust. Below 2 km, bioaerosol concentrations were measured between 6×103 and 2×104 m−3. Between 2 and 8 km, bioaerosol concentrations were between 0 and 2×104 m−3, and above 8 km, bioaerosol concentrations were between 0 and 1×103 m−3. Between 30 % and 80 % of single bioaerosol particles detected were internally mixed with dust. A direct comparison of the SPMS methodology with a co-located wideband integrated bioaerosol sensor (WIB) fluorescence sensor on a mountaintop site showed agreement to within a factor of 3 over the common size range

Negative responses of highland pines to anthropogenic activities in inland Spain: a palaeoecological perspective

Palaeoecological evidence indicates that highland pines were dominant in extensive areas of the mountains of Central and Northern Iberia during the first half of the Holocene. However, following several millennia of anthropogenic pressure, their natural ranges are now severely reduced. Although pines have been frequently viewed as first-stage successional species responding positively to human disturbance, some recent palaeobotanical work has proposed fire disturbance and human deforestation as the main drivers of this vegetation turnover. To assess the strength of the evidence for this hypothesis and to identify other possible explanations for this scenario, we review the available information on past vegetation change in the mountains of northern inland Iberia. We have chosen data from several sites that offer good chronological control, including palynological records with microscopic charcoal data and sites with plant macro- and megafossil occurrence. We conclude that although the available long-term data are still fragmentary and that new methods are needed for a better understanding of the ecological history of Iberia, fire events and human activities (probably modulated by climate) have triggered the pine demise at different locations and different temporal scales. In addition, all palaeoxylological, palynological and charcoal results obtained so far are fully compatible with a rapid human-induced ecological change that could have caused a range contraction of highland pines in western Iberia

Storminess as an explanation for the decline of pine woodland ca. 7,400 years ago at Loch Tulla, western Scotland

Pinus wood remains some 7,400 years old are abundantly preserved near the base of eroding peat at Clashgour, west of Loch Tulla on Rannoch Moor in western Scotland. Measurements are presented of the orientations of root systems in 42 in situ stumps, the direction of fall in 27 fallen trunks and the orientation (where direction of fall cannot be defined) in 40 fallen trunks. There are statistically significant orientations in the root systems, which suggests that the root structure of the trees had responded to stress from westerly winds. However, despite this the orientations and directions of fall in tree trunks, also statistically significant, show that many trees were probably blown over by strong westerly winds. The data suggest that increased precipitation and accelerated paludification are less likely explanations for tree loss at this site than a sudden demise through wind-throw

Detecting the provenance of Galapagos non-native pollen: The role of humans and air currents as transport mechanisms

The influence of non-native pollen, both long-distance transported and from introduced taxa, on reconstruction of past vegetation is not often well quantified in palynological investigations. We examined both fossil and modern samples from the Galápagos Islands, a remote archipelago lying 1000 km from the nearest continent. These islands are particularly well-suited for such an assessment, as (1) the native flora is limited and well-known, enabling increased taxonomic resolution within the palynological record, and (2) human impact in the Galápagos started after discovery by Europeans in 1535, allowing clear distinctions to be made between native and introduced taxa. Pollen samples were collected from five profiles in the Galápagos and grouped in (a) a pre-human-impact period, (b) an early human-impact period after c. 1535, and (c) a late human-impact period after c. 1973 when the introduced Cinchona pubescens tree started to expand. Introduced taxa accounted for approximately 10% of total pollen (excluding Cyperaceae) throughout the human-impact periods and long-distance transported pollen for approximately 5%. Twenty pollen taxa of introduced plants were found. Cinchona, which grows abundantly near the study sites, accounted for most of the introduced pollen, but an appreciable part also came from introduced plants growing in low numbers and at more distant locations within the archipelago. Total long-distance transported pollen (35 taxa) increased from 3% of total pollen in the pre-human-impact period to 5% in the human-impact periods, probably due to destruction of native vegetation through fire and thus reduction of local pollen production. These phenomena might lead to erroneous interpretation of local plant occurrence when the native/non-native or local/extra-local status of plants is not known. © The Author(s) 2012

Airborne measurements of organosulfates over the continental U.S.

Organosulfates are important secondary organic aerosol (SOA) components and good tracers for aerosol heterogeneous reactions. However, the knowledge of their spatial distribution, formation conditions, and environmental impact is limited. In this study, we report two organosulfates, an isoprene-derived isoprene epoxydiols (IEPOX) (2,3-epoxy-2-methyl-1,4-butanediol) sulfate and a glycolic acid (GA) sulfate, measured using the NOAA Particle Analysis Laser Mass Spectrometer (PALMS) on board the NASA DC8 aircraft over the continental U.S. during the Deep Convective Clouds and Chemistry Experiment (DC3) and the Studies of Emissions and Atmospheric Composition, Clouds, and Climate Coupling by Regional Surveys (SEAC4RS). During these campaigns, IEPOX sulfate was estimated to account for 1.4% of submicron aerosol mass (or 2.2% of organic aerosol mass) on average near the ground in the southeast U.S., with lower concentrations in the western U.S. (0.2-0.4%) and at high altitudes (<0.2%). Compared to IEPOX sulfate, GA sulfate was more uniformly distributed, accounting for about 0.5% aerosolmass on average, andmay bemore abundant globally. A number of other organosulfates were detected; nonewere as abundant as these two. Ambientmeasurements confirmed that IEPOX sulfate is formed from isoprene oxidation and is a tracer for isoprene SOA formation. The organic precursors of GA sulfatemay include glycolic acid and likely have both biogenic and anthropogenic sources. Higher aerosol acidity as measured by PALMS and relative humidity tend to promote IEPOX sulfate formation, and aerosol acidity largely drives in situ GA sulfate formation at high altitudes. This study suggests that the formation of aerosol organosulfates depends not only on the appropriate organic precursors but also on emissions of anthropogenic sulfur dioxide (SO2), which contributes to aerosol acidity