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In-situ observations of young contrails – overview and selected results from the CONCERT campaign

Lineshaped contrails were detected with the research aircraft Falcon during the CONCERT – CONtrail and Cirrus ExpeRimenT – campaign in October/November 2008. The Falcon was equipped with a set of instruments to measure the particle size distribution, shape, extinction and chemical composition as well as trace gas mixing ratios of sulfur dioxide (SO2), reactive nitrogen and halogen species (NO, NOy, HNO3, HONO, HCl), ozone (O3) and carbon monoxide (CO). During 12 mission flights over Europe, numerous contrails, cirrus clouds and a volcanic aerosol layer were probed at altitudes between 8.5 and 11.6 km and at temperatures above 213 K. 22 contrails from 11 different aircraft were observed near and below ice saturation. The observed NO mixing ratios, ice crystal and soot number densities are compared to a process based contrail model. On 19 November 2008 the contrail from a CRJ-2 aircraft was penetrated in 10.1 km altitude at a temperature of 221 K. The contrail had mean ice crystal number densities of 125 cm−3 with effective radii reff of 2.6 μm. The presence of particles with r>50 μm in the less than 2 min old contrail suggests that natural cirrus crystals were entrained in the contrail. Mean HONO/NO (HONO/NOy) ratios of 0.037 (0.024) and the fuel sulfur conversion efficiency to H2SO4 (εS↓) of 2.9 % observed in the CRJ-2 contrail are in the range of previous measurements in the gaseous aircraft exhaust. On 31 October 2010 aviation NO emissions could have contributed by more than 40% to the regional scale NO levels in the mid-latitude lowest stratosphere. The CONCERT observations help to better quantify the climate impact from contrails and will be used to investigate the chemical processing of trace gases on contrails.
Impact of Manaus City on the Amazon Green Ocean atmosphere: ozone production, precursor sensitivity and aerosol load

As a contribution to the Large-Scale Biosphere-Atmosphere Experiment in Amazonia – Cooperative LBA Airborne Regional Experiment (LBA-CLAIRE-2001) field campaign in the heart of the Amazon Basin, we analyzed the temporal and spatial dynamics of the urban plume of Manaus City during the wet-to-dry season transition period in July 2001. During the flights, we performed vertical stacks of crosswind transects in the urban outflow downwind of Manaus City, measuring a comprehensive set of trace constituents including O3, NO, NO2, CO, VOC, CO2, and H2O. Aerosol loads were characterized by concentrations of total aerosol number (CN) and cloud condensation nuclei (CCN), and by light scattering properties. Measurements over pristine rainforest areas during the campaign showed low levels of pollution from biomass burning or industrial emissions, representative of wet season background conditions. The urban plume of Manaus City was found to be joined by plumes from power plants south of the city, all showing evidence of very strong photochemical ozone formation. One episode is discussed in detail, where a threefold increase in ozone mixing ratios within the atmospheric boundary layer occurred within a 100 km travel distance downwind of Manaus. Observation-based estimates of the ozone production rates in the plume reached 15 ppb h−1. Within the plume core, aerosol concentrations were strongly enhanced, with ΔCN/ΔCO ratios about one order of magnitude higher than observed in Amazon biomass burning plumes. ΔCN/ΔCO ratios tended to decrease with increasing transport time, indicative of a significant reduction in particle number by coagulation, and without substantial new particle nucleation occurring within the time/space observed. While in the background atmosphere a large fraction of the total particle number served as CCN (about 60–80% at 0.6% supersaturation), the CCN/CN ratios within the plume indicated that only a small fraction (16±12%) of the plume particles were CCN. The fresh plume aerosols showed relatively weak light scattering efficiency. The CO-normalized CCN concentrations and light scattering coefficients increased with plume age in most cases, suggesting particle growth by condensation of soluble organic or inorganic species. We used a Single Column Chemistry and Transport Model (SCM) to infer the urban pollution emission fluxes of Manaus City, implying observed mixing ratios of CO, NOx and VOC. The model can reproduce the temporal/spatial distribution of ozone enhancements in the Manaus plume, both with and without accounting for the distinct (high NOx) contribution by the power plants; this way examining the sensitivity of ozone production to changes in the emission rates of NOx. The VOC reactivity in the Manaus region was dominated by a high burden of biogenic isoprene from the background rainforest atmosphere, and therefore NOx control is assumed to be the most effective ozone abatement strategy. Both observations and models show that the agglomeration of NOx emission sources, like power plants, in a well-arranged area can decrease the ozone production efficiency in the near field of the urban populated cores. But on the other hand remote areas downwind of the city then bear the brunt, being exposed to increased ozone production and N-deposition. The simulated maximum stomatal ozone uptake fluxes were 4 nmol m−2 s−1 close to Manaus, and decreased only to about 2 nmol m−2 s−1 within a travel distance >1500 km downwind from Manaus, clearly exceeding the critical threshold level for broadleaf trees. Likewise, the simulated N deposition close to Manaus was ~70 kg N ha−1 a−1 decreasing only to about 30 kg N ha−1 a−1 after three days of simulation.
Role of dust alkalinity in acid mobilization of iron

Atmospheric processing of mineral aerosols by acid gases (e.g., SO2, HNO3, N2O5, and HCl) may play a key role in the transformation of insoluble iron (Fe in the oxidized or ferric (III) form) to soluble forms (e.g., Fe(II), inorganic soluble species of Fe(III), and organic complexes of iron). On the other hand, mineral dust particles have a potential of neutralizing the acidic species due to the alkaline buffer ability of carbonate minerals (e.g., CaCO3 and MgCO3). Here we demonstrate the impact of dust alkalinity on the acid mobilization of iron in a three-dimensional aerosol chemistry transport model that includes a mineral dissolution scheme. In our model simulations, most of the alkaline dust minerals cannot be entirely consumed by inorganic acids during the transport across the North Pacific Ocean. As a result, the inclusion of alkaline compounds in aqueous chemistry substantially limits the iron dissolution during the long-range transport to the North Pacific Ocean: only a small fraction of iron (<0.2%) dissolves from hematite in the coarse-mode dust aerosols with 0.45% soluble iron initially. On the other hand, a significant fraction of iron (1–2%) dissolves in the fine-mode dust aerosols due to the acid mobilization of the iron-containing minerals externally mixed with carbonate minerals. Consequently, the model quantitatively reproduces higher iron solubility in smaller particles as suggested by measurements over the Pacific Ocean. It implies that the buffering effect of alkaline content in dust aerosols might help to explain the inverse relationship between aerosol iron solubility and particle size. We also demonstrate that the iron solubility is sensitive to the chemical specification of iron-containing minerals in dust. Compared with the dust sources, soluble iron from combustion sources contributes to a relatively marginal effect for deposition of soluble iron over the North Pacific Ocean during springtime. Our results suggest that more comprehensive data for chemical specificity of iron-rich dust is needed to improve the predictive capability for size-segregated soluble iron particles.
On the impacts of phytoplankton-derived organic matter on the properties of the primary marine aerosol – Part 1: Source fluxes

The effect of biogenic dissolved and colloidal organic matter on the production of submicron primary sea-spray aerosol was investigated via the simulation of bubble bursting in seawater enriched with phytoplankton-released organics. Seawater samples collected along a transect off the West African coast during the RHaMBLe cruise (RRS Discovery cruise D319), conducted as part of the SOLAS UK program, were analysed in order to identify the dominant oceanic algal species in a region of high biological activity. Cultures of microalgal strains representative of the species found in the collected seawater were grown in order to produce natural bioexudate. Colloidal plus dissolved organic fraction in this material remaining after <0.2 μm filtration was employed to prepare organic-enriched seawater proxies for the laboratory production of marine aerosol using a plunging-waterjet system as an aerosol generator. Submicron size distributions of aerosols generated from different organic monolayers and seawater proxies enriched with biogenic exudate were measured and compared with blanks performed with artificial seawater devoid of marine organics. A shift of the aerosol submicron size distribution toward smaller sizes and an increase in the production of particles with dry diameter (Dp0)<100 nm was repeatedly observed with increasing amounts of diatomaceous bioexudate in the seawater proxies used for aerosol generation. The effect was found to be sensitive to the organic carbon concentration in seawater and the algal exudate type. Diatomaceous exudate with organic carbon concentration (OC<0.2 μm) >175 μM was required to observe a significant impact on the size distribution, which implies that effects are expected to be substantial only in high biological activity areas abundant with diatom algal populations. The laboratory findings were in agreement with analogous bubble-bursting experiments conducted with unfiltered oceanic seawater collected during the RHaMBLe cruise, which revealed a higher production of particles with Dp0<100 nm at regions with high biological activity. These findings suggest that the increase in the atmospheric aerosol modal sizes from winter to summer, reported by long-term observations in North Atlantic waters, is not directly due to an impact of the higher primary organic matter production occurring during warm periods. A novel sub-micrometric size-resolved source flux function, explicitly defined as a function of the diatomaceous exudate concentration, was derived from the size distribution measurements and the estimation of the fractional whitecap coverage. According to the defined parameterisation, a 300 μM OC<0.2 μm concentration of diatomaceous exudate in seawater produces an overall increment in the total source particle flux of ~20% with respect to the organics-free seawater case. The effect increases with decreasing particle size for Dp0<100 nm, resulting in multiplicative factors between 1.02–2 with respect to the particle flux generated from seawater devoid of marine organics. The total source flux derived from the presented parameterisation was compared to recent definitions of sea-spray source fluxes based on laboratory and field observations in the literature.
Chemistry of rain events in West Africa: evidence of dust and biogenic influence in convective systems

This paper documents the chemical composition of 7 rain events associated with mesoscale convective systems sampled at the supersite of Banizoumbou, Niger, during the first special observation periods (June–July 2006) of the African Monsoon Multidisciplinary Analyses (AMMA) experiment. Time-resolved rain sampling was performed in order to discriminate the local dust scavenged at the beginning of rain event from the aerosol particles incorporated in the cloud at the end of the rain. The total elemental composition is dominated by Al, Si, Fe and Ca, indicating a high influence of dust and limited marine or anthropogenic contribution. After the aerosol wash-out, the elemental concentrations normalized to Al and the microscopic observations of diatoms, a tracer of the Bodélé depression, both indicate that the total elemental composition of rainwater is controlled by dust originating from North-eastern Saharan sources and probably incorporated in the convective cloud from the Harmattan layer. The low variability of the rain composition over the measurement period indicates a regional and temporal homogeneity of dust composition in the Harmattan layer. In the dissolved phase, the dominant anions are nitrate (NO3−), sulphate (SO42−) and chloride (Cl−). However, between June and July we observe an increasing contribution of the organic anions (formate, acetate, oxalate) associated with biogenic emissions to the total ion composition. These results confirm the large influence of biogenic emissions on the rain composition over Sahel during the wet season. The paper concludes on the capacity of mesoscale convective systems to carry simultaneously dust and biogenic compounds originating from different locations and depose them jointly. It also discusses the potential biogeochemical impact of such a phenomenon.
Polar organic marker compounds in atmospheric aerosols during the LBA-SMOCC 2002 biomass burning experiment in Rondônia, Brazil: sources and source processes, time series, diel variations and size distributions

Measurements of polar organic marker compounds were performed on aerosols that were collected at a pasture site in the Amazon basin (Rondônia, Brazil) using a high-volume dichotomous sampler (HVDS) and a Micro-Orifice Uniform Deposit Impactor (MOUDI) within the framework of the 2002 LBA-SMOCC (Large-Scale Biosphere Atmosphere Experiment in Amazônia – Smoke Aerosols, Clouds, Rainfall, and Climate: Aerosols From Biomass Burning Perturb Global and Regional Climate) campaign. The campaign spanned the late dry season (biomass burning), a transition period, and the onset of the wet season (clean conditions). In the present study a more detailed discussion is presented compared to previous reports on the behavior of selected polar marker compounds, including levoglucosan, malic acid, isoprene secondary organic aerosol (SOA) tracers and tracers for fungal spores. The tracer data are discussed taking into account new insights that recently became available into their stability and/or aerosol formation processes. During all three periods, levoglucosan was the most dominant identified organic species in the PM2.5 size fraction of the HVDS samples. In the dry period levoglucosan reached concentrations of up to 7.5 μg m−3 and exhibited diel variations with a nighttime prevalence. It was closely associated with the PM mass in the size-segregated samples and was mainly present in the fine mode, except during the wet period where it peaked in the coarse mode. Isoprene SOA tracers showed an average concentration of 250 ng m−3 during the dry period versus 157 ng m−3 during the transition period and 52 ng m−3 during the wet period. Malic acid and the 2-methyltetrols exhibited a different size distribution pattern, which is consistent with different aerosol formation processes (i.e., gas-to-particle partitioning in the case of malic acid and heterogeneous formation from gas-phase precursors in the case of the 2-methyltetrols). The 2-methyltetrols were mainly associated with the fine mode during all periods, while malic acid was prevalent in the fine mode only during the dry and transition periods, and dominant in the coarse mode during the wet period. The sum of the fungal spore tracers arabitol, mannitol, and erythritol in the PM2.5 fraction of the HVDS samples during the dry, transition, and wet periods was, on average, 54 ng m−3, 34 ng m−3, and 27 ng m−3, respectively, and revealed minor day/night variation. The mass size distributions of arabitol and mannitol during all periods showed similar patterns and an association with the coarse mode, consistent with their primary origin. The results show that even under the heavy smoke conditions of the dry period a natural background with contributions from bioaerosols and isoprene SOA can be revealed. The enhancement in isoprene SOA in the dry season is mainly attributed to an increased acidity of the aerosols, increased NOx concentrations and a decreased wet deposition.
Long-term trends of black carbon and sulphate aerosol in the Arctic: changes in atmospheric transport and source region emissions

As a part of the IPY project POLARCAT (Polar Study using Aircraft, Remote Sensing, Surface Measurements and Models, of Climate, Chemistry, Aerosols and Transport) and building on previous work (Hirdman et al., 2010), this paper studies the long-term trends of both atmospheric transport as well as equivalent black carbon (EBC) and sulphate for the three Arctic stations Alert, Barrow and Zeppelin. We find a general downward trend in the measured EBC concentrations at all three stations, with a decrease of −2.1±0.4 ng m−3 yr−1 (for the years 1989–2008) and −1.4±0.8 ng m−3 yr−1 (2002–2009) at Alert and Zeppelin respectively. The decrease at Barrow is, however, not statistically significant. The measured sulphate concentrations show a decreasing trend at Alert and Zeppelin of −15±3 ng m−3 yr−1 (1985–2006) and −1.3±1.2 ng m−3 yr−1 (1990–2008) respectively, while there is no trend detectable at Barrow. To reveal the contribution of different source regions on these trends, we used a cluster analysis of the output of the Lagrangian particle dispersion model FLEXPART run backward in time from the measurement stations. We have investigated to what extent variations in the atmospheric circulation, expressed as variations in the frequencies of the transport from four source regions with different emission rates, can explain the long-term trends in EBC and sulphate measured at these stations. We find that the long-term trend in the atmospheric circulation can only explain a minor fraction of the overall downward trend seen in the measurements of EBC (0.3–7.2%) and sulphate (0.3–5.3%) at the Arctic stations. The changes in emissions are dominant in explaining the trends. We find that the highest EBC and sulphate concentrations are associated with transport from Northern Eurasia and decreasing emissions in this region drive the downward trends. Northern Eurasia (cluster: NE, WNE and ENE) is the dominant emission source at all Arctic stations for both EBC and sulphate during most seasons. In wintertime, there are indications that the EBC emissions from the eastern parts of Northern Eurasia (ENE cluster) have increased over the last decade.
New particle formation and ultrafine charged aerosol climatology at a high altitude site in the Alps (Jungfraujoch, 3580 m a.s.l., Switzerland)

We investigate the formation and growth of charged aerosols clusters at Jungfraujoch, in the Swiss Alps (3580 m a.s.l.), the highest altitude site of the European EUCAARI project intensive campaign. Charged particles and clusters (0.5–1.8 nm) were measured from April 2008 to April 2009 and allowed the detection of nucleation events in this very specific environment (presence of free tropospheric air and clouds). We found that the naturally charged aerosol concentrations, which are dominated by the cluster size class, shows a strong diurnal pattern likely linked to valley breezes transporting surface layer ion precursors, presumably radon. Cosmic rays were found not to be the major ion source at the measurement site. However, at night, when air masses are more representative of free tropospheric conditions, we found that the cluster concentrations are still high. The charged aerosol size distribution and concentration are strongly influenced by the presence of clouds at the station. Clouds should be taken into account when deriving high altitude nucleation statistics. New particle formation occurs on average 17.5% of the measurement period and shows a weak seasonality with a minimum of frequency during winter, but this seasonality is enhanced when the data set is screened for periods when the atmospheric station is out of clouds. The role of ions in the nucleation process was investigated and we found that the ion-mediated nucleation explains 22.3% of the particle formation. The NPF events frequency is correlated with UV radiation but not with calculated H2SO4 concentrations, suggesting that other compounds such as organic vapors are involved in the nucleation and subsequently growth process. In fact, NPF events frequency also surprisingly increases with the condensational sink (CS), suggesting that at Jungfraujoch, the presence of condensing vapours probably coupled with high CS are driving the occurrence of NPF events. A strong link to the air mass path was also pointed out and events were observed to be frequently occurring in Eastern European air masses, which present the highest condensational sink. In these air masses, pre-existing cluster concentrations are more than three time larger than in other air masses during event days, and no new clusters formation is observed, contrarily to what is happening in other air mass types.
Terpenylic acid and related compounds: precursors for dimers in secondary organic aerosol from the ozonolysis of α- and β-pinene

In the present study, we have characterized the structure of a higher-molecular weight (MW) 358 α- and β-pinene dimeric secondary organic aerosol (SOA) product that received ample attention in previous molecular characterization studies and has been elusive. Based on mass spectrometric evidence for deprotonated molecules formed by electrospray ionization in the negative ion mode and chemical considerations, it is suggested that diaterpenylic acid is a key monomeric intermediate for dimers of the ester type. It is proposed that cis-pinic acid is esterified with the hydroxyl-containing diaterpenylic acid, which can be explained through acid-catalyzed hydrolysis of the recently elucidated lactone-containing terpenylic acid and/or diaterpenylic acid acetate, both first-generation oxidation products. To a minor extent, higher-MW 358 and 344 diester products are formed containing other terpenoic acids as monomeric units, i.e., diaterpenylic acid instead of cis-pinic acid, and diaterebic acid instead of diaterpenylic acid. It is shown that the MW 358 diester and related MW 344 compounds, which can be regarded as processed SOA products, also occur in ambient fine (PM2.5) rural aerosol collected at night during the warm period of the 2006 summer field campaign conducted at K-puszta, Hungary, a rural site with coniferous vegetation. This indicates that, under ambient conditions, the higher-MW diesters are formed in the particle phase over a longer time-scale than that required for gas-to-particle partitioning of their monomeric precursors in laboratory α-/β-pinene ozonolysis experiments.
Aerosol fluxes and dynamics within and above a tropical rainforest in South-East Asia

Atmospheric aerosol measurements were conducted near Danum Valley, in the Malaysian state of Sabah, North-East Borneo, as part of the OP3 and ACES projects, in April and June/July 2008. Here, aerosol fluxes and diurnal variability in and above the rainforest canopy were examined in order to gain an understanding of their behaviour in the surface layer of the South-East Asian rainforest. Aerosol fluxes were calculated by eddy covariance from measurements above the rainforest canopy on the Global Atmosphere Watch (GAW) tower. Upward fluxes were seen on most mornings between 09:00 and 11:00 local time and this could be attributed to venting of the nocturnal boundary layer as it broke up in the morning. Measurements were also conducted within the canopy and trunk space at a nearby site. Profiles in aerosol number concentrations were investigated using GRIMM Optical Particle Counters (OPCs) at various levels within the rainforest canopy and trunk space, as well as a single OPC on a vertically moving platform. These showed an overnight increase in larger particles (1–20 μm) at all levels, but much more prominently near the top of the canopy, which could be attributed to fog formation. At ground level, number concentrations in this size range correlated with enhancements in biological aerosol concentrations, measured using a Wide Issue Bioaerosol Spectrometer (WIBS) located near the forest floor, suggesting that coarse particle number concentrations were dominated by biological aerosols. A comparison of particle number concentrations (in the size range 0.5–1.0 μm) between above canopy and the trunk space showed correlations, despite turbulence data suggesting persistent decoupling between the two measurement sites. These correlations often relied on a shift of the particle time-series against each other, implying a time delay in observations between the sites, which varied according to time of day. This lag time was shortest during the middle of the day by a significant margin. This was not observed for aerosols larger than 1.0 μm. Further evidence of daytime coupling between above canopy and the trunk space in terms of aerosol measurements is implied by comparison of measurements from an Aerosol Mass Spectrometer (AMS) at the GAW tower and simultaneous bag sampling at the in-canopy site, subsequently analysed with the AMS. Transport of particles through the canopy seems to occur through large-scale, sporadic turbulent events, suggesting that the coupling between the canopy space and the air above is due to these ventilation events.