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Passenger aircraft project CARIBIC 1997–2002, Part II: the ventilation of the lowermost stratosphere
Passenger aircraft project CARIBIC 1997–2002, Part I: the extratropical chemical tropopause
Interaction of aerosol particles composed of protein and saltswith water vapor: hygroscopic growth and microstructural rearrangement

The interaction of aerosol particles composed of the protein bovine serum albumin (BSA) and the inorganic salts sodium chloride and ammonium nitrate with water vapor has been investigated by hygroscopicity tandem differential mobility analyzer (H-TDMA) experiments complemented by transmission electron microscopy (TEM) and Köhler theory calculations (100-300nm particle size range, 298K, 960hPa). BSA was chosen as a well-defined model substance for proteins and other macromolecular compounds, which constitute a large fraction of the water-soluble organic component of air particulate matter. Pure BSA particles exhibited deliquescence and efflorescence transitions at <IMG WIDTH="15" HEIGHT="15" ALIGN="BOTTOM" BORDER="0" src="acp-4-323-img1.gif" ALT="$sim$">35% relative humidity (<IMG WIDTH="30" HEIGHT="14" ALIGN="BOTTOM" BORDER="0" src="acp-4-323-img2.gif" ALT="$RH$">) and a hygroscopic diameter increase by up to <IMG WIDTH="15" HEIGHT="15" ALIGN="BOTTOM" BORDER="0" src="acp-4-323-img1.gif" ALT="$sim$">10% at 95% <IMG WIDTH="30" HEIGHT="14" ALIGN="BOTTOM" BORDER="0" src="acp-4-323-img2.gif" ALT="$RH$"> in good agreement with model calculations based on a simple parameterisation of the osmotic coefficient. Pure NaCl particles were converted from near-cubic to near-spherical shape upon interaction with water vapor at relative humidities below the deliquescence threshold (partial surface dissolution and recrystallisation), and the diameters of pure NH4NO3 particles decreased by up to 10% due to chemical decomposition and evaporation. Mixed NaCl-BSA and NH4NO3-BSA particles interacting with water vapor exhibited mobility equivalent diameter reductions of up to 20%, depending on particle generation, conditioning, size, and chemical composition (BSA dry mass fraction 10-90%). These observations can be explained by formation of porous agglomerates (envelope void fractions up to 50%) due to ion-protein interactions and electric charge effects on the one hand, and by compaction of the agglomerate structure due to capillary condensation effects on the other. The size of NH4NO3-BSA particles was apparently also influenced by volatilisation of NH4NO3, but not as much as for pure salt particles, i.e. the protein inhibited the decomposition of NH4NO3 or the evaporation of the decomposition products NH3 and HNO3. The efflorescence threshold of NaCl-BSA particles decreased with increasing BSA dry mass fraction, i.e. the protein inhibited the formation of salt crystals and enhanced the stability of supersaturated solution droplets. The H-TDMA and TEM results indicate that the protein was enriched at the surface of the mixed particles and formed an envelope, which inhibits the access of water vapor to the particle core and leads to kinetic limitations of hygroscopic growth, phase transitions, and microstructural rearrangement processes. The Köhler theory calculations performed with different types of models demonstrate that the hygroscopic growth of particles composed of inorganic salts and proteins can be efficiently described with a simple volume additivity approach, provided that the correct dry solute mass equivalent diameter and composition are known. A parameterisation for the osmotic coefficient of macromolecular substances has been derived from an osmotic pressure virial equation. For its application only the density and molar mass of the substance have to be known or estimated, and it is fully compatible with traditional volume additivity models for salt mixtures.
The vertical distribution of aerosols, Saharan dust and cirrus clouds in Rome (Italy) in the year 2001

A set of 813 lidar profiles of tropospheric aerosol and cirrus clouds extinction and depolarization observed in Rome, Italy, between February 2001 and February 2002 is analyzed and discussed. The yearly record reveals a meaningful contribution of both cirrus clouds (38%) and Saharan dust (12%) to the total optical thickness (OT) of 0.26, at 532nm. Seasonal analysis shows the planetary boundary layer (PBL) aerosols to be confined below 2km in winter and 3.8km in summer, with relevant OT shifting from 0.08 to 0.16, respectively. Cirrus clouds maximise in spring and autumn, in both cases with average OT similar to the PBL aerosols one. With the exception of winter months, Saharan dust is found to represent an important third layer mostly residing between PBL aerosols and cirrus clouds, with yearly average OT<IMG WIDTH="15" HEIGHT="15" ALIGN="BOTTOM" BORDER="0" src="acp-4-351-img1.gif" ALT="$approx$">0.03. Saharan dust and cirrus clouds were detected in 20% and in 45% of the observational days, respectively. Validation of the lidar OT retrievals against collocated sunphotometer observations show very good agreement. These results represent one of the few yearly records of tropospheric aerosol vertical profiles available in the literature.
Space-borne observations link the tropical atlantic ozone maximum and paradox to lightning

The potential enhancement of tropospheric column ozone values over the Tropical Atlantic Ocean on a seasonal basis by lightning is investigated using satellite derived ozone data, TRMM lightning data, ozonesonde data and NCEP reanalysis during 1998-2001. Our results show that the number of lightning flashes in Africa and South America reach a maximum during September, October and November (SON). The spatial patterns of winds in combination with lightning from West Africa, Central Africa and South America is likely responsible for enriching middle/upper troposphere ozone over the Tropical South Atlantic during SON. Moreover, lightning flashes are high in the hemisphere opposite to biomass burning during December, January, and February (DJF) and June, July and August (JJA). This pattern leads to an enrichment of ozone in the middle/upper troposphere in the Southern Hemisphere Tropics during DJF and the Northern Hemisphere Tropics during JJA. During JJA the largest numbers of lightning flashes are observed in West Africa, enriching tropospheric column ozone to the north of 5<IMG WIDTH="10" HEIGHT="16" ALIGN="BOTTOM" BORDER="0" src="acp-4-361-img1.gif" ALT="$^circ$">S in the absence of biomass burning. During DJF, lightning is concentrated in South America and Central Africa enriching tropospheric column ozone south of the Equator in the absence of biomass burning.
Measurements of the sum of HO2NO2 and CH3O2NO2 in the remote troposphere

The chemistry of peroxynitric acid (HO2NO2) and methyl peroxynitrate (CH3O2NO2)is predicted to be particularly important in the upper troposphere where temperatures are frequently low enough that these compounds do not rapidly decompose. At temperatures below 240K, we calculate that about 20% of NOy in the mid- and high-latitude upper troposphere is HO2NO2. Under these conditions, the reaction of OH with HO2NO2 is estimated to account for as much as one third of the permanent loss of hydrogen radicals. During the Tropospheric Ozone Production about the Spring Equinox (TOPSE) campaign, we used thermal dissociation laser-induced fluorescence (TD-LIF) to measure the sum of peroxynitrates (<IMG WIDTH="15" HEIGHT="14" ALIGN="BOTTOM" BORDER="0" src="acp-4-377-img4.gif" ALT="$Sigma$">PNs<IMG WIDTH="15" HEIGHT="13" ALIGN="BOTTOM" BORDER="0" src="acp-4-377-img5.gif" ALT="$equiv$"> HO2NO2+CH3O2NO2+PAN+PPN+...) aboard the NCAR C-130 research aircraft. We infer the sum of HO2NO2 and CH3O2NO2 as the difference between <IMG WIDTH="15" HEIGHT="14" ALIGN="BOTTOM" BORDER="0" src="acp-4-377-img4.gif" ALT="$Sigma$">PN measurements and gas chromatographic measurements of the two major peroxy acyl nitrates, peroxy acetyl nitrate (PAN) and peroxy propionyl nitrate (PPN). Comparison with NOy and other nitrogen oxide measurements confirms the importance of HO2NO2 and CH3O2NO2 to the reactive nitrogen budget and shows that current thinking about the chemistry of these species is approximately correct. During the spring high latitude conditions sampled during the TOPSE experiment, the model predictions of the contribution of (HO2NO2+CH3O2NO2) to NOy are highly temperature dependent: on average 30% of NOy at 230K, 15% of NOy at 240K, and <IMG WIDTH="15" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" src="acp-4-377-img7.gif" ALT="$<$">5% of NOy above 250K. The temperature dependence of the inferred concentrations corroborates the contribution of overtone photolysis to the photochemistry of peroxynitric acid. A model that includes IR photolysis (J=1x10-5s-1) agreed with the observed sum of HO2NO2+CH3O2NO2 to better than 35% below 240K where the concentration of these species is largest.
Formation of binary ion clusters from polar vapours: effect of the dipole-charge interaction

Formation of binary cluster ions from polar vapours is considered. The effect of vapour polarity on the size and composition of the critical clusters is investigated theoretically and a corrected version of classical Kelvin-Thomson theory of binary ion-induced nucleation is derived. The model predictions of the derived theory are compared to the results given by classical binary homogeneous nucleation theory and ion-induced nucleation theory. The calculations are performed in wide range of the ambient conditions for a system composed of sulfuric acid and water vapour. It is shown that dipole-charge interaction significantly decreases the size of the critical clusters, especially under the atmospheric conditions when the size of critical clusters is predicted to be small.
Urban aerosol number size distributions

Aerosol number size distributions have been measured since 5 May 1997 in Helsinki, Finland. The presented aerosol data represents size distributions within the particle diameter size range 8-400nm during the period from May 1997 to March 2003. The daily, monthly and annual patterns of the aerosol particle number concentrations were investigated. The temporal variation of the particle number concentration showed close correlations with traffic activities. The highest total number concentrations were observed during workdays; especially on Fridays, and the lowest concentrations occurred during weekends; especially Sundays. Seasonally, the highest total number concentrations were observed during winter and spring and lower concentrations were observed during June and July. More than 80% of the number size distributions had three modes: nucleation mode (<IMG WIDTH="36" HEIGHT="30" ALIGN="MIDDLE" BORDER="0" src="acp-4-391-img1.gif" ALT="$D_{p}{<}$">30nm), Aitken mode (20-100nm) and accumulation mode (<IMG WIDTH="36" HEIGHT="30" ALIGN="MIDDLE" BORDER="0" src="acp-4-391-img2.gif" ALT="$D_{p}{>}$">90nm). Less than 20% of the number size distributions had either two modes or consisted of more than three modes. Two different measurement sites were used; in the first (Siltavuori, 5.5.1997-5.3.2001), the arithmetic means of the particle number concentrations were 7000cm<IMG WIDTH="20" HEIGHT="18" ALIGN="BOTTOM" BORDER="0" src="acp-4-391-img3.gif" ALT="$^{-3}$">, 6500cm<IMG WIDTH="20" HEIGHT="18" ALIGN="BOTTOM" BORDER="0" src="acp-4-391-img3.gif" ALT="$^{-3}$">, and 1000cm<IMG WIDTH="20" HEIGHT="18" ALIGN="BOTTOM" BORDER="0" src="acp-4-391-img3.gif" ALT="$^{-3}$"> respectively for nucleation, Aitken, and accumulation modes. In the second site (Kumpula, 6.3.2001-28.2.2003) they were 5500cm<IMG WIDTH="20" HEIGHT="18" ALIGN="BOTTOM" BORDER="0" src="acp-4-391-img3.gif" ALT="$^{-3}$">, 4000cm<IMG WIDTH="20" HEIGHT="18" ALIGN="BOTTOM" BORDER="0" src="acp-4-391-img3.gif" ALT="$^{-3}$">, and 1000cm<IMG WIDTH="20" HEIGHT="18" ALIGN="BOTTOM" BORDER="0" src="acp-4-391-img3.gif" ALT="$^{-3}$">. The total number concentration in nucleation and Aitken modes were usually significantly higher during workdays than during weekends. The temporal variations in the accumulation mode were less pronounced. The lower concentrations at Kumpula were mainly due to building construction and also the slight overall decreasing trend during these years. During the site changing a period of simultaneous measurements over two weeks were performed showing nice correlation at both sites.
Seasonal cycles of isoprene concentrations in the Amazonian rainforest

Tropical forests are an important global source of volatile organic compounds (VOCs) and other atmospheric trace gases. The high biodiversity in tropical rainforests complicates the extrapolation of biogenic volatile organic compound (BVOC) emissions from leaf-level measurements to landscape and regional or global scales. In Amazônia, a significant fraction of the carbon emitted from the biosphere to the atmosphere is emitted in the form of BVOCs, and the knowledge of these emissions is important to our understanding of tropical and global atmospheric chemistry and carbon cycling. As part of the Large scale Biosphere-atmosphere experiment in Amazônia (LBA). VOC concentrations were measured at two sites near Santarém, Para State, Brazil. The two sites are located in the National Forest of Tapajós, the first corresponding to primary forest and the second to a forest, that was selectively logged. The samples were collected simultaneously at heights of 65 and 55 m (20 and 10 m above forest canopy, respectively). The average isoprene mixing ratio was 2.2–2.5 ppb at the two sites and the standard deviations within a site ranged from 1 to 1.2 ppb. A strong seasonality of isoprene mixing ratio was observed and associated with the wet and dry seasons. The lowest mixing ratios were found during the transition between the wet to dry season, while at the start of the biomass burning season the mixing ratios increase. A qualitative analysis of a one dimensional model demonstrates that the seasonal cycle in concentrations reflects changes in isoprene production by the ecosystem, not changes in boundary layer dynamics or chemistry. The magnitude of the cycle indicates that the physiological capacity of the ecosystem to emit isoprene may depend on water availability although phenological changes could also contribute to the observed variations. A simple 1-D model that assumes mean daytime isoprene fluxes of 1.5 mg m−2h−1 and 0.9 mg m−2h−1 scaled by an algorithm depending on precipitation at the primary forest and selectively logged sites, respectively, is able to reproduce the observed vertical gradients.
Optimizing CO2 observing networks in the presence of model error: results from TransCom 3

We use a genetic algorithm to construct optimal observing networks of atmospheric concentration for inverse determination of net sources. Optimal networks are those that produce a minimum in average posterior uncertainty plus a term representing the divergence among source estimates for different transport models. The addition of this last term modifies the choice of observing sites, leading to larger networks than would be chosen under the traditional estimated variance metric. Model-model differences behave like sub-grid heterogeneity and optimal networks try to average over some of this. The optimization does not, however, necessarily reject apparently difficult sites to model. Although the results are so conditioned on the experimental set-up that the specific networks chosen are unlikely to be the best choices in the real world, the counter-intuitive behaviour of the optimization suggests the model error contribution should be taken into account when designing observing networks. Finally we compare the flux and total uncertainty estimates from the optimal network with those from the 3 control case. The  3 control case performs well under the chosen uncertainty metric and the flux estimates are close to those from the optimal case. Thus the 3 findings would have been similar if minimizing the total uncertainty guided their network choice.