Parameterization of ion-induced nucleation rates based on ambient observations

Atmospheric ions participate in the formation of new atmospheric aerosol particles, yet their exact role in this process has remained unclear. Here we derive a new simple parameterization for ion-induced nucleation or, more precisely, for the formation rate of charged 2-nm particles. The parameterization is semi-empirical in the sense that it is based on comprehensive results of one-year-long atmospheric cluster and particle measurements in the size range ~1–42 nm within the EUCAARI (European Integrated project on Aerosol Cloud Climate and Air Quality interactions) project. Data from 12 field sites across Europe measured with different types of air ion and cluster mobility spectrometers were used in our analysis, with more in-depth analysis made using data from four stations with concomitant sulphuric acid measurements. The parameterization is given in two slightly different forms: a more accurate one that requires information on sulfuric acid and nucleating organic vapor concentrations, and a simpler one in which this information is replaced with the global radiation intensity. These new parameterizations are applicable to all large-scale atmospheric models containing size-resolved aerosol microphysics, and a scheme to calculate concentrations of sulphuric acid, condensing organic vapours and cluster ions

Future vegetation–climate interactions in Eastern Siberia: an assessment of the competing effects of CO2 and secondary organic aerosols

Disproportional warming in the northern high latitudes, and large carbon stocks in boreal and (sub)arctic ecosystems have raised concerns as to whether substantial positive climate feedbacks from biogeochemical process responses should be expected. Such feedbacks occur if increasing temperatures lead to e.g. a net release of CO2 or CH4. However, temperature-enhanced emissions of biogenic volatile organic compounds (BVOC) have been shown to contribute to the growth of secondary organic aerosol (SOA) which is known to have a negative radiative climate effect. Combining measurements in Eastern Siberia with model-based estimates of vegetation and permafrost dynamics, BVOC emissions and aerosol growth, we assess here possible future changes in ecosystem CO2 balance and BVOC-SOA interactions, and discuss these changes in terms of possible climate effects. On global level, both are very small but when concentrating on Siberia and the northern hemisphere the negative forcing from changed aerosol direct and indirect effects become notable – even though the associated temperature response would not necessarily follow a similar spatial pattern. While our analysis does not include other important processes that are of relevance for the climate system, the CO2 and BVOC-SOA interplay used serves as an example of the complexity of the interactions between emissions and vegetation dynamics that underlie individual terrestrial feedbacks and highlights the importance of addressing ecosystem-climate feedbacks in consistent, process-based model frameworks

Estimating the atmospheric concentration of Criegee intermediates and their possible interference in a FAGE-LIF instrument

We analysed the extensive dataset from the HUMPPA-COPEC 2010 and the HOPE 2012 field campaigns in the boreal forest and rural environments of Finland and Germany, respectively, and estimated the abundance of stabilised Criegee intermediates (SCIs) in the lower troposphere. Based on laboratory tests, we propose that the background OH signal observed in our IPI-LIF-FAGE instrument during the aforementioned campaigns is caused at least partially by SCIs. This hypothesis is based on observed correlations with temperature and with concentrations of unsaturated volatile organic compounds and ozone. Just like SCIs, the background OH concentration can be removed through the addition of sulfur dioxide. SCIs also add to the previously underestimated production rate of sulfuric acid. An average estimate of the SCI concentration of ∼ 5.0 x 104 molecules cm−3 (with an order of magnitude uncertainty) is calculated for the two environments. This implies a very low ambient concentration of SCIs, though, over the boreal forest, significant for the conversion of SO2 into H2SO4. The large uncertainties in these calculations, owing to the many unknowns in the chemistry of Criegee intermediates, emphasise the need to better understand these processes and their potential effect on the self-cleaning capacity of the atmosphere

Aerosol Particle Number Emissions and Size Distributions: Implementation in the GAINS Model and Initial Results

Particulate matter affects our health and climate. In addition to well based knowledge on the adverse health effects related to particle mass concentrations, there is increasing evidence showing that the number concentrations of ultra-fine aerosol particles, with diameters below 0.1 um, have negative health impacts, which are significantly different from those caused by larger particles with sizes over 1 um. Particles with diameters between 0.1 and 1 um can also be activated as cloud droplets; thereby, higher number concentrations can increase the cloud albedo and thus the proportion of solar radiation reflected back to space, causing a cooling aerosol climate effect. In addition to this indirect effect, aerosol particles affect Earth radiation budget directly by either scattering solar radiation (e.g. sulphate aerosol, cooling effect) or absorbing it (black carbon aerosol, warming effect). Currently, European air quality legislation on particulate matter is mainly focussing on particle mass, although emission standards for particle numbers have been introduced for mobile sources. Mass concentration is dominated by particles larger than 0.1 um, and it is not well associated with number concentration, due to the often different formation mechanisms of ultra-fine and larger particles. For combustion sources, some emission control technologies affect mainly large particle emissions, and may even increase emissions of ultra-fine particles. Hence, in order to comprehensively estimate health and climate effects of anthropogenic aerosol particles, it is necessary to quantify their emissions with both mass and number based metrics, including information on their size distribution. Currently, European air quality legislation on particulate matter is mainly focussing on particle mass, although emission standards for particle numbers have been introduced for mobile sources. Mass concentration is dominated by particles larger than 0.1 um, and it is not well associated with number concentration, due to the often different formation mechanisms of ultra-fine and larger particles. For combustion sources, some emission control technologies affect mainly large particle emissions, and may even increase emissions of ultra-fine particles. Hence, in order to comprehensively estimate health and climate effects of anthropogenic aerosol particles, it is necessary to quantify their emissions with both mass and number based metrics, including information on their size distribution. This report describes the implementation of size segregated particle number emission calculations in the GAINS model. Results show that in 2010 in Europe more than 60% of particle number emissions emerge from road transport, even though their share in total PM1 mass emissions (i.e., the mass of emitted particles with diameters below 1 um) is only 12%. Particle number emissions from road transport are expected to decrease rapidly in the future due to further tightening of exhaust emission legislation (EURO-standards). Due to the envisaged more pronounced particle number emission reduction in the road transport sector compared to the currently second and third largest source sectors, shipping and combustion of fuel wood and coal in the residential sector, emissions from the latter two sectors are anticipated to exceed road transport emissions by 2025. Estimated shares in total European emissions in 2025 range, depending on the applied future scenario, from 35 to 41% for shipping, from 26 to 29% for residential combustion and from 17 to 21% for road transport. The presented initial results are, however, subject to significant uncertainties, primarily due to limited measurement data for several emission sources

The Sexual Use of a Social Networking Site: The Case of Pup Twitter

This article examines how Twitter has been adopted and used by a sexual subculture in distinct ways. Drawing on interviews with 26 gay and bisexual men based in the UK who identify as ‘pups’, it demonstrates how a kinky sexual subculture exists on a social networking site in new and innovative ways, adapting various elements of Twitter to form a unique subculture that I call ‘Pup Twitter’. Engaging with debates about social trends related to sexuality, as well as contemporary understandings of social networking sites, the study documents how this subcultural sexual community, while predating Twitter, has adopted online methods to enhance communication, engagement, and even visibility. The intersection of sexuality and social networking sites is an area ripe for further study, and this article develops empirical and conceptual ways to examine this issue in the future

Global anthropogenic particle number emissions and their size distributions

Aerosol particle number concentrations and size distributions affect our climate by determining the formation of cloud droplets and thus altering the cloud reflective properties. The aerosol-cloud interactions are one of the main uncertainties in estimating the future climate change. One of the weaknesses in current climate modelling is the description of number emissions and size distributions of particles. Here, we present the first global results of implementing particle number emission factors to GAINS emission scenario model and discuss the related uncertainties. The uncertainties for different source sectors vary significantly, causing a steep difference in total uncertainties in different parts of the world. The reason for these uncertainties is the scarcity of data on particle number size distributions for certain sources. The implemented particle number emission factors, however, are expected to be a significant improvement over previously applied particle number emissions estimates in climate modelling

Estimates of the organic aerosol volatility in a boreal forest using two independent methods

The volatility distribution of secondary organic aerosols that formed and had undergone aging - i. e., the particle mass fractions of semi-volatile, low-volatility and extremely low volatility organic compounds in the particle phase - was characterized in a boreal forest environment of Hyytiala, southern Finland. This was done by interpreting field measurements using a volatility tandem differential mobility analyzer (VTDMA) with a kinetic evaporation model. The field measurements were performed during April and May 2014. On average, 40% of the organics in particles were semi-volatile, 34% were low-volatility organics and 26% were extremely low volatility organics. The model was, however, very sensitive to the vaporization enthalpies assumed for the organics (Delta H-VAP). The best agreement between the observed and modeled temperature dependence of the evaporation was obtained when effective vaporization enthalpy values of 80 kJ mol(-1) were assumed. There are several potential reasons for the low effective enthalpy value, including molecular decomposition or dissociation that might occur in the particle phase upon heating, mixture effects and compound-dependent uncertainties in the mass accommodation coefficient. In addition to the VTDMA-based analysis, semi-volatile and low-volatility organic mass fractions were independently determined by applying positive matrix factorization (PMF) to high-resolution aerosol mass spectrometer (HR-AMS) data. The factor separation was based on the oxygenation levels of organics, specifically the relative abundance of mass ions at m/z 43 (f43) and m/z 44 (f44). The mass fractions of these two organic groups were compared against the VTDMA-based results. In general, the best agreement between the VTDMA results and the PMF-derived mass fractions of organics was obtained when Delta H-VAP D 80 kJ mol(-1) was set for all organic groups in the model, with a linear correlation coefficient of around 0.4. However, this still indicates that only about 16% (R-2)of the variation can be explained by the linear regression between the results from these two methods. The prospect of determining of extremely low volatility organic aerosols (ELVOAs) from AMS data using the PMF analysis should be assessed in future studies.Peer reviewe

Future vegetation-climate interactions in Eastern Siberia : an assessment of the competing effects of CO2 and secondary organic aerosols

Disproportional warming in the northern high latitudes and large carbon stocks in boreal and (sub)arctic ecosystems have raised concerns as to whether substantial positive climate feedbacks from biogeochemical process responses should be expected. Such feedbacks occur when increasing temperatures lead, for example, to a net release of CO2 or CH4. However, temperature-enhanced emissions of biogenic volatile organic compounds (BVOCs) have been shown to contribute to the growth of secondary organic aerosol (SOA), which is known to have a negative radiative climate effect. Combining measurements in Eastern Siberia with model-based estimates of vegetation and permafrost dynamics, BVOC emissions, and aerosol growth, we assess here possible future changes in ecosystem CO2 balance and BVOC-SOA interactions and discuss these changes in terms of possible climate effects. Globally, the effects of changes in Siberian ecosystem CO2 balance and SOA formation are small, but when concentrating on Siberia and the Northern Hemisphere the negative forcing from changed aerosol direct and indirect effects become notable - even though the associated temperature response would not necessarily follow a similar spatial pattern. While our analysis does not include other important processes that are of relevance for the climate system, the CO2 and BVOC-SOA interplay serves as an example for the complexity of the interactions between emissions and vegetation dynamics that underlie individual terrestrial processes and highlights the importance of addressing ecosystem-climate feedbacks in consistent, process-based model frameworks.Peer reviewe

Vertical and horizontal distribution of regional new particle formation events in Madrid

The vertical profile of new particle formation (NPF) events was studied by comparing the aerosol size number distributions measured aloft and at surface level in a suburban environment in Madrid, Spain, using airborne instruments. The horizontal distribution and regional impact of the NPF events was investigated with data from three urban, urban background, and suburban stations in the Madrid metropolitan area. Intensive regional NPF episodes followed by particle growth were simultaneously recorded at three stations in and around Madrid during a field campaign in July 2016. The urban stations presented larger formation rates compared to the suburban station. Condensation and coagulation sinks followed a similar evolution at all stations, with higher values at urban stations. However, the total number concentration of particles larger than 2.5 nm was lower at the urban station and peaked around noon, when black carbon (BC) levels are at a minimum. The vertical soundings demonstrated that ultrafine particles (UFPs) are formed exclusively inside the mixed layer. As convection becomes more effective and the mixed layer grows, UFPs are detected at higher levels. The morning soundings revealed the presence of a residual layer in the upper levels in which aged particles (nucleated and grown on previous days) prevail. The particles in this layer also grow in size, with growth rates significantly smaller than those inside the mixed layer. Under conditions with strong enough convection, the soundings revealed homogeneous number size distributions and growth rates at all altitudes, which follow the same evolution at the other stations considered in this study. This indicates that UFPs are detected quasi-homogenously in an area spanning at least 17 km horizontally. The NPF events extend over the full vertical extension of the mixed layer, which can reach as high as 3000 m in the area, according to previous studies. On some days a marked decline in particle size (shrinkage) was observed in the afternoon, associated with a change in air masses. Additionally, a few nocturnal nucleation-mode bursts were observed at the urban stations, for which further research is needed to elucidate their origin.Peer reviewe