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Parrish D.D.,National Oceanic and Atmospheric Administration | Law K.S.,University of Versailles | Staehelin J.,Universitatstrasse 16 | Derwent R.,Rdscientific | And 8 more authors.
Atmospheric Chemistry and Physics | Year: 2012

Changes in baseline (here understood as representative of continental to hemispheric scales) tropospheric O3 concentrations that have occurred at northern mid-latitudes over the past six decades are quantified from available measurement records with the goal of providing benchmarks to which retrospective model calculations of the global O3 distribution can be compared. Eleven data sets (ten ground-based and one airborne) including six European (beginning in the 1950's and before), three North American (beginning in 1984) and two Asian (beginning in 1991) are analyzed. When the full time periods of the data records are considered a consistent picture emerges; O3 has increased at all sites in all seasons at approximately 1% yr-1 relative to the site's 2000 yr mixing ratio in each season. For perspective, this rate of increase sustained from 1950 to 2000 corresponds to an approximate doubling. There is little if any evidence for statistically significant differences in average rates of increase among the sites, regardless of varying length of data records. At most sites (most definitively at the European sites) the rate of increase has slowed over the last decade (possibly longer), to the extent that at present O3 is decreasing at some sites in some seasons, particularly in summer. The average rate of increase before 2000 shows significant seasonal differences (1.08 ± 0.09, 0.89 ± 0.10, 0.85 ± 0.11 and 1.21 ± 0.12% yr-1 in spring, summer, autumn and winter, respectively, over North America and Europe). © 2012 Author(s). CC Attribution 3.0 License. Source


Parrish D.D.,National Oceanic and Atmospheric Administration | Law K.S.,University of Versailles | Staehelin J.,Universitatstrasse 16 | Derwent R.,Rdscientific | And 8 more authors.
Geophysical Research Letters | Year: 2013

At northern midlatitudes the abundance of tropospheric O3 has increased by a factor of approximately 2 since the 1950s. The cause of this increase is generally attributed to increasing anthropogenic precursor emissions, but present chemical and transport models cannot quantitatively reproduce its magnitude. Here we show another manifestation of changes in O 3 abundance - a shift of the seasonal cycle at northern midlatitudes so that the observed peak concentrations now appear earlier in the year than in previous decades. The rate of this shift has been 3 to 6 days per decade since the 1970s. We examine possible reasons to explain this shift and suggest it is due to changes in atmospheric transport patterns combined with spatial and temporal changes in emissions. Detailed modeling is necessary to test these hypotheses; this investigation will provide useful guidance for improving global chemistry-climate models and stringent tests of the model results. Key Points The date of the maximum of tropospheric ozone has moved to earlier in the year Change has been approximately constant at 3 to 6 days per decade since the 1970s Cause of change may be due to changing climate and/or anthropogenic emissions. ©2013. American Geophysical Union. All Rights Reserved. Source


Mikkonen S.,University of Eastern Finland | Romakkaniemi S.,U.S. National Center for Atmospheric Research | Smith J.N.,University of Eastern Finland | Smith J.N.,U.S. National Center for Atmospheric Research | And 18 more authors.
Atmospheric Chemistry and Physics | Year: 2011

Gaseous sulphuric acid is a key precursor for new particle formation in the atmosphere. Previous experimental studies have confirmed a strong correlation between the number concentrations of freshly formed particles and the ambient concentrations of sulphuric acid. This study evaluates a body of experimental gas phase sulphuric acid concentrations, as measured by Chemical Ionization Mass Spectrometry (CIMS) during six intensive measurement campaigns and one long-term observational period. The campaign datasets were measured in Hyytiälä, Finland, in 2003 and 2007, in San Pietro Capofiume, Italy, in 2009, in Melpitz, Germany, in 2008, in Atlanta, Georgia, USA, in 2002, and in Niwot Ridge, Colorado, USA, in 2007. The long term data were obtained in Hohenpeissenberg, Germany, during 1998 to 2000. The measured time series were used to construct proximity measures ("proxies") for sulphuric acid concentration by using statistical analysis methods. The objective of this study is to find a proxy for sulfuric acid that is valid in as many different atmospheric environments as possible. Our most accurate and universal formulation of the sulphuric acid concentration proxy uses global solar radiation, SO2 concentration, condensation sink and relative humidity as predictor variables, yielding a correlation measure (R) of 0.87 between observed concentration and the proxy predictions. Interestingly, the role of the condensation sink in the proxy was only minor, since similarly accurate proxies could be constructed with global solar radiation and SO2 concentration alone. This could be attributed to SO2 being an indicator for anthropogenic pollution, including particulate and gaseous emissions which represent sinks for the OH radical that, in turn, is needed for the formation of sulphuric acid. © 2011 Author(s). Source


Manninen H.E.,University of Helsinki | Nieminen T.,University of Helsinki | Asmi E.,Finnish Meteorological Institute | Gagne S.,University of Helsinki | And 46 more authors.
Atmospheric Chemistry and Physics | Year: 2010

We present comprehensive results on continuous atmospheric cluster and particle measurements in the size range ∼1-42 nm within the European Integrated project on Aerosol Cloud Climate and Air Quality interactions (EUCAARI) project. We focused on characterizing the spatial and temporal variation of new particle formation events and relevant particle formation parameters across Europe. Different types of air ion and cluster mobility spectrometers were deployed at 12 field sites across Europe from March 2008 to May 2009. The measurements were conducted in a wide variety of environments, including coastal and continental locations as well as sites at different altitudes (both in the boundary layer and the free troposphere). New particle formation events were detected at all of the 12 field sites during the year-long measurement period. From the data, nucleation and growth rates of newly formed particles were determined for each environment. In a case of parallel ion and neutral cluster measurements, we could also estimate the relative contribution of ion-induced and neutral nucleation to the total particle formation. The formation rates of charged particles at 2 nm accounted for 1-30% of the corresponding total particle formation rates. As a significant new result, we found out that the total particle formation rate varied much more between the different sites than the formation rate of charged particles. This work presents, so far, the most comprehensive effort to experimentally characterize nucleation and growth of atmospheric molecular clusters and nanoparticles at ground-based observation sites on a continental scale. © Author(s) 2010. Source


Paasonen P.,University of Helsinki | Paasonen P.,International Institute For Applied Systems Analysis | Olenius T.,University of Helsinki | Kupiainen O.,University of Helsinki | And 18 more authors.
Atmospheric Chemistry and Physics | Year: 2012

Sulphuric acid is a key component in atmospheric new particle formation. However, sulphuric acid alone does not form stable enough clusters to initiate particle formation in atmospheric conditions. Strong bases, such as amines, have been suggested to stabilize sulphuric acid clusters and thus participate in particle formation. We modelled the formation rate of clusters with two sulphuric acid and two amine molecules (J A2B2) at varying atmospherically relevant conditions with respect to concentrations of sulphuric acid ([H 2SO 4]), dimethylamine ([DMA]) and trimethylamine ([TMA]), temperature and relative humidity (RH). We also tested how the model results change if we assume that the clusters with two sulphuric acid and two amine molecules would act as seeds for heterogeneous nucleation of organic vapours (other than amines) with higher atmospheric concentrations than sulphuric acid. The modelled formation rates J A2B2 were functions of sulphuric acid concentration with close to quadratic dependence, which is in good agreement with atmospheric observations of the connection between the particle formation rate and sulphuric acid concentration. The coefficients K A2B2 connecting the cluster formation rate and sulphuric acid concentrations as J A2B2Combining double low line K A2B2[H 2SO 4]2 turned out to depend also on amine concentrations, temperature and relative humidity. We compared the modelled coefficients K A2B2 with the corresponding coefficients calculated from the atmospheric observations (K obs) from environments with varying temperatures and levels of anthropogenic influence. By taking into account the modelled behaviour of J A2B2 as a function of [H 2SO 4], temperature and RH, the atmospheric particle formation rate was reproduced more closely than with the traditional semi-empirical formulae based on sulphuric acid concentration only. The formation rates of clusters with two sulphuric acid and two amine molecules with different amine compositions (DMA or TMA or one of both) had different responses to varying meteorological conditions and concentrations of vapours participating in particle formation. The observed inverse proportionality of the coefficient K obs with RH and temperature agreed best with the modelled coefficient K A2B2 related to formation of a cluster with two H 2SO 4 and one or two TMA molecules, assuming that these clusters can grow in collisions with abundant organic vapour molecules. In case this assumption is valid, our results suggest that the formation rate of clusters with at least two of both sulphuric acid and amine molecules might be the rate-limiting step for atmospheric particle formation. More generally, our analysis elucidates the sensitivity of the atmospheric particle formation rate to meteorological variables and concentrations of vapours participating in particle formation (also other than H 2SO 4). © 2012 Author(s). Source

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