scholarly journals New particle formation in the volcanic eruption plume of the Piton de la Fournaise: specific features from a long-term dataset

2019 ◽  
Vol 19 (20) ◽  
pp. 13243-13265 ◽  
Author(s):  
Clémence Rose ◽  
Brice Foucart ◽  
David Picard ◽  
Aurélie Colomb ◽  
Jean-Marc Metzger ◽  
...  
Keyword(s):  
Significant Contribution ◽  
Total Concentration ◽  
Particle Formation ◽  
Volcanic Plume ◽  
New Particle Formation ◽  
Volcanic Origin ◽  
Piton De La Fournaise ◽  
Mixing Ratios ◽  
Primary Particles ◽  
Binary Nucleation

Abstract. New particle formation (NPF) is a key atmospheric process which may be responsible for a major fraction of the total aerosol number burden at the global scale, including in particular cloud condensation nuclei (CCN). NPF has been observed in various environments around the world, but some specific conditions, such as those encountered in volcanic plumes, remain poorly documented in the literature. Yet, understanding such natural processes is essential to better define pre-industrial conditions and their variability in climate model simulations. Here we report observations of NPF performed at the high-altitude observatory of Maïdo (2165 m a.s.l., La Réunion Island) between 1 January and 31 December 2015. During this time period, three effusive eruptions of the Piton de la Fournaise, located ∼39 km away from the station, were observed and documented, resulting in 29 d of measurement in volcanic plume conditions to be compared with 250 “non-plume days”. This dataset is, to our knowledge, the largest ever reported for the investigation of NPF in tropospheric volcanic plume conditions, and it allowed for the first time a statistical approach to characterize the process and also assessment of its relevance with respect to non-plume conditions. NPF was observed on 90 % of the plume days vs. 71 % of the non-plume days during the 4 months when the eruptions occurred. The events were on average detected earlier on plume days, most likely benefiting from larger amounts of precursors available at the site prior to nucleation hours. The overall effect of the plume conditions on the particle growth rate was limited. However, with the exception of September, particle formation rates were significantly higher on plume days. The signature of the volcanic plume on the aerosol spectra up to dp=600 nm was further investigated based on the analysis and fitting of the particle size distributions recorded under in-plume and off-plume conditions. The spectra recorded prior to nucleation hours, in the absence of freshly formed particles, featured a significant contribution of particles likely formed via heterogeneous processes at the vent of the volcano (and assimilated to volcanic primary particles) to the concentrations of the two accumulation modes on plume days. Later on in the morning, the concentrations of the nucleation and Aitken modes showed important variations on plume days compared to event days outside of plume conditions. The spectra recorded on event days, under in-plume and off-plume conditions, were further used to provide an average size distribution of the particles of volcanic origin, which clearly highlighted the dominant contribution of secondary over primary particles (93 %) to the total concentration measured on NPF event days within a volcanic plume. In a next step, particular attention was paid to the concentration of particles with dp>50 nm (N50), used as a proxy for potential CCN population. The contribution of secondary particles to the increase in N50 was the most frequent in plume conditions, and the magnitude of the increase was also more important on plume days compared to non-plume days. Finally, in order to further evaluate the effect of volcanic plume conditions on the occurrence of NPF, we analysed the variations of the condensation sink (CS) and [H2SO4], previously reported to play a key role in the process. Over the investigated months, higher CS (calculated prior to nucleation hours) were observed in plume conditions and coincided with high SO2 mixing ratios. Those most likely compensated for the strengthened loss rate of the vapours and favoured the occurrence of NPF, suggesting at the same time a key role of H2SO4 in the process. This last hypothesis was further supported by the correlation between the formation rate of 2 nm particles (J2) and [H2SO4], and by the fair approximation of J2 that was obtained by means of a recent parameterization of the binary nucleation of H2SO4–H2O. This last result demonstrates that in the absence of direct measurements of [H2SO4] and sub-3 nm particle concentrations, estimates of J2 could be fairly estimated from the knowledge of SO2 mixing ratios only. Finally, the use of the parameterization for ion-induced binary nucleation also highlighted the likely significant contribution of ion-induced nucleation for [H2SO4] below ∼8×108 cm−3.

scholarly journals New particle formation in the active volcanic plume of the Piton de la Fournaise: specific features from a long-term dataset

2019 ◽  
Author(s):  
Clémence Rose ◽  
Brice Foucart ◽  
David Picard ◽  
Aurélie Colomb ◽  
Jean-Marc Metzger ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Particle Formation ◽  
Volcanic Plume ◽  
New Particle Formation ◽  
Lower Altitude ◽  
Volcanic Origin ◽  
Piton De La Fournaise ◽  
Mixing Ratios ◽  
Primary Particles ◽  
The Mean

Abstract. New particle formation (NPF) is a key atmospheric process which may be responsible for a major fraction of the total aerosol number burden at the global scale, including in particular cloud condensation nuclei (CCN). NPF has been observed in various environments around the world, but some specific conditions, such as those encountered in volcanic plumes, remain poorly documented in the literature. Yet, understanding such natural processes is essential to better define preindustrial conditions in climate model simulations, as those form the baseline to calculate the radiative forcing caused by anthropogenic emissions. Here we report observations of NPF performed at the high-altitude observatory of Maïdo (2165 m a.s.l., La Réunion Island) between 1st January and 31st December 2015. During this time period, 3 effusive eruptions of the Piton de la Fournaise, located ~ 39 km away from the station, were observed and documented, resulting in 36 days of measurement in volcanic plume conditions to be compared with 250 non-plume days. This dataset is, to our knowledge, the largest ever reported for the investigation of NPF in tropospheric volcanic plume conditions, and allowed for the first time a statistical approach to characterize the process and also assess its relevance with respect to non-plume conditions. NPF was observed on 86 % of the plume days vs 71 % of the non-plume days during the 4 months when the eruptions occurred. The events were on average detected earlier on plume days, most likely benefiting from larger amounts of precursors available at the site prior to nucleation hours compared to non-plume days, during which condensable species were in contrast transported from lower altitude by the mean of convective processes. Surprisingly, the overall effect of the plume conditions on the particle growth rate was limited. However, with the exception of September, particle formation rates were significantly higher on plume days. The signature of the volcanic plume on the aerosol spectra up to dp = 600 nm was further investigated based on the analysis and fitting of the particle size distributions recorded in the different conditions. The spectra recorded prior to nucleation hours, in absence of freshly formed particles, featured a significant contribution of particles likely formed via heterogeneous processes at the vent of the volcano (and assimilated to volcanic primary particles) to the concentrations of the 2 accumulation modes on plume days. Later on in the morning, the concentrations of the nucleation and Aitken modes showed important variations on plume days compared to event days outside of plume conditions. The spectra recorded on event days, in and off-plume conditions, were further used to provide an average size distribution of the particles of volcanic origin, which clearly highlighted the dominant contribution of secondary over primary particles (96 %) to the total concentration measured on NPF event days within volcanic plume. In a next step, particular attention was paid to the concentration of particles with dp > 50 nm (N50), used as a proxy for potential CCN population. The contribution of secondary particles to the increase of N50 was the most frequent in plume conditions, and the magnitude of the increase was also more important on plume days compared to non-plume days. Last, in order to further evaluate the effect of volcanic plume conditions on the occurrence of NPF, we analysed the variations of the condensation sink (CS) and [H2SO4], previously reported to play a key role in the process. Over the investigated months, higher CS (calculated prior to nucleation hours) were observed in plume conditions, and coincided with high SO2 mixing ratios. Those most likely compensated for the strengthened loss rate of the vapour and favoured the occurrence of NPF, suggesting at the same time a key role of H2SO4 in the process. This last hypothesis was further supported by the correlation between the formation rate of 2 nm particles (J2) and [H2SO4], and by the fair approximation of J2 that was obtained by the mean of a recent parameterisation of the binary nucleation of H2SO4 – H2O. This last result was of high interest as it also demonstrated that in absence of direct measurement of [H2SO4] and sub-2nm particles concentration, estimates of J2 could be obtained from the knowledge of SO2 mixing ratios only.

Modelling new particle formation in a passive volcanic plume using a new parameterisation in WRF-Chem - effects on climate-relevant variables at the regional scale

2020 ◽  
Author(s):  
Céline Planche ◽  
Clémence Rose ◽  
Sandra Banson ◽  
Aurelia Lupascu ◽  
Mathieu Gouhier ◽  
...  
Keyword(s):  
Volcanic Eruption ◽  
Cluster Formation ◽  
Formation Rate ◽  
Regional Scale ◽  
Particle Formation ◽  
Volcanic Plume ◽  
New Particle Formation ◽  
Piton De La Fournaise ◽  
Volcanic Plumes ◽  
Eruption Plume

<p>New particle formation (NPF) is an important source of aerosol particles at  global scale, including, in particular, cloud condensation nuclei (CCN). NPF has been observed worldwide in a broad variety of environments, but some specific conditions, such as those encountered in volcanic plumes, remain poorly documented in the literature. Yet, these conditions could promote the occurrence of the process, as recently evidenced in the volcanic eruption plume of the Piton de la Fournaise (Rose at al. 2019); a dominant fraction of the volcanic particles was moreover found to be of secondary origin in the plume, further highlighting the importance of the particle formation and growth processes associated to the volcanic plume eruption. A deeper comprehension of such natural processes is thus essential to assess their climate-related effects at present days but also to better define pre-industrial conditions and their variability in climate model simulations.</p><p>Sulfuric acid (SA) is commonly accepted as one of the main precursors for atmospheric NPF, and its role could be even more important in volcanic plume conditions, as recently evidenced by the airborne measurements conducted in the passive volcanic plumes of Etna and Stromboli (Sahyoun et al., 2019). Indeed, the flights performed in the frame of the STRAP campaign have allowed direct measurement of SA in such conditions for the first time, and have highlighted a strong connection between the cluster formation rate and SA concentration. Following these observations, the objective of the present work was to further quantify the formation of new particles in a volcanic plume and assess the effects of the process at a regional scale. For that purpose, the new parameterisation of nucleation derived by Sahyoun et al. (2019) was introduced in the model WRF-Chem, further optimized for the description of NPF. The flight ETNA13 described in detail in Sahyoun et al. (2019) was used as a case study to evaluate the effect of the new parameterisation on the cluster formation rate and particle number concentration in various size ranges, including CCN (i.e. climate-relevant) sizes.</p><p><strong>References: </strong></p><p>Sahyoun, M., Freney, E., Brito, J., Duplissy, J., Gouhier, M., Colomb, A., Dupuy, R., Bourianne, T., Nowak, J. B., Yan, C., Petäjä, T., Kulmala, M., Schwarzenboeck, A., Planche, C., and Sellegri, K.: Evidence of new particle formation within Etna and Stromboli volcanic plumes and its parameterization from airborne in-situ measurements, J. Geophys. Res.-Atmos., 124, 5650–5668, https://doi.org/10.1029/2018JD028882, 2019.</p><p>Rose, C., Foucart, B., Picard, D., Colomb, A., Metzger, J.-M., Tulet, P., and Sellegri, K.: New particle formation in the volcanic eruption plume of the Piton de la Fournaise: specific features from a long-term dataset, Atmos. Chem. Phys., 19, 13243–13265, https://doi.org/10.5194/acp-19-13243-2019, 2019.</p>

scholarly journals Photochemical production of aerosols from real plant emissions

2009 ◽  
Vol 9 (13) ◽  
pp. 4387-4406 ◽  
Author(s):  
Th. F. Mentel ◽  
J. Wildt ◽  
A. Kiendler-Scharr ◽  
E. Kleist ◽  
R. Tillmann ◽  
...  
Keyword(s):  
Boreal Forests ◽  
Particle Formation ◽  
Reaction Chamber ◽  
System Level ◽  
Oh Radicals ◽  
New Particle Formation ◽  
Experimental Conditions ◽  
Mixing Ratios ◽  
Plant Emissions ◽  
Condensational Growth

Abstract. Emission of biogenic volatile organic compounds (VOC) which on oxidation form secondary organic aerosols (SOA) can couple the vegetation with the atmosphere and climate. Particle formation from tree emissions was investigated in a new setup: a plant chamber coupled to a reaction chamber for oxidizing the plant emissions and for forming SOA. Emissions from the boreal tree species birch, pine, and spruce were studied. In addition, α-pinene was used as reference compound. Under the employed experimental conditions, OH radicals were essential for inducing new particle formation, although O3 (≤80 ppb) was always present and a fraction of the monoterpenes and the sesquiterpenes reacted with ozone before OH was generated. Formation rates of 3 nm particles were linearly related to the VOC carbon mixing ratios, as were the maximum observed volume and the condensational growth rates. For all trees, the threshold of new particle formation was lower than for α-pinene. It was lowest for birch which emitted the largest fraction of oxygenated VOC (OVOC), suggesting that OVOC may play a role in the nucleation process. Incremental mass yields were ≈5% for pine, spruce and α-pinene, and ≈10% for birch. α-Pinene was a good model compound to describe the yield and the growth of SOA particles from coniferous emissions. The mass fractional yields agreed well with observations for boreal forests. Despite the somewhat enhanced VOC and OH concentrations our results may be up-scaled to eco-system level. Using the mass fractional yields observed for the tree emissions and weighting them with the abundance of the respective trees in boreal forests SOA mass concentration calculations agree within 6% with field observations. For a future VOC increase of 50% we predict a particle mass increase due to SOA of 19% assuming today's mass contribution of pre-existing aerosol and oxidant levels.

scholarly journals Photochemical production of aerosols from real plant emissions

2009 ◽  
Vol 9 (1) ◽  
pp. 3041-3094 ◽  
Author(s):  
Th. F. Mentel ◽  
J. Wildt ◽  
A. Kiendler-Scharr ◽  
E. Kleist ◽  
R. Tillmann ◽  
...  
Keyword(s):  
Boreal Forests ◽  
Particle Formation ◽  
Reaction Chamber ◽  
System Level ◽  
Oh Radicals ◽  
New Particle Formation ◽  
Experimental Conditions ◽  
Mixing Ratios ◽  
Plant Emissions ◽  
Condensational Growth

Abstract. By emission of volatile organic compounds (VOC) which on oxidation form secondary organic aerosols (SOA) the vegetation is coupled to atmosphere and climate. New particle formation from tree emissions was investigated in a new setup: a plant chamber coupled to a reaction chamber for oxidizing the plant emissions and for forming SOA. The boreal tree species birch, pine, and spruce were studied and α-pinene was used as reference compound. Under the experimental conditions OH radicals were essential for inducing new particle formation, although O3 (≤80 ppb) was always present and a part of the monoterpenes and the sesquiterpenes reacted already with ozone before OH was generated. Formation rates of 3 nm particles were linearly related to the carbon mixing ratios of the VOC, as were the maximum observed volume and the condensational growth rates. The threshold of new particle formation was lower for the tree emissions than for α-pinene. It was lowest for birch with the largest fraction of oxygenated VOC (OVOC) suggesting that OVOC may play a pivotal role in new particle formation. Incremental mass yields were ≈5% for pine, spruce and α-pinene, and ≈10% for birch. α-Pinene was a good model compound to describe the yield and the growth of SOA particles from coniferous emissions. The mass fractional yields agreed well with observations for boreal forests. Despite our somewhat enhanced VOC and OH concentrations our results may thus be up-scaled to eco-system level. Using the mass fractional yields observed for the tree emissions and weighting them with the abundance of the respective trees in boreal forests we calculate SOA mass concentrations which agree within 6% with field observations. For a future VOC increase of 50% we predict a particle mass increase due to SOA of 19% assuming today's mass contribution of pre-existing aerosol.

scholarly journals New particle formation inside ice clouds: In-situ observations in the tropical tropopause layer of the 2017 Asian Monsoon Anticyclone

2021 ◽  
Author(s):  
Ralf Weigel ◽  
Christoph Mahnke ◽  
Manuel Baumgartner ◽  
Martina Krämer ◽  
Peter Spichtinger ◽  
...  
Keyword(s):  
Ultrafine Particles ◽  
Asian Monsoon ◽  
Particle Formation ◽  
New Particle Formation ◽  
Mixing Ratios ◽  
Microphysical Properties ◽  
Tropical Tropopause ◽  
Ice Particles ◽  
Cloud Ice

Abstract. From 27 July to 10 August 2017 the airborne StratoClim mission took place in Kathmandu, Nepal where eight mission flights were conducted with the M-55 Geophysica up to altitudes of 20 km. New Particle Formation (NPF) was identified by the abundant presence of ultrafine aerosols, with particle diameters dp smaller than 15 nm, which were in-situ detected by means of condensation nuclei counting techniques. NPF fields in clear-skies as well as in the presence of cloud ice particles (dp > 3 µm) were encountered at upper troposphere/lowermost stratosphere (UT/LS) levels and within the Asian Monsoon Anticyclone (AMA). NPF-generated ultrafine particles in elevated concentrations (Nuf) were frequently found together with cloud ice (in number concentrations Nice of up to 3 cm−3) at heights between ~ 11 km and 16 km. From a total measurement time of ~ 22.5 hours above 10 km altitude, in-cloud NPF was in sum detected over ~ 1.3 hours (~ 50 % of all NPF records throughout StratoClim). Maximum Nuf of up to ~ 11000 cm−3 were detected coincidently with intermediate ice particle concentrations Nice of 0.05–0.1 cm−3 at comparatively moderate carbon monoxide (CO) contents of ~ 90–100 nmol mol−1. Neither under clear-sky nor during in-cloud NPF do the highest Nuf concentrations correlate with the highest CO mixing ratios, suggesting that an elevated pollutant load is not a prerequisite for NPF. Under clear-air conditions, NPF with elevated Nuf (> 8000 cm−3) occurred slightly less often than within clouds. In the presence of cloud ice, NPF with Nuf between 1500–4000 cm−3 were observed about twice as often as under clear air conditions. When ice water contents exceeded 1000 µmol mol−1 in very cold air ( 5000 mg−1) were rarely observed (~ 6 % of in-cloud NPF data). For specifying the constraining mechanisms for NPF possibly imposed by the microphysical properties of the cloud elements, the integral radius (IR) of the ice cloud population was identified as the most practicable indicator. Neither of both, the number of ice particles or the free distance between the ice particles, is clearly related to the NPF-rate detected. The results of a numerical simulation indicates how the IR affects the supersaturation of a condensable vapour, such as sulphuric acid, and that IR determines the effective limitation of NPF rates due to cloud ice.

scholarly journals <i>Fucus</i> and <i>Ascophyllum</i> seaweeds are significant contributors to coastal iodine emissions

2012 ◽  
Vol 12 (9) ◽  
pp. 25915-25939
Author(s):  
R.-J. Huang ◽  
U. R. Thorenz ◽  
M. Kundel ◽  
D. S. Venables ◽  
D. Ceburnis ◽  
...  
Keyword(s):  
Ambient Air ◽  
Exposure Period ◽  
Molecular Iodine ◽  
Particle Formation ◽  
Research Station ◽  
Emission Characteristics ◽  
Emission Rates ◽  
New Particle Formation ◽  
Initial Exposure ◽  
Mixing Ratios

Abstract. Based on the results of a pilot study in 2007, which found high mixing ratios of molecular iodine (I2) above the intertidal macroalgae (seaweed) beds at Mweenish Bay (Ireland), we extended the study to nine different locations in the vicinity of Mace Head Atmospheric Research Station on the west coast of Ireland during a field campaign in 2009. I2 mixing ratios from 104 to 393 ppt were found above the macroalgae beds, implying a high source strength of I2. Such mixing ratios are sufficient to result in photochemically-driven coastal new-particle formation events. Mixing ratios above the Ascophyllum nodosum and Fucus vesiculosus beds increased with exposure time – after 6 h exposure to ambient air the mixing ratios were one order of magnitude higher than those initially present. This contrasts with the emission characteristics of Laminaria digitata, where most I2 was emitted within the first half hour of exposure. Discrete in situ measurements (off-line) of I2 emission from ambient air-exposed chamber experiments of L. digitata, A. nodosum and F. vesiculosus substantially supported the field observations. Further online and time-resolved measurements of the I2 emission from O3-exposed macroalgal experiments in chamber confirmed the distinct I2 emission characteristics of A. nodosum and F. vesiculosus compared to that of L. digitata. The emission rates of A. nodosum and F. vesiculosus were comparable to or even higher than L. digitata after the initial exposure period of ~20–30 min. We suggest that A. nodosum and F. vesiculosus may provide an unaccounted and important source of photolabile iodine in the coastal boundary layer and that their impact on photochemistry and coastal new particle formation should be reevaluated in light of their longer exposure at low-tide and their widespread distribution.

scholarly journals The contribution of boundary layer nucleation events to total particle concentrations on regional and global scales

2006 ◽  
Vol 6 (12) ◽  
pp. 5631-5648 ◽  
Author(s):  
D. V. Spracklen ◽  
K. S. Carslaw ◽  
M. Kulmala ◽  
V.-M. Kerminen ◽  
G. W. Mann ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Sulfuric Acid ◽  
Particle Number ◽  
Formation Rate ◽  
Particle Surface ◽  
Particle Formation ◽  
New Particle Formation ◽  
Particle Surface Area ◽  
Primary Particles ◽  
Total Particle

Abstract. The contribution of boundary layer (BL) nucleation events to total particle concentrations on the global scale has been studied by including a new particle formation mechanism in a global aerosol microphysics model. The mechanism is based on an analysis of extensive observations of particle formation in the BL at a continental surface site. It assumes that molecular clusters form at a rate proportional to the gaseous sulfuric acid concentration to the power of 1. The formation rate of 3 nm diameter observable particles is controlled by the cluster formation rate and the existing particle surface area, which acts to scavenge condensable gases and clusters during growth. Modelled sulfuric acid vapour concentrations, particle formation rates, growth rates, coagulation loss rates, peak particle concentrations, and the daily timing of events in the global model agree well with observations made during a 22-day period of March 2003 at the SMEAR II station in Hyytiälä, Finland. The nucleation bursts produce total particle concentrations (>3 nm diameter) often exceeding 104 cm−3, which are sustained for a period of several hours around local midday. The predicted global distribution of particle formation events broadly agrees with what is expected from available observations. Over relatively clean remote continental locations formation events can sustain mean total particle concentrations up to a factor of 8 greater than those resulting from anthropogenic sources of primary organic and black carbon particles. However, in polluted continental regions anthropogenic primary particles dominate particle number and formation events lead to smaller enhancements of up to a factor of 2. Our results therefore suggest that particle concentrations in remote continental regions are dominated by nucleated particles while concentrations in polluted continental regions are dominated by primary particles. The effect of BL particle formation over tropical regions and the Amazon is negligible. These first global particle formation simulations reveal some interesting sensitivities. We show, for example, that significant reductions in primary particle emissions may lead to an increase in total particle concentration because of the coupling between particle surface area and the rate of new particle formation. This result suggests that changes in emissions may have a complicated effect on global and regional aerosol properties. Overall, our results show that new particle formation is a significant component of the aerosol particle number budget.

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

2018 ◽  
Author(s):  
Cristina Carnerero ◽  
Noemí Pérez ◽  
Cristina Reche ◽  
Marina Ealo ◽  
Gloria Titos ◽  
...  
Keyword(s):  
Mixed Layer ◽  
Growth Rates ◽  
Ultrafine Particles ◽  
Total Concentration ◽  
Particle Formation ◽  
Horizontal Distribution ◽  
New Particle Formation ◽  
Vehicle Exhaust ◽  
Radiative Balance ◽  
The Impact

Abstract. 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 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, in a field campaign in July 2016. 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 in the urban stations, which could be related to aircraft emissions transported from the airport. Considering all simultaneous diurnal NPF events registered, growth rates were significantly lower at the urban stations, ranging 2.0–3.9 nm h−1, compared to the suburban station (2.9–10.0 nm h−1). Total concentration of 9.1–25 nm particles reached 2.8 x 104 cm−3 at the urban station and 1.7 x 104 cm−3 at the suburban station, the mean daily values being 3.7 x 104 cm−3 (2.2 x 104 cm−3 at the suburban station) during event days. The formation rates of 9–25 nm particles peaked around noon and recorded a median value of 2.0 cm−3 s−1 and 1.1 cm−3 s−1 at the urban and suburban stations, respectively. The condensation and coagulation sinks presented minimum values shortly before sunrise, increasing after dawn reaching the maximum value at 14:00 UTC, with average daily mean values of 3.4 x 10−3 s−1 (2.5 x 10−3 s−1 at the suburban station) and 2.4 x 10−5 s−1, respectively, during event days. The vertical soundings demonstrated that ultrafine particles (UFP) are transported from surface levels to higher levels, thus newly-formed particles ascend from surface to the top of the mixing layer. 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 in the other stations considered in this study. This indicates that NPF occurs quasi-homogenously in an area spanning at least 17 km horizontally. The NPF events extend over the full vertical extension of the mixed layer reaching as high as 3000 m. This can have consequences in the radiative balance of the atmosphere and affect the climate. Results also evidenced that total particle concentration in and around Madrid in summer is dominated by NPF during summer, thus it may obscure the impact of vehicle exhaust emissions on levels of UFP.

scholarly journals The contribution of boundary layer nucleation events to total particle concentrations on regional and global scales

2006 ◽  
Vol 6 (4) ◽  
pp. 7323-7368 ◽  
Author(s):  
D. V. Spracklen ◽  
K. S. Carslaw ◽  
M. Kulmala ◽  
V.-M. Kerminen ◽  
G. W. Mann ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Particle Number ◽  
Marine Boundary Layer ◽  
Formation Rate ◽  
Particle Surface ◽  
Particle Formation ◽  
New Particle Formation ◽  
Particle Surface Area ◽  
Primary Particles ◽  
Total Particle

Abstract. The contribution of boundary layer nucleation events to total particle concentrations on the global scale has been studied by including a new particle formation mechanism in a global aerosol microphysics model. The mechanism is based on an analysis of extensive observations of particle formation in the boundary layer at a continental surface site. It assumes that molecular clusters form at a rate proportional to the gaseous sulfuric acid concentration to the power of 1. The formation rate of 3 nm diameter observable particles is controlled by the cluster formation rate and the existing particle surface area, which acts to scavenge condensable gases and clusters during growth. Modelled sulfuric acid vapour concentrations, particle formation rates, growth rates, coagulation loss rates, peak particle concentrations, and the daily timing of events in the global model agree well with observations made during a 22-day period of March 2003 at the SMEAR II station in Hyytiälä, Finland. The nucleation bursts produce total particle concentrations (>3 nm diameter) often exceeding 104 cm−3, which are sustained for a period of several hours around local midday. The predicted global distribution of particle formation events broadly agrees with what is expected from available observations. Over relatively clean remote continental locations formation events can sustain mean total particle concentrations up to a factor of 8 greater than those resulting from anthropogenic sources of primary organic and black carbon particles. However, in polluted continental regions anthropogenic primary particles dominate particle number and formation events lead to smaller enhancements of up to a factor of 2. Our results therefore suggest that particle concentrations in remote continental are dominated by nucleated particles while concentrations in polluted continental regions are dominated by primary particles. The effect of boundary layer particle formation over tropical regions and the Amazon is negligible. Particle concentrations are enhanced by a factor 3–10 over the remote Southern Ocean (30–70° S), resulting in total concentrations of ~250–1000 cm−3, in good agreement with observations. Particle formation tends to peak towards the top of the marine boundary layer and there is a lack of obvious burst-like behaviour at the sea surface. This result suggests that new particle formation in the marine boundary layer could be confused with entrainment from the free troposphere. These first global particle formation simulations reveal some interesting sensitivities. We show, for example, that significant reductions in primary particle emissions may lead to an increase in total particle concentration because of the coupling between particle surface area and the rate of new particle formation. This result suggests that changes in emissions may have a complicated effect on global and regional aerosol properties. Overall, our results show that new particle formation is a significant component of the aerosol particle number budget.

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