Oxidation products of monoterpenes and isoprene have a major influence on the global secondary organic aerosol (SOA) burden and the production of atmospheric nanoparticles and cloud condensation ...nuclei (CCN). Here, we investigate the formation of extremely low volatility organic compounds (ELVOC) from O ₃ and OH radical oxidation of several monoterpenes and isoprene in a series of laboratory experiments. We show that ELVOC from all precursors are formed within the first minute after the initial attack of an oxidant. We demonstrate that under atmospherically relevant concentrations, species with an endocyclic double bond efficiently produce ELVOC from ozonolysis, whereas the yields from OH radical-initiated reactions are smaller. If the double bond is exocyclic or the compound itself is acyclic, ozonolysis produces less ELVOC and the role of the OH radical-initiated ELVOC formation is increased. Isoprene oxidation produces marginal quantities of ELVOC regardless of the oxidant. Implementing our laboratory findings into a global modeling framework shows that biogenic SOA formation in general, and ELVOC in particular, play crucial roles in atmospheric CCN production. Monoterpene oxidation products enhance atmospheric new particle formation and growth in most continental regions, thereby increasing CCN concentrations, especially at high values of cloud supersaturation. Isoprene-derived SOA tends to suppress atmospheric new particle formation, yet it assists the growth of sub-CCN-size primary particles to CCN. Taking into account compound specific monoterpene emissions has a moderate effect on the modeled global CCN budget.
Significance Extremely low volatility organic compounds (ELVOC) are suggested to promote aerosol particle formation and cloud condensation nuclei (CCN) production in the atmosphere. We show that the capability of biogenic VOC (BVOC) to produce ELVOC depends strongly on their chemical structure and relative oxidant levels. BVOC with an endocyclic double bond, representative emissions from, e.g., boreal forests, efficiently produce ELVOC from ozonolysis. Compounds with exocyclic double bonds or acyclic compounds including isoprene, emission representative of the tropics, produce minor quantities of ELVOC, and the role of OH radical oxidation is relatively larger. Implementing these findings into a global modeling framework shows that detailed assessment of ELVOC production pathways is crucial for understanding biogenic secondary organic aerosol and atmospheric CCN formation.
Explaining the formation of secondary organic aerosol is an intriguing question in atmospheric sciences because of its importance for Earth's radiation budget and the associated effects on health and ...ecosystems. A breakthrough was recently achieved in the understanding of secondary organic aerosol formation from ozone reactions of biogenic emissions by the rapid formation of highly oxidized multifunctional organic compounds via autoxidation. However, the important daytime hydroxyl radical reactions have been considered to be less important in this process. Here we report measurements on the reaction of hydroxyl radicals with α- and β-pinene applying improved mass spectrometric methods. Our laboratory results prove that the formation of highly oxidized products from hydroxyl radical reactions proceeds with considerably higher yields than previously reported. Field measurements support these findings. Our results allow for a better description of the diurnal behaviour of the highly oxidized product formation and subsequent secondary organic aerosol formation in the atmosphere.
Sulfuric acid represents a fundamental precursor for new nanometre-sized atmospheric aerosol particles. These particles, after subsequent growth, may influence Earth´s radiative forcing directly, or ...indirectly through affecting the microphysical and radiative properties of clouds. Currently considered formation routes yielding sulfuric acid in the atmosphere are the gas-phase oxidation of SO
initiated by OH radicals and by Criegee intermediates, the latter being of little relevance. Here we report the observation of immediate sulfuric acid production from the OH reaction of emitted organic reduced-sulfur compounds, which was speculated about in the literature for decades. Key intermediates are the methylsulfonyl radical, CH
SO
, and, even more interestingly, its corresponding peroxy compound, CH
SO
OO. Results of modelling for pristine marine conditions show that oxidation of reduced-sulfur compounds could be responsible for up to ∼50% of formed gas-phase sulfuric acid in these areas. Our findings provide a more complete understanding of the atmospheric reduced-sulfur oxidation.
Measurements of the concentration and variability of ice
nucleating particles in the subtropical maritime boundary layer are reported.
Filter samples collected in Cabo Verde over the period 2009–2013 ...are
analyzed with a drop freezing experiment with sensitivity to
detect the few rare ice nuclei active at low supercooling. The data set is
augmented with continuous flow diffusion chamber measurements at temperatures
below −24 ∘C from a 2-month field campaign in Cabo Verde in 2016.
The data set is used to address the following questions: what are typical
concentrations of ice nucleating particles active at a certain temperature?
What affects their concentration and where are their sources? Concentration
of ice nucleating particles is found to increase exponentially by 7 orders of
magnitude from −5 to −38 ∘C. Sample-to-sample variation in the
steepness of the increase indicates that particles of different origin, with
different ice nucleation properties (size, composition), contribute to the
ice nuclei concentration at different temperatures. The concentration of ice
nuclei active at a specific temperature varies over a range of up to 4 orders
of magnitude. The frequency with which a certain ice nuclei concentration is
measured within this range is found to follow a lognormal
distribution, which can be explained by random dilution during transport. To
investigate the geographic origin of ice nuclei, source attribution of air
masses from dispersion modeling is used to classify the data into seven
typical conditions. While no source could be attributed to the ice nuclei
active at temperatures higher than −12 ∘C, concentrations at lower
temperatures tend to be elevated in air masses originating from the Sahara.
Gas‐phase oxidation routes of biogenic emissions, mainly isoprene and monoterpenes, in the atmosphere are still the subject of intensive research with special attention being paid to the formation of ...aerosol constituents. This laboratory study shows that the most abundant monoterpenes (limonene and α‐pinene) form highly oxidized RO2 radicals with up to 12 O atoms, along with related closed‐shell products, within a few seconds after the initial attack of ozone or OH radicals. The overall process, an intramolecular ROO→QOOH reaction and subsequent O2 addition generating a next R′OO radical, is similar to the well‐known autoxidation processes in the liquid phase (QOOH stands for a hydroperoxyalkyl radical). Field measurements show the relevance of this process to atmospheric chemistry. Thus, the well‐known reaction principle of autoxidation is also applicable to the atmospheric gas‐phase oxidation of hydrocarbons leading to extremely low‐volatility products which contribute to organic aerosol mass and hence influence the aerosol–cloud–climate system.
Not only in the solution phase: Highly oxidized RO2 radicals in the atmosphere are rapidly formed by autoxidation initiated by the reaction of O3 and OH radicals with biogenic emissions such as limonene and α‐pinene. Field measurements (see picture) confirm experimental findings from a flow‐tube study. The closed‐shell products from this process represent important aerosol constituents influencing aerosol–cloud–climate interactions.
Recent studies pointed to a high ice nucleating activity (INA) in the Arctic sea surface microlayer (SML). However, related chemical information is still sparse. In the present study, INA and free ...glucose concentrations were quantified in Arctic SML and bulk water samples from the marginal ice zone, the ice-free ocean, melt ponds, and open waters within the ice pack. T 50 (defining INA) ranged from −17.4 to −26.8 °C. Glucose concentrations varied from 0.6 to 51 μg/L with highest values in the SML from the marginal ice zone and melt ponds (median 16.3 and 13.5 μg/L) and lower values in the SML from the ice pack and the ice-free ocean (median 3.9 and 4.0 μg/L). Enrichment factors between the SML and the bulk ranged from 0.4 to 17. A positive correlation was observed between free glucose concentration and INA in Arctic water samples (T 50(°C) = (−25.6 ± 0.6) + (0.15 ± 0.04)·Glucose(μg/L), R P = 0.66, n = 74). Clustering water samples based on phytoplankton pigment composition resulted in robust but different correlations within the four clusters (R P between 0.67 and 0.96), indicating a strong link to phytoplankton-related processes. Since glucose did not show significant INA itself, free glucose may serve as a potential tracer for INA in Arctic water samples.
Atmospheric new-particle formation affects climate and is one of the least understood atmospheric aerosol processes. The complexity and variability of the atmosphere has hindered elucidation of the ...fundamental mechanism of new-particle formation from gaseous precursors. We show, in experiments performed with the CLOUD (Cosmics Leaving Outdoor Droplets) chamber at CERN, that sulfuric acid and oxidized organic vapors at atmospheric concentrations reproduce particle nucleation rates observed in the lower atmosphere. The experiments reveal a nucleation mechanism involving the formation of clusters containing sulfuric acid and oxidized organic molecules from the very first step. Inclusion of this mechanism in a global aerosol model yields a photochemically and biologically driven seasonal cycle of particle concentrations in the continental boundary layer, in good agreement with observations.
Atmospheric aerosols exert an important influence on climate through their effects on stratiform cloud albedo and lifetime and the invigoration of convective storms. Model calculations suggest that ...almost half of the global cloud condensation nuclei in the atmospheric boundary layer may originate from the nucleation of aerosols from trace condensable vapours, although the sensitivity of the number of cloud condensation nuclei to changes of nucleation rate may be small. Despite extensive research, fundamental questions remain about the nucleation rate of sulphuric acid particles and the mechanisms responsible, including the roles of galactic cosmic rays and other chemical species such as ammonia. Here we present the first results from the CLOUD experiment at CERN. We find that atmospherically relevant ammonia mixing ratios of 100 parts per trillion by volume, or less, increase the nucleation rate of sulphuric acid particles more than 100-1,000-fold. Time-resolved molecular measurements reveal that nucleation proceeds by a base-stabilization mechanism involving the stepwise accretion of ammonia molecules. Ions increase the nucleation rate by an additional factor of between two and more than ten at ground-level galactic-cosmic-ray intensities, provided that the nucleation rate lies below the limiting ion-pair production rate. We find that ion-induced binary nucleation of H(2)SO(4)-H(2)O can occur in the mid-troposphere but is negligible in the boundary layer. However, even with the large enhancements in rate due to ammonia and ions, atmospheric concentrations of ammonia and sulphuric acid are insufficient to account for observed boundary-layer nucleation.
Number
concentrations of ice-nucleating particles (NINP) in the Arctic
were derived from ground-based filter samples. Examined samples had been
collected in Alert (Nunavut, northern Canadian ...archipelago on Ellesmere
Island), Utqiaġvik, formerly known as Barrow (Alaska), Ny-Ålesund
(Svalbard), and at the Villum Research Station (VRS; northern Greenland). For
the former two stations, examined filters span a full yearly cycle. For VRS,
10 weekly samples, mostly from different months of one year, were included.
Samples from Ny-Ålesund were collected during the months from March until
September of one year. At all four stations, highest concentrations were
found in the summer months from roughly June to September. For those stations
with sufficient data coverage, an annual cycle can be seen. The spectra of
NINP observed at the highest temperatures, i.e., those obtained
for summer months, showed the presence of INPs that nucleate ice up to
−5 ∘C. Although the nature of these highly ice-active INPs could
not be determined in this study, it often has been described in the
literature that ice activity observed at such high temperatures originates
from the presence of ice-active material of biogenic origin. Spectra observed
at the lowest temperatures, i.e., those derived for winter months, were on
the lower end of the respective values from the literature on Arctic INPs or
INPs from midlatitude continental sites, to which a comparison is presented
herein. An analysis concerning the origin of INPs that were ice active at
high temperatures was carried out using back trajectories and satellite
information. Both terrestrial locations in the Arctic and the adjacent sea
were found to be possible source areas for highly active INPs.
Role of Sulfuric Acid in Atmospheric Nucleation Sipilä, Mikko; Berndt, Torsten; Petäjä, Tuukka ...
Science (American Association for the Advancement of Science),
03/2010, Letnik:
327, Številka:
5970
Journal Article
Recenzirano
Nucleation is a fundamental step in atmospheric new-particle formation. However, laboratory experiments on nucleation have systematically failed to demonstrate sulfuric acid particle formation rates ...as high as those necessary to account for ambient atmospheric concentrations, and the role of sulfuric acid in atmospheric nucleation has remained a mystery. Here, we report measurements of new particles (with diameters of approximately 1.5 nanometers) observed immediately after their formation at atmospherically relevant sulfuric acid concentrations. Furthermore, we show that correlations between measured nucleation rates and sulfuric acid concentrations suggest that freshly formed particles contain one to two sulfuric acid molecules, a number consistent with assumptions that are based on atmospheric observations. Incorporation of these findings into global models should improve the understanding of the impact of secondary particle formation on climate.
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