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.
Nitrogen oxides are essential for the formation of secondary atmospheric aerosols and of atmospheric oxidants such as ozone and the hydroxyl radical, which controls the self-cleansing capacity of the ...atmosphere. Nitric acid, a major oxidation product of nitrogen oxides, has traditionally been considered to be a permanent sink of nitrogen oxides. However, model studies predict higher ratios of nitric acid to nitrogen oxides in the troposphere than are observed. A 'renoxification' process that recycles nitric acid into nitrogen oxides has been proposed to reconcile observations with model studies, but the mechanisms responsible for this process remain uncertain. Here we present data from an aircraft measurement campaign over the North Atlantic Ocean and find evidence for rapid recycling of nitric acid to nitrous acid and nitrogen oxides in the clean marine boundary layer via particulate nitrate photolysis. Laboratory experiments further demonstrate the photolysis of particulate nitrate collected on filters at a rate more than two orders of magnitude greater than that of gaseous nitric acid, with nitrous acid as the main product. Box model calculations based on the Master Chemical Mechanism suggest that particulate nitrate photolysis mainly sustains the observed levels of nitrous acid and nitrogen oxides at midday under typical marine boundary layer conditions. Given that oceans account for more than 70 per cent of Earth's surface, we propose that particulate nitrate photolysis could be a substantial tropospheric nitrogen oxide source. Recycling of nitrogen oxides in remote oceanic regions with minimal direct nitrogen oxide emissions could increase the formation of tropospheric oxidants and secondary atmospheric aerosols on a global scale.
H2SO4 formation from the reaction CH2OO + SO2 has been measured as a function of the water vapour concentration for close to atmospheric conditions. Second-order kinetics with regard to water ...indicates a preferred reaction of CH2OO with the water dimer. The obtained kinetic parameters lead to the conclusion that the atmospheric fate of CH2OO is dominated by the reaction with water vapour. A comparison with results from CH3CHOO and (CH3)2COO indicates a structure dependent reactivity of stabilized Criegee intermediates.
Here we report the measurement results of nitrous acid (HONO) and a suite of
relevant parameters on the NCAR C-130 research aircraft in the southeastern US
during the NOMADSS 2013 summer field study. ...The daytime HONO concentration
ranged from low parts per trillion by volume (pptv) in the free troposphere
(FT) to mostly within 5–15 pptv in the background planetary boundary layer
(PBL). There was no discernible vertical HONO gradient above the lower flight
altitude of 300 m in the PBL, and the transport of ground surface HONO was
not found to be a significant contributor to the tropospheric HONO budget. The
total in situ HONO source mean (±1 SD) was calculated as 53
(±21) pptv h−1 during the day. The upper-limit contribution from
NOx-related reactions was 10 (±5) pptv h−1, and the
contribution from photolysis of particulate nitrate (pNO3) was 38
(±23) pptv h−1, based on the measured pNO3 concentrations
and the median pNO3 photolysis rate constant of 2.0 × 10−4 s−1
determined in the laboratory using ambient aerosol samples. The
photolysis of HONO contributed to less than 10 % of the primary OH source.
However, a recycling NOx source via pNO3 photolysis was equivalent
to ∼ 2.3 × 10−6 mol m−2 h−1 in the air
column within the PBL, a considerable supplementary NOx source in the
low-NOx background area. Up to several tens of parts per trillion by volume of HONO were observed
in power plant and urban plumes during the day, mostly produced in situ
from precursors including NOx and pNO3. Finally, there was no
observable accumulation of HONO in the nocturnal residual layer and the
nocturnal FT in the background southeastern US, with an increase in the
HONO ∕ NOx ratio of ≤ 3 × 10−4 h−1 after sunset.
Direct Observations of Atmospheric Aerosol Nucleation Kulmala, Markku; Kontkanen, Jenni; Junninen, Heikki ...
Science (American Association for the Advancement of Science),
02/2013, Letnik:
339, Številka:
6122
Journal Article
Recenzirano
Atmospheric nucleation is the dominant source of aerosol particles in the global atmosphere and an important player in aerosol climatic effects. The key steps of this process occur in the ...sub—2-nanometer (nm) size range, in which direct size-segregated observations have not been possible until very recently. Here, we present detailed observations of atmospheric nanoparticles and clusters down to 1-nm mobility diameter. We identified three separate size regimes below 2-nm diameter that build up a physically, chemically, and dynamically consistent framework on atmospheric nucleation—more specifically, aerosol formation via neutral pathways. Our findings emphasize the important role of organic compounds in atmospheric aerosol formation, subsequent aerosol growth, radiative forcing and associated feedbacks between biogenic emissions, clouds, and climate.
Gas-phase low volatility organic compounds (LVOC), produced from oxidation of isoprene 4-hydroxy-3-hydroperoxide (4,3-ISOPOOH) under low-NO conditions, were observed during the FIXCIT chamber study. ...Decreases in LVOC directly correspond to appearance and growth in secondary organic aerosol (SOA) of consistent elemental composition, indicating that LVOC condense (at OA below 1 μg m–3). This represents the first simultaneous measurement of condensing low volatility species from isoprene oxidation in both the gas and particle phases. The SOA formation in this study is separate from previously described isoprene epoxydiol (IEPOX) uptake. Assigning all condensing LVOC signals to 4,3-ISOPOOH oxidation in the chamber study implies a wall-loss corrected non-IEPOX SOA mass yield of ∼4%. By contrast to monoterpene oxidation, in which extremely low volatility VOC (ELVOC) constitute the organic aerosol, in the isoprene system LVOC with saturation concentrations from 10–2 to 10 μg m–3 are the main constituents. These LVOC may be important for the growth of nanoparticles in environments with low OA concentrations. LVOC observed in the chamber were also observed in the atmosphere during SOAS-2013 in the Southeastern United States, with the expected diurnal cycle. This previously uncharacterized aerosol formation pathway could account for ∼5.0 Tg yr–1 of SOA production, or 3.3% of global SOA.
We use measurements made onboard the National Science Foundation’s C-130 research aircraft during the 2013 Nitrogen, Oxidants, Mercury, and Aerosol Distributions, Sources, and Sinks (NOMADSS) ...experiment to examine total Hg (THg) emission ratios (EmRs) for six coal-fired power plants (CFPPs) in the southeastern U.S. We compare observed enhancement ratios (ERs) with EmRs calculated using Hg emissions data from two inventories: the National Emissions Inventory (NEI) and the Toxics Release Inventory (TRI). For four CFPPs, our measured ERs are strongly correlated with EmRs based on the 2011 NEI (r 2 = 0.97), although the inventory data exhibit a −39% low bias. Our measurements agree best (to within ±32%) with the NEI Hg data when the latter were derived from on-site emissions measurements. Conversely, the NEI underestimates by approximately 1 order of magnitude the ERs we measured for one previously untested CFPP. Measured ERs are uncorrelated with values based on the 2013 TRI, which also tends to be biased low. Our results suggest that the Hg inventories can be improved by targeting CFPPs for which the NEI- and TRI-based EmRs have significant disagreements. We recommend that future versions of the Hg inventories should provide greater traceability and uncertainty estimates.
Reactive iodine plays a key role in determining the oxidation capacity, or cleansing capacity, of the atmosphere in addition to being implicated in the formation of new particles in the marine ...boundary layer. The postulation that heterogeneous cycling of reactive iodine on aerosols may significantly influence the lifetime of ozone in the troposphere not only remains poorly understood but also heretofore has never been observed or quantified in the field. Here, we report direct ambient observations of hypoiodous acid (HOI) and heterogeneous recycling of interhalogen product species (i.e., iodine monochloride ICl and iodine monobromide IBr) in a midlatitude coastal environment. Significant levels of ICl and IBr with mean daily maxima of 4.3 and 3.0 parts per trillion by volume (1-min average), respectively, have been observed throughout the campaign. We show that the heterogeneous reaction of HOI on marine aerosol and subsequent production of iodine interhalogens are much faster than previously thought. These results indicate that the fast formation of iodine interhalogens, together with their rapid photolysis, results in more efficient recycling of atomic iodine than currently considered in models. Photolysis of the observed ICl and IBr leads to a 32% increase in the daytime average of atomic iodine production rate, thereby enhancing the average daytime iodine-catalyzed ozone loss rate by 10 to 20%. Our findings provide direct field evidence that the autocatalytic mechanism of iodine release from marine aerosol is important in the atmosphere and can have significant impacts on atmospheric oxidation capacity.
Abstract
External cycling regenerating nitrogen oxides (NO
x
≡ NO + NO
2
) from their oxidative reservoir, NO
z
, is proposed to reshape the temporal–spatial distribution of NO
x
and consequently ...hydroxyl radical (OH), the most important oxidant in the atmosphere. Here we verify the in situ external cycling of NO
x
in various environments with nitrous acid (HONO) as an intermediate based on synthesized field evidence collected onboard aircraft platform at daytime. External cycling helps to reconcile stubborn underestimation on observed ratios of HONO/NO
2
and NO
2
/NO
z
by current chemical model schemes and rationalize atypical diurnal concentration profiles of HONO and NO
2
lacking noontime valleys specially observed in low-NO
x
atmospheres. Perturbation on the budget of HONO and NO
x
by external cycling is also found to increase as NO
x
concentration decreases. Consequently, model underestimation of OH observations by up to 41% in low NO
x
atmospheres is attributed to the omission of external cycling in models.
To better understand the role of aromatic hydrocarbons in new-particle formation, we measured the particle-phase abundance and volatility of oxidation products following the reaction of aromatic ...hydrocarbons with OH radicals. For this we used thermal desorption in an iodide-adduct Time-of-Flight Chemical-Ionization Mass Spectrometer equipped with a Filter Inlet for Gases and AEROsols (FIGAERO-ToF-CIMS). The particle-phase volatility measurements confirm that oxidation products of toluene and naphthalene can contribute to the initial growth of newly formed particles. Toluene-derived (C7) oxidation products have a similar volatility distribution to that of α-pinene-derived (C10) oxidation products, while naphthalene-derived (C10) oxidation products are much less volatile than those from toluene or α-pinene; they are thus stronger contributors to growth. Rapid progression through multiple generations of oxidation is more pronounced in toluene and naphthalene than in α-pinene, resulting in more oxidation but also favoring functional groups with much lower volatility per added oxygen atom, such as hydroxyl and carboxylic groups instead of hydroperoxide groups. Under conditions typical of polluted urban settings, naphthalene may well contribute to nucleation and the growth of the smallest particles, whereas the more abundant alkyl benzenes may overtake naphthalene once the particles have grown beyond the point where the Kelvin effect strongly influences the condensation driving force.
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