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1.
Nature ; 565(7741): 587-593, 2019 01.
Artigo em Inglês | MEDLINE | ID: mdl-30700872

RESUMO

Secondary organic aerosol contributes to the atmospheric particle burden with implications for air quality and climate. Biogenic volatile organic compounds such as terpenoids emitted from plants are important secondary organic aerosol precursors with isoprene dominating the emissions of biogenic volatile organic compounds globally. However, the particle mass from isoprene oxidation is generally modest compared to that of other terpenoids. Here we show that isoprene, carbon monoxide and methane can each suppress the instantaneous mass and the overall mass yield derived from monoterpenes in mixtures of atmospheric vapours. We find that isoprene 'scavenges' hydroxyl radicals, preventing their reaction with monoterpenes, and the resulting isoprene peroxy radicals scavenge highly oxygenated monoterpene products. These effects reduce the yield of low-volatility products that would otherwise form secondary organic aerosol. Global model calculations indicate that oxidant and product scavenging can operate effectively in the real atmosphere. Thus highly reactive compounds (such as isoprene) that produce a modest amount of aerosol are not necessarily net producers of secondary organic particle mass and their oxidation in mixtures of atmospheric vapours can suppress both particle number and mass of secondary organic aerosol. We suggest that formation mechanisms of secondary organic aerosol in the atmosphere need to be considered more realistically, accounting for mechanistic interactions between the products of oxidizing precursor molecules (as is recognized to be necessary when modelling ozone production).

2.
Environ Sci Technol ; 52(17): 10134-10143, 2018 09 04.
Artigo em Inglês | MEDLINE | ID: mdl-30064212

RESUMO

Designs of "improved" stoves are introduced recently to benefit the solid fuel consumption of cooking activities in developing countries, but the uncertainties concerning the combustion processes and particulate emissions remain poorly characterized. To help understand this, combustion in three examples of "improved" African cookstoves was investigated in the laboratory. A typical European heating stove was included for comparison purpose. Detailed aerosol emissions were studied in real-time with an Aerosol Mass Spectrometer and Single Particle Soot Photometer, to explore interactions between black carbon (BC) and organic carbon aerosols, which were parametrized according to modified combustion efficiency (MCE), a common metric used within the atmospheric emission community. Greater than 50% of the total organic matter (OM) was found in BC-containing particles when MCE was >0.95 for dry oak and coal fuels, whereas at lower MCE, over 80% of the total OM for most of the fuels existed in particles without detectable BC. When the OM mass fraction of total particulate matter (PM1) > 0.9, the mass ratio of OM to refractory BC in BC-containing particles was about 2-3, but only ∼0.8 when OM mass fraction <0.9. These findings are not currently included in models and such information should be considered in the future emission scenarios.


Assuntos
Poluentes Atmosféricos , Aerossóis , Carvão Mineral , Material Particulado , Fuligem
7.
Nature ; 525(7568): 234-8, 2015 Sep 10.
Artigo em Inglês | MEDLINE | ID: mdl-26354482

RESUMO

The amount of ice present in clouds can affect cloud lifetime, precipitation and radiative properties. The formation of ice in clouds is facilitated by the presence of airborne ice-nucleating particles. Sea spray is one of the major global sources of atmospheric particles, but it is unclear to what extent these particles are capable of nucleating ice. Sea-spray aerosol contains large amounts of organic material that is ejected into the atmosphere during bubble bursting at the organically enriched sea-air interface or sea surface microlayer. Here we show that organic material in the sea surface microlayer nucleates ice under conditions relevant for mixed-phase cloud and high-altitude ice cloud formation. The ice-nucleating material is probably biogenic and less than approximately 0.2 micrometres in size. We find that exudates separated from cells of the marine diatom Thalassiosira pseudonana nucleate ice, and propose that organic material associated with phytoplankton cell exudates is a likely candidate for the observed ice-nucleating ability of the microlayer samples. Global model simulations of marine organic aerosol, in combination with our measurements, suggest that marine organic material may be an important source of ice-nucleating particles in remote marine environments such as the Southern Ocean, North Pacific Ocean and North Atlantic Ocean.


Assuntos
Atmosfera/química , Gelo , Aerossóis/síntese química , Aerossóis/química , Ar , Organismos Aquáticos/química , Regiões Árticas , Diatomáceas/química , Congelamento , Compostos Orgânicos/análise , Compostos Orgânicos/química , Fitoplâncton/química , Água do Mar/química
10.
Anal Chem ; 86(22): 11238-45, 2014 Nov 18.
Artigo em Inglês | MEDLINE | ID: mdl-25303110

RESUMO

Secondary organic aerosol (SOA) is a key uncertainty in quantifying the impact of humans on Earth's climate. SOA is a complex mixture of oxidized organic species, and a fundamental hurdle in determining its composition is the lack of authentic standards for comparison and quantification. Organic synthesis can be used to produce pure standards, but is limited to compounds for which there is a degree of confidence in the proposed structure and can be expensive and time-consuming. In this study, a flow reactor was developed to form SOA in sufficient quantities to be collected and pure compounds subsequently isolated from the mixture using semipreparative high performance liquid chromatography. The purity and yield of each isolated compound were obtained using proton nuclear magnetic resonance ((1)H NMR), whereas molecular formulas were confirmed by high resolution Fourier transform ion cyclotron mass spectrometry (FTICR-MS). The effectiveness of the methodology has been evaluated here by using α-pinene as the precursor because it is the monoterpene with the most well characterized SOA chemistry. Eleven individual α-pinene SOA compounds were produced from α-pinene oxidation experiments and used for quantitative analysis of SOA formed during chamber experiments carried out close to ambient conditions. These compounds represented 25% of the total SOA mass, a significant improvement in mass balance compared to previous studies. This relatively simple approach may be extended to produce other SOA components not available commercially to improve quantification of aerosol sources.

11.
Phys Chem Chem Phys ; 16(36): 19453-69, 2014 Sep 28.
Artigo em Inglês | MEDLINE | ID: mdl-25105180

RESUMO

Laboratory measurements of vapour pressures for atmospherically relevant compounds were collated and used to assess the accuracy of vapour pressure estimates generated by seven estimation methods and impacts on predicted secondary organic aerosol. Of the vapour pressure estimation methods that were applicable to all the test set compounds, the Lee-Kesler [Reid et al., The Properties of Gases and Liquids, 1987] method showed the lowest mean absolute error and the Nannoolal et al. [Nannoonal et al., Fluid Phase Equilib., 2008, 269, 117-133] method showed the lowest mean bias error (when both used normal boiling points estimated using the Nannoolal et al. [Nannoolal et al., Fluid Phase Equilib., 2004, 226, 45-63] method). The effect of varying vapour pressure estimation methods on secondary organic aerosol (SOA) mass loading and composition was investigated using an absorptive partitioning equilibrium model. The Myrdal and Yalkowsky [Myrdal and Yalkowsky, Ind. Eng. Chem. Res., 1997, 36, 2494-2499] vapour pressure estimation method using the Nannoolal et al. [Nannoolal et al., Fluid Phase Equilib., 2004, 226, 45-63] normal boiling point gave the most accurate estimation of SOA loading despite not being the most accurate for vapour pressures alone.

13.
J Phys Chem A ; 117(16): 3428-41, 2013 Apr 25.
Artigo em Inglês | MEDLINE | ID: mdl-23506155

RESUMO

In order to model the properties and chemical composition of secondary organic aerosol (SOA), estimated physical property data for many thousands of organic compounds are required. Seven methods for estimating liquid density are assessed against experimental data for a test set of 56 multifunctional organic compounds. The group contribution method of Schroeder coupled with the Rackett equation using critical properties by Nannoolal was found to give the best liquid density values for this test set. During this work some problems with the representation of certain groups (aromatic amines and phenols) within the critical property estimation methods were identified, highlighting the importance (and difficulties) of deriving the parameters of group contribution methods from good quality experimental data. A selection of the estimation methods are applied to the 2742 compounds of an atmospheric chemistry mechanism, which showed that they provided consistent liquid density values for compounds with such atmospherically important (but poorly studied) functional groups as hydroperoxide, peroxide, peroxyacid, and PAN. Estimated liquid density values are also presented for a selection of compounds predicted to be important in atmospheric SOA. Hygroscopic growth factor (a property expected to depend on liquid density) has been calculated for a wide range of particle compositions. A low sensitivity of the growth factor to liquid density was found, and a single density value of 1350 kg·m(-3) could be used for all multicomponent SOA in the calculation of growth factors for comparison with experimentally measured values in the laboratory or the field without incurring significant error.


Assuntos
Aerossóis/química , Poluentes Atmosféricos/química , Atmosfera/análise , Compostos Orgânicos Voláteis/química , Aminas/química , Modelos Químicos , Peróxidos/química , Transição de Fase , Fenóis/química , Água/química
14.
Faraday Discuss ; 165: 45-73, 2013.
Artigo em Inglês | MEDLINE | ID: mdl-24600996

RESUMO

Carbonyl oxides ("Criegee intermediates"), formed in the ozonolysis of alkenes, are key species in tropospheric oxidation of organic molecules and their decomposition provides a non-photolytic source of OH in the atmosphere (Johnson and Marston, Chem. Soc. Rev., 2008, 37, 699, Harrison et al, Sci, Total Environ., 2006, 360, 5, Gäb et al., Nature, 1985, 316, 535, ref. 1-3). Recently it was shown that small Criegee intermediates, C.I.'s, react far more rapidly with SO2 than typically represented in tropospheric models, (Welz, Science, 2012, 335, 204, ref. 4) which suggested that carbonyl oxides could have a substantial influence on the atmospheric oxidation of SO2. Oxidation of 502 is the main atmospheric source of sulphuric acid (H2SO4), which is a critical contributor to aerosol formation, although questions remain about the fundamental nucleation mechanism (Sipilä et al., Science, 2010, 327, 1243, Metzger et al., Proc. Natl. Acad. Sci. U. S. A., 2010 107, 6646, Kirkby et al., Nature, 2011, 476, 429, ref. 5-7). Non-absorbing atmospheric aerosols, by scattering incoming solar radiation and acting as cloud condensation nuclei, have a cooling effect on climate (Intergovernmental Panel on Climate Change (IPCC), Climate Change 2007: The Physical Science Basis, Cambridge University Press, 2007, ref. 8). Here we explore the effect of the Criegees on atmospheric chemistry, and demonstrate that ozonolysis of alkenes via the reaction of Criegee intermediates potentially has a large impact on atmospheric sulphuric acid concentrations and consequently the first steps in aerosol production. Reactions of Criegee intermediates with SO2 will compete with and in places dominate over the reaction of OH with SO2 (the only other known gas-phase source of H2SO4) in many areas of the Earth's surface. In the case that the products of Criegee intermediate reactions predominantly result in H2SO4 formation, modelled particle nucleation rates can be substantially increased by the improved experimentally obtained estimates of the rate coefficients of Criegee intermediate reactions. Using both regional and global scale modelling, we show that this enhancement is likely to be highly variable spatially with local hot-spots in e.g. urban outflows. This conclusion is however contingent on a number of remaining uncertainties in Criegee intermediate chemistry.


Assuntos
Aerossóis , Atmosfera , Ácidos Sulfúricos/análise , Oxirredução
15.
Faraday Discuss ; 165: 273-88, 2013.
Artigo em Inglês | MEDLINE | ID: mdl-24601007

RESUMO

A simple approach to calculate liquid-liquid phase separation has been developed based on the derivation of partitioning coefficients between multiple liquid phases and inclusion in a framework used to partition an arbitrary number of compounds between the vapour and particle phases in an atmospheric aerosol. The representation compares favourably with a more complex and expensive benchmark gas-particle thermodynamic model for simple well-constrained systems. The model has then been applied to consider liquid phase separation in multicomponent particles formed by the equilibration of organic products generated by a near-explicit model of VOC oxidation. Inclusion of phase separation decreases the predicted mass of condensed organic material by -10 to -50%, dependent on the concentration of semi-volatile components and ambient conditions in the model scenario. The current study considers only two liquid phases, but the framework can readily accommodate an arbitrary number, though this is beyond the scope of the current work. Uncertainty introduced by the omission of phase separation is far lower than existing uncertainties in pure component vapour pressures, where orders of magnitude differences in predicted mass are found, though the bias introduced when choosing a particular method for estimating the saturation vapour pressure will influence the magnitude of phase separation. The proposed technique is the first to be used to practically deal with the many hundreds or thousands of components present in the ambient atmospheric aerosol.


Assuntos
Aerossóis/química , Gases/química , Compostos Inorgânicos/química , Modelos Químicos , Compostos Orgânicos/química
16.
Environ Sci Technol ; 46(24): 13093-102, 2012 Dec 18.
Artigo em Inglês | MEDLINE | ID: mdl-23163290

RESUMO

Characteristic organic aerosol (OA) emission ratios (ERs) and normalized excess mixing ratios (NEMRs) for biomass burning (BB) events have been calculated from ambient measurements recorded during four field campaigns. Normalized OA mass concentrations measured using Aerodyne Research Inc. quadrupole aerosol mass spectrometers (Q-AMS) reveal a systematic variation in average values between different geographical regions. For each region, a consistent, characteristic ratio is seemingly established when measurements are collated from plumes of all ages and origins. However, there is evidence of strong regional and local-scale variability between separate measurement periods throughout the tropical, subtropical, and boreal environments studied. ERs close to source typically exceed NEMRs in the far-field, despite apparent compositional change and increasing oxidation with age. The absence of any significant downwind mass enhancement suggests no regional net source of secondary organic aerosol (SOA) from atmospheric aging of BB sources, in contrast with the substantial levels of net SOA formation associated with urban sources. A consistent trend of moderately reduced ΔOA/ΔCO ratios with aging indicates a small net loss of OA, likely as a result of the evaporation of organic material from initial fire emissions. Variability in ERs close to source is shown to substantially exceed the magnitude of any changes between fresh and aged OA, emphasizing the importance of fuel and combustion conditions in determining OA loadings from biomass burning.


Assuntos
Aerossóis/análise , Biomassa , Fogo , Compostos Orgânicos/análise , África Ocidental , Monóxido de Carbono/análise , Fatores de Tempo
17.
Environ Sci Technol ; 46(17): 9290-8, 2012 Sep 04.
Artigo em Inglês | MEDLINE | ID: mdl-22881450

RESUMO

This paper reports indoor secondary organic aerosol, SOA, composition based on the results from an improved model for indoor air chemistry. The model uses a detailed chemical mechanism that is near-explicit to describe the gas-phase degradation of relevant indoor VOC species. In addition, gas-to-particle partitioning is included for oxygenated products formed from the degradation of limonene, the most ubiquitous terpenoid species in the indoor environment. The detail inherent in the chemical mechanism permits the indoor SOA composition to be reported in greater detail than currently possible using experimental techniques. For typical indoor conditions in the suburban UK, SOA concentrations are ~1 µg m(-3) and dominated by nitrated material (~85%), with smaller contributions from peroxide (12%), carbonyl (3%), and acidic (1%) material. During cleaning activities, SOA concentrations can reach 20 µg m(-3) with the composition dominated by peroxide material (73%), with a smaller contribution from nitrated material (21%). The relative importance of these different moieties depends crucially (in order) on the outdoor concentration of O(3), the deposition rates employed and the scaling factor value applied to the partitioning coefficient. There are currently few studies that report observation of aerosol composition indoors, and most of these have been carried out under conditions that are not directly relevant. This study highlights the need to investigate SOA composition in real indoor environments. Further, there is a need to measure deposition rates for key indoor air species on relevant indoor surfaces and to reduce the uncertainties that still exist in gas-to-particle phase parametrization for both indoor and outdoor air chemistry models.


Assuntos
Aerossóis/análise , Poluentes Atmosféricos/análise , Poluição do Ar em Ambientes Fechados/análise , Nitratos/análise , Peróxidos/análise , Monitoramento Ambiental , Modelos Químicos
19.
Phys Chem Chem Phys ; 11(36): 8021-8, 2009 Sep 28.
Artigo em Inglês | MEDLINE | ID: mdl-19727509

RESUMO

The following study extends previous work on modelling multicomponent surface tensions and the impact they have on aerosol and climate modelling. Mixed dicarboxylic acid and ammonium sulfate solution surface tensions have been measured experimentally and were modelled using an additive, a semi-empirical and two thermodynamic methods. A thermodynamic method with parameters fitted to binary solution data reproduced experimental results most closely with average absolute deviation from the experimental data over all measurements of 2.6%, compared with 7.7% for the additive, 8.1% for the semi-empirical and 7.3% for the other thermodynamic method. The choice of surface tension modelling method can lead to differences of up to 50% in the critical saturation ratios of aerosol particles. When applied to a trimodal aerosol distribution this leads to a difference in dry diameter for activation of 30 to 40 nm. This is greater than the difference induced by changing inorganic to organic mass ratios (>10 nm).


Assuntos
Aerossóis/química , Atmosfera/química , Ácidos Dicarboxílicos/química , Compostos Inorgânicos/química , Material Particulado/química , Água/química , Tempo (Meteorologia) , Misturas Complexas/química , Previsões , Gases/química , Gases/isolamento & purificação , Modelos Químicos , Tamanho da Partícula , Soluções , Tensão Superficial , Temperatura
20.
J Phys Chem A ; 112(39): 9413-22, 2008 Oct 02.
Artigo em Inglês | MEDLINE | ID: mdl-18593140

RESUMO

Aerosol optical tweezers are used to simultaneously characterize and compare the hygroscopic properties of two aerosol droplets, one containing inorganic and organic solutes and the second, referred to as the control droplet, containing a single inorganic salt. The inorganic solute is either sodium chloride or ammonium sulfate and the organic component is glutaric acid. The time variation in the size of each droplet (3-7 microm in radius) is recorded with 1 s time resolution and with nanometre accuracy. The size of the control droplet is used to estimate the relative humidity with an accuracy of better than +/-0.09%. Thus, the Kohler curve of the multicomponent inorganic/organic droplet, which characterizes the variation in equilibrium droplet size with relative humidity, can be determined directly. The measurements presented here focus on high relative humidities, above 97%, in the limit of dilute solutes. The experimental data are compared with theoretical treatments that, while ignoring the interactions between the inorganic and organic components, are based upon accurate representations of the activity-concentration relationships of aqueous solutions of the individual salts. The organic component is treated by a parametrized fit to experimental data or by the UNIFAC model and the water activity of the equilibrium solution droplet is calculated using the approach suggested by Clegg, Seinfeld and Brimblecombe or the Zdanovskii-Stokes-Robinson approximation. It is shown that such an experimental strategy, comparing directly droplets of different composition, enables highly accurate measurements of the hygroscopic properties, allowing the theoretical treatments to be rigorously tested. Typical deviations of the experimental measurements from theoretical predictions are shown to be around 1% in equilibrium size, comparable to the variation between the theoretical frameworks considered.

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