Optical properties of polar and non-polar extracts of biomass burning organic aerosols (BBOAs) generated by burning of globally and regionally important fuels were studied. The non-polar fraction of BBOAs was found to be more light absorbing than the polar fraction. Laboratory aging of BBOAs produced by flaming fuels increased aerosol light absorption attributed to the formation of organo-nitrogen compounds. Refractive indices were retrieved for both polar and non-polar extracts of BBOAs.

This paper first describes the new version 2 Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) polar stratospheric cloud (PSC) detection and composition classification algorithm. We then present a state-of-the-art PSC reference data record and climatology constructed by applying the v2 algorithm to the over 11 years CALIOP spaceborne lidar dataset spanning 2006–2017. This work is part of a larger effort being performed under the auspices of the SPARC Polar Stratospheric Cloud Initiative.

We model the evolution of several BBOA markers including levoglucosan during aging experiments conducted in an atmospheric Teflon chamber, in order to evaluate the influence of vapor wall loss on the determination of the rate constants of the compounds with hydroxyl radicals (OH).

Our main results demonstrate that atmospheric N_r pollution in eastern China is more serious in the northern region than in the southern region. Any effects of current emission controls are not yet apparent in N_r pollution. NH₃ emissions from fertilizer use were the largest contributor (36 %) to total inorganic N_r deposition. Our results provide useful information for policy-makers that mitigation of NH₃ emissions should be a priority to tackle serious N deposition.

The GEOS-5 atmospheric model provided forecasts for the Atmospheric Tomography Mission (ATom). GEOS-5 shows skill in simulating the carbon monoxide (CO) measured in ATom-1. African fires contribute to high CO over the tropical Atlantic, but non-fire sources are the main contributors elsewhere. ATom aims to provide a chemical climatology, so we consider whether ATom-1 occurred during a typical summer month. Satellite observations suggest ATom-1 occurred in a clean but not exceptional month.

Aerosol particles are a major public health concern, but particle properties contributing to their toxicity are not well known. Oxidising components such as peroxy acids might contribute significantly to particle toxicity. However, there is a lack of analytical methods for their characterisation. We synthesized three peroxy acids, developed an analysis method and showed that degradation affects peracid yield, likely leading to underestimation of their concentration in conventional analyses.

Our work establishes how surface tension reduction influences droplet growth and activation of simple sea spray mimics (NaCl coated with fatty acids). Fatty acids can substantially reduce droplet surface tension near activation but have limited impact on activation. Coating of NaCl by palmitic acid (a wax) impedes water uptake, but this impedance is removed if oleic acid (a liquid) is mixed in. The properties that surface-active compounds need to impact activation are theoretically examined.

Persistent organic pollutants that have accumulated in soils over decades can be remobilised by volatilisation. Clean air masses advected with the onset of the summer monsoon to India enhance revolatilisation of chemicals which have been banned for decades. During propagation of the monsoon northward across the subcontinent, the air is increasingly polluted by these secondary emissions. Remobilisation of some PCBs may even have reached a historical high, 40 years after peak emission.

We perform a model intercomparison of summertime high Arctic clouds. Observed concentrations of aerosol particles necessary for cloud formation fell to extremely low values, coincident with a transition from cloudy to nearly cloud-free conditions. Previous analyses have suggested that at these low concentrations, the radiative properties of the clouds are determined primarily by these particle concentrations. The model results strongly support this hypothesis.

Exhaust emissions from a light-duty diesel engine were introduced into an atmospheric simulation chamber which was used as a holding-cell for sampling, allowing instruments capable of providing detailed chemical speciation of exhaust gas emissions to be used. The effect of different engine conditions on the exhaust gas composition was investigated. The exhaust composition changed considerably due to two influencing factors, engine combustion and diesel oxidative catalyst efficiency.

We used measurements of CO₂ in the atmosphere from the GOSAT satellite and from surface sites around the world, together with a transport model and a unique estimation technique, to quantify CO₂ sources and removals over a recent period. We find that climate variations can strongly influence uptake by vegetation and release in decay and fires. However, regional gaps in observations and inaccuracies to which current satellite technology is susceptible result in important estimation biases.

Aerosol pH are often directly compared across studies while ignoring the inconsistency in standard states. This study attempts to address this issue by comparing aerosol pH with different standard states on the basis of theoretical considerations followed with a set of field data as an example. Application of a pH standardization protocol including a precise statement of thermodynamic model parameters is recommended to avoid biases in cross-comparison.

This study shows the observational evidence of the role of humidity and associations from wind shear and aerosol concentrations on the evolution of deep convective clouds from shallow clouds. This study shows how humidity, wind shear, and aerosols influence a parcel's buoyancy before the clouds form.

During 2006–2015 volcanism contributed 40 % of the stratospheric aerosol load. We compute the AOD (aerosol optical depth) of the stratosphere (from the tropopause to 35 km altitude) using new techniques of handling CALIOP data. Regional and global AODs are presented for the entire stratosphere in relation to transport patterns, and the AOD is presented for three stratospheric layers: the LMS, the potential temperature range of 380 to 470 K, and altitudes above the 470 K isentrope.

New particle formation (NPF) is a common occurrence in urban environments. Using a 500-day dataset obtained in Brisbane, Australia, we observed that NPF events occurred on 37 % of days and 10 % of nights. However, particle growth occurred on 70 % of nights. We show that when particles are measured by an instrument with a detection limit of 3 nm or above, particle growth events may be easily misidentified as NPF events. This can lead to an overestimation of the occurrence of NPF events.

Recent measurements of NO_x and HONO suggest that photolysis of particulate nitrate in sea-salt aerosols is important in terms of marine boundary layer oxidant chemistry. We present the first global-scale assessment of the significance of this new chemical pathway for NO_x, O₃, and OH in the marine boundary layer. We also present a preliminary assessment of the potential impact of photolysis of particulate nitrate associated with other aerosol types on continental boundary layer chemistry.

Ice cloud mass is assessed on a global scale using the latest satellite and reanalysis datasets. While ice cloud variability driven by large-scale circulations is an area of relative consensus, models and observations disagree strongly on the overall magnitude and finer-scale variability of atmospheric ice mass. The results reflect limitations of the current Earth observing system and indicate ice microphysical assumptions as the likely culprit of disagreement.

A coupled atmospheric dispersion modelling system has been developed, comprising a regional chemical transport model and a street-scale urban dispersion model. It was applied in London for 2012 and for all common regulated air quality pollutants, with evaluation against measurements. The modelling demonstrates the interaction between local and regional scales, which differs between pollutants. Real-world estimates of emissions have been used to adjust standard factors and improve model results.

We combine satellite-borne and ground-based observations to investigate the intra-annual variations of regional aerosol column loading, vertical distribution, and particle types. Column aerosol optical depth (AOD), as well as AOD > 800 m, peaks in summer/spring. However, AOD < 800 m and surface PM_2.5 concentrations mostly peak in winter. The aerosol intra-annual variations differ significantly according to aerosol types characterized by different sizes, light absorption, and emission sources.

We present the first piece of observational evidence of the increasing trend of fine nitrate aerosol in the North China Plain (NCP) during 2005–2015. The summertime nitrate formation mechanism is dissected with a multiphase chemical box model based on observations at three different sites. The nitrate formation is most sensitive to NO₂ and to a lesser extent to O₃. NH₃ plays a significant role in prompting the nitrate formation, but it is usually in excess in summer in the NCP region.

Stratospheric sudden warmings (SSWs) are natural major disruptions of the polar stratospheric circulation that also affect surface weather. In the literature there are conflicting claims as to whether SSWs will change in the future. The confusion comes from studies using different models and methods. Here we settle the question by analysing 12 models with a consistent methodology, to show that no robust changes in frequency and other features are expected over the 21st century.

This paper presents the first direct atmospheric observations of the formation and evolution of tar balls (TBs) in forest fires collected during the Department of Energy’s Biomass Burning Observation Project (BBOP). We quantify, for the first time, the TB mass fraction in the BB plumes and show that this mass fraction increases from less than 1 % to 50 % within the first couple of hours of plume aging. Using Mie theory we find that TBs are consistent with being weak light absorbers.

Mineral dust is the most abundant atmospheric aerosol component in terms of dry mass. In this study, we integrate recent aircraft measurements of dust microphysical and optical properties with satellite retrievals of aerosol and radiative fluxes to quantify the dust direct radiative effects on the shortwave and longwave radiation at both the top of the atmosphere and the surface in the tropical North Atlantic during summer months.

The 11-year solar cycle is an important driver of climate variability. Changes in incoming solar ultraviolet radiation affect atmospheric ozone, which in turn influences atmospheric temperatures. Constraining the impact of the solar cycle on ozone is therefore important for understanding climate variability. This study examines the representation of the solar influence on ozone in numerical models used to simulate past and future climate. We highlight important differences among model datasets.

The mixing state of black carbon is one of the key uncertainties limiting the ability of models to estimate the direct radiative effect. In this work, we present aircraft measurements from the Canadian Arctic of coating thickness as a function of black carbon core diameter and black-carbon-containing particle number fractions. We use these measurements to inform estimates of the direct radiative effect in Arctic aerosol simulations.

POA and SOA from seven heated cooking oil emissions were investigated in a smog chamber. We found that PMF analysis separated POA and SOA better than the residual spectrum method and the traditional method, assuming first-order POA loss. The PMF factors mass spectra were compared with those of ambient PMF factors. Our results suggest that COA source analysis from ambient data is likely complicated by the cooking style and atmospheric oxidation conditions.

This paper examines an event in May 2016 when smoke from forest fires in Canada reached the UK at altitudes between 3 and 11 km above the surface. Although events of this kind are fairly common in the summer months, this one was unusual because it persisted for 9 days due to a stationary flow pattern that kept the smoky air from travelling away to the east. A network of lidars and ceilometers around the UK provided round-the-clock observations of the smoke event.

Using AATSR ADV (1995–2011) and MODIS C6.1 (2000–2017) annual and seasonal aerosol optical depth (AOD) aggregates, we obtained information regarding the occurrence of aerosols and their spatial and temporal variation over China. We specifically focused on regional differences in annual and seasonal AOD behavior for selected regions. AOD dataset comparisons, validation results and AOD tendencies during the overlapping period (2000–2011) are discussed.

The impact of photooxidation of 2-methyl-3-butene-2-ol (MBO) on the concentration of radical species was studied in the atmospheric simulation chamber SAPHIR. MBO is a volatile organic compound mainly emitted by ponderosa and lodgepole pines which are very abundant in forests in the central-west USA. A very good agreement between measured and modelled radical concentrations and products from the oxidation of MBO was observed in an environment with NO of ~ 200 pptv.

In this study, we investigated the potential impact on clouds and climate by organic particles emitted from the ocean surface, using a global climate model. These particles have previously been found to promote ice crystal formation, which may alter the properties of clouds. Our study, however, found a weak global impact by these particles, which brings into question their relative importance and points to the need for further verification with other models and at more regional scales.

By integrating several modeling methods, we find considerable contributions of foreign anthropogenic emissions to surface ozone over China (2–11 ppb). For anthropogenic ozone over China, the foreign contribution is 40–50 % below 2 km and 85 % in the upper troposphere. For total foreign anthropogenic ozone over China, the portion of transboundary ozone produced within foreign emission source regions is less than 50 %, with the rest produced by precursors transported out of those source regions.

We present measurements from a field study conducted in an agriculturally intensive region in the southeastern US during the fall of 2016 to investigate how NH₃ affects particle acidity and SOA formation via gas–particle partitioning of semi-volatile organic acids. For this study, higher NH₃ concentrations relative to what has been measured in the region in previous studies had minor effects on PM₁ organic acids and their influence on the overall organic aerosol and PM₁ mass concentrations.

Rapid industrialization, traffic growth and urbanization resulted in a significant increase in the tropospheric trace gases over Asia. There is global concern about rising levels of these trace gases. The monsoon convection transports these gases to the upper-level-anticyclone. In this study, we show transport of these gases to the extratropics via eddy-shedding from the anticyclone. We also deliberate on changes in ozone heating rates due to the transport of Asian trace gases.

Snow albedo plays a key role in the Earth and climate system. It can be affected by impurities and snow properties. This study implements new parameterizations into a widely used snow model to account for effects of snow shape and black carbon–snow mixing state on snow albedo reduction in the Tibetan Plateau. This study points toward an imperative need for extensive measurements and improved model characterization of snow grain shape and aerosol–snow mixing state in Tibet and elsewhere.

By applying an updated version of WRF-Chem, we aim to investigate the full effects of dust, including direct, semi-direct, and indirect effects, on the regional weather system over East Asia during a dust-intensive period. This is the first study to document the full effects of dust during a typical dust-intensive period over East Asia by applying an online coupled regional numerical model.

Molecular identities and abundances of organic compounds residing in the gas and particle phases above a Finnish boreal forest are presented. We determined that in each phase, the organic components are categorized into three subgroups based on their behavior in time. Some are more enhanced at night, others during midday, and another around sunrise. Identifying such collective behavior can potentially connect the chemical processes that evolve in time to specific distributions of products.