Emissions of carbon tetrafluoride CF₄, NF₃ and CHF₃ in east Asia have been calculated using atmospheric measurements and an atmospheric transport model. We calculate emissions of CF₄ to be quite constant between the years 2008 and 2015 for both China and South Korea, with 2015 emissions calculated at 4.33 ± 2.65 Gg yr^-1 and 0.36 ± 0.11 Gg yr^-1, respectively. Emission estimates of NF₃ from South Korea could be made with relatively small uncertainty at 0.6 ± 0.07 Gg yr^-1 in 2015.

The development of eddy-covariance measurements of ecosystem CO₂ fluxes began a new era in the field studies of photosynthesis. The interpretation of the very variable CO₂ fluxes in evergreen forests has been problematic especially in seasonal transition times. We apply two theoretical needle-level equations and show they can predict photosynthetic CO₂ flux between the atmosphere and Scots pine forests. This has strong implications for the interpretation of the global change and boreal forests.

Objective analysis has been used to discriminate between the local- and synoptic-scale precipitations based on wind and pressure fields at 500 hPa. Aerosol is found to be linked with changes in the vertical structure of precipitation, depending on precipitation regimes. There has been some success in separating aerosol and meteorological influences on precipitation.

Arctic mixed-phase clouds are a critical component of the Arctic climate system because of their ability to influence the surface radiation budget. The radiative impact of an individual cloud is closely linked to the ability of the cloud to convert liquid drops to ice. In this paper, we show through an observational record that clouds present in polluted atmospheric conditions have lower amounts of ice than similar clouds found in clean conditions.

The ice nucleation ability of different soot particles in the cirrus and mixed-phase cloud temperature regime is presented. The impact of aerosol particle size, particle morphology, organic matter and hydrophilicity on ice nucleation is examined. We propose ice nucleation proceeds via a pore condensation freezing mechanism for soot particles with the necessary physicochemical properties that nucleated ice well below water saturation.

This paper investigates how the activity of the Sun affects the amount of nitric oxide (NO) in the upper atmosphere. If NO descends lower down in the atmosphere, it can destroy ozone. We analyze satellite measurements of NO to create a model that can simulate the amount of NO at any given time. This model can indeed simulate NO with reasonable accuracy and it can potentially be used as an input for a larger model of the atmosphere that attempts to explain how the Sun affects our atmosphere.

Large uncertainties remain in understanding the influence of atmospheric environmental conditions on secondary organic aerosol (SOA) formation, evolution and properties. In this article, the GECKO-A modelling tool has been used in a box model under various environmental conditions to (i) explore the sensitivity of SOA formation and properties to changes on physical and chemical conditions and (ii) develop a volatility-basis-set-type parameterization for air quality models.

Aging of transported Saharan dust in the Caribbean was observed by electron microscopy, yielding size, chemical composition and mixing state for each individual particle. Models were developed for assessing mixing relevant for the atmosphere. Particles become internally mixed with sulfate during transport and sea salt in the Caribbean boundary layer. The mixing increases deposition velocity and dust cloud activation, and thus may impact on radiative and cloud nucleating properties.

Simultaneous observations of PAA, PAN and H₂O₂ are used to provide insight into processes influencing the HO_x chemistry of the boreal forest, including two biomass-burning-impacted periods. A significant contribution from photolytic HO_x sources was included in a box model analysis to align model predictions with measurements. The model predicts high levels of organic peroxy radicals, also at night-time.

Atmospheric aerosol particles may undergo liquid–liquid phase separation (LLPS) when exposed to varying relative humidity, with an aqueous organic phase enclosing an aqueous inorganic phase below a threshold of relative humidity. Brown carbon (BrC) compounds will redistribute to the organic phase upon LLPS. We use numerical modeling to study the shortwave radiative impact of LLPS containing BrC and conclude that it is not significant for atmospheric aerosol.

It is shown that using measurement-derived volatile organic compound (VOC) and organic aerosol (OA) emissions in the GEM-MACH air quality model provides better overall predictions compared to using bottom-up emission inventories. This work was done to better constrain the fugitive organic emissions from the Athabasca oil sands region, which are a challenge to estimate with bottom-up emission approaches. We use observations from the 2013 Joint Oil Sands Monitoring study.

Stratospheric polar processing diagnostics are compared in both hemispheres for four recent high-resolution reanalyses. Temperature-based diagnostics show largest differences before 1999 in the Antarctic; agreement becomes much better thereafter, when the reanalysis inputs include higher-resolution satellite radiances. Recommendations for usage of reanalysis data in research studies are given based on the differences among the reanalyses, which can be substantial and difficult to interpret.

Large-scale joint emission control measures were carried out in the Yangtze River Delta during the Hangzhou G20 Summit in 2016. The extent of secondary inorganic aerosol formation was found to be significantly enhanced under transport conditions from northern China. However, the formation of secondary organic aerosols was also greatly suppressed due to the emission control measures. Overall, it was found that regional/long-range transport could have offset part of the emission control efforts.

Under the effects of the Tibetan Plateau, dry low-pressure systems are often formed at 700 hPa in the Sichuan Basin, China, during winter. Here, we found that the activities of these dry low-pressure systems have significant influence on most winter heavy air pollution events in the Sichuan Basin. Influencing mechanisms have been summarized. The strong inversion layer above the atmospheric boundary layer induced by the low-pressure system plays a key role in the formation of heavy air pollution.

Uncertainty in the natural tropospheric sulfur cycle represents the largest source of uncertainty in radiative forcing estimates of sulfate aerosol. This study investigates the natural sulfur cycle in the marine troposphere using the GEOS-Chem model. We found that BrO is important for DMS oxidation and multiphase chemistry is important for MSA production and loss, which have implications for the yield of SO₂ and MSA from DMS oxidation and the radiative effect of DMS-derived sulfate aerosol.

PMCAMx-UF, a 3-D chemical transport model focusing on the simulation of ultrafine particles, has been extended with the addition of the volatility basis set (VBS) approach for the simulation of organic aerosol. The model was applied in Europe and its predictions were evaluated against field observations collected during the PEGASOS 2012 campaign. The condensation of organics led to an increase (50–120 %) in the larger particles but the total number concentration decreased by 10–30 %.

Focusing on Europe, this HTAP 2 study computes ozone in several global models when reducing anthropogenic emissions by 20 % in different world regions. The differences in model results are explored by use of a novel stepwise approach combining a tracer, CO and ozone. For ozone the contributions from the rest of the world are larger than from Europe, with the largest contributions from North America and eastern Asia. Contributions do, however, depend on the choice of ozone metric.

A global chemical transportation model (MOZART-4) was used to analyze the BC transport from the source regions and a radiative transfer model (SNICAR) was used to study the effect of BC on snow albedo on the northern Tibetan Plateau. The result provides useful information to study the effect of the upward BC emissions on environmental and climate issues. The radiative effect of BC deposition on the snow melting provides important information regarding the water resources in the region.

Surface roughness of ice crystals has recently been acknowledged to strongly influence the radiative properties of cold clouds such as cirrus, but it is unclear how this roughness arises. The study investigates the origins of ice surface roughness under a variety of atmospherically relevant conditions, using a novel method to measure roughness quantitatively. It is found that faster growth leads to stronger roughness. Roughness also increases following repeated growth–sublimation cycles.

Reanalyses (RAs) are models which assimilate observations and are widely used as proxies for the true atmospheric state. Here, we resample six leading RAs using the weighting functions of four high-res satellite instruments, allowing a like-for-like comparison. We find that the RAs generally reproduce the satellite data well, except at high altitudes and in the tropics. However, we also find that the RAs more tightly correlate with each other than with observations, even those they assimilate.

New particle formation involving sulfuric acid, bases and organic compounds is an important source of atmospheric aerosol particles. We investigate the capability of nano-Köhler theory to describe this process by simulating the dynamics of atmospheric molecular clusters. We find that nano-Köhler-type behavior occurs in our simulations when the saturation ratio of the organic vapor and the ratio between organic and inorganic vapor concentrations are in a suitable range.

The harvesting of crops emits large amounts of particles into the air. These particles can form and interact with clouds to alter cloud properties and precipitation, but the magnitude of these effects is unknown. This study looked at the ability of harvest particles to form ice in clouds by sampling with an ice nucleation chamber downwind of fields being harvested. Some crops emitted large amounts of ice-nucleating particles, and harvest emissions are mixtures of organics, soil, and minerals.

We describe the diversity and heterogeneity of urban CO₂ levels observed using the BErkeley Atmospheric CO₂ Observation Network, a distributed instrument of > 50 CO₂ sensors stationed every ~ 2 km across the San Francisco Bay Area. We demonstrate that relatively simple mathematical techniques, applied to these observations, can be used to detect the small changes in highway CO₂ emissions expected to result from upcoming fuel economy regulations, affirming the policy relevance of low-cost sensors.