We use one year (2012) of satellite imagery obtained from two NASA research satellites, Terra and Aqua, to detect linear contrail coverage and to estimate their physical properties over the Northern Hemisphere. The satellite-derived properties are compared with results collected from the same sensors in 2006 to estimate whether the impact of contrail coverage on climate has changed. The study is the first of its kind to measure contrail properties over a near-global scale from satellite imagery.

The liquid water path (LWP) is the strongest control on cloud albedo, such that a small change in LWP can have a large radiative impact. By changing the droplet number concentration (N_d) aerosols may be able to change the LWP, but the sign and magnitude of the effect is unclear. This work uses satellite data to investigate the relationship between N_d and LWP at a global scale and in response to large aerosol perturbations, suggesting that a strong decrease in LWP at high N_d may be overestimated.

We have modelled biomass burning haze concentrations in Singapore between 2010 and 2015. The major contributing haze source regions at two monitoring stations located in the western and eastern part of Singapore, less than 30 km apart, show significant variation on seasonal and annual timescales, as well as between the stations. Our results show that haze concentrations in Singapore are driven by a combination of local and regional weather, climate, and the location of regional burning.

Snow and liquid cloud particles were measured during the StormVEx and IFRACS programs at Storm Peak Lab to better understand snow formation in wintertime mountain clouds. We found significant interactions between the ice and liquid phases of the cloud. A relationship between large droplet and small ice crystal concentrations suggested snow formation by droplet freezing. Blowing snow can bias surface measurements, but its effect was ambiguous, calling for further work on this issue.

The chemical transport model PMCAMx was extended to investigate the effects of partitioning and photochemical aging of biomass burning emissions on organic aerosol (OA) concentrations and was applied in Europe. During the summer, the contribution of biomass burning to total OA levels over continental Europe was 16 % and during winter 47 %. Intermediate volatility organic compounds are predicted to be important precursors of secondary OA from biomass burning.

A MAX-DOAS instrument was operated to derive tropospheric vertical profiles of NO₂, SO₂, HONO, HCHO, CHOCHO and aerosols in the central western North China Plain in May and June 2016. The MAX-DOAS results are verified by comparisons with a collocated Raman lidar, overpass aircraft measurements, a sun photometer and in situ measurements. The contributions of regional transports and local emissions to the pollutants are evaluated based on case studies and statistic analysis.

This experimental study investigates the influence of volcanic ash chemical composition, crystallinity, and mineralogy on its ability to promote freezing of supercooled water. The results indicate that crystals in ash play a key role in this process and suggest that feldspars and perhaps pyroxenes in ash may be highly ice-active. These findings contribute to improving understanding of the potential of ash emissions from different explosive eruptions to impact ice formation in the atmosphere.

The poor diagnostic of the O₃ issue over southwestern Europe prevents authorities from implementing effective mitigation plans. This work is a pioneer in identifying that imported O₃ is the largest input to the ground-level O₃ concentration in the Iberian Peninsula, which is largely explained by vertical mixing. This study also proves that anthropogenic emissions control the severe O₃ peaks during stagnant conditions. Ad hoc local actions should complement national/European strategies.

As compound are emitted into the atmosphere, they can undergo chemical reactions to produce secondary products. This paper investigates the relations of compounds' unique chemical characteristics to the processes that formed them from emissions in the atmosphere. A model is applied to help with this investigation. The complexity of the atmosphere, including mixing of air masses and variability in precursor reactivity, is taken into consideration, and results are presented.

We evaluate the performance of a suite of models in simulating the large-scale transport from the northern midlatitudes to the Arctic using a CO-like idealized tracer. We find a large multi-model spread of the Arctic concentration of this CO-like tracer that is well correlated with the differences in the location of the midlatitude jet as well as the northern Hadley Cell edge. Our results suggest the Hadley Cell is key and zonal-mean transport by surface meridional flow needs better constraint.

Fine-temporal-resolution turbulent heat fluxes at the plateau scale have significant importance for studying diurnal variation characteristics of atmospheric boundary and weather systems in the Tibetan Plateau (TP) and its surroundings. Time series of land surface heat fluxes with high temporal resolution over the entire TP were derived. The derived surface heat fluxes proved to be in good agreement with in situ measurements and were superior to GLDAS flux products.

We explore the morphologies of multicomponent nanoparticles through atomistic molecular dynamics simulations under atmospherically relevant conditions. Phase separation is predicted for almost all simulated nanoparticles either between organics and inorganics or between hydrophobic and hydrophilic constituents. Three main particle types were identified: organic islands at the surface, inorganic core-organic shell morphologies and complex structures with hydrophobic and hydrophilic domains.

Atmospheric aerosols, tiny airborne particles, have an important impact on climate. However, a lack of understanding of the chemistry of aerosols is one of the largest contributors to uncertainty in predictions of climate change. Measurements of aerosols were carried out in the Arctic at Eureka Station, Canada, to better understand what role aerosols play in this fragile environment. It is found that organic aerosols, possibly originating from marine emissions, are ubiquitous during summertime.

Our study, for the first time, presents measurements of aerosol chemical composition and physical characteristics across northern India in the pre-monsoon and monsoon seasons of 2016 using the FAAM BAe-146 UK research aircraft. Across northern India, an elevated aerosol layer dominated by sulfate aerosol exists that diminishes with monsoon arrival. The Indo-Gangetic Plain (IGP) boundary layer is dominated by organics, whereas outside the IGP sulfate dominates with increased scattering aerosol.

Clouds exert substantial impacts on the global radiation budget and hydrological cycle. We propose a new proxy for the observed low-level cloud amount (LCA), so-called ELF (estimated low-level cloud fraction), and we show that ELF achieves the unprecedented best performance in diagnosing spatiotemporal variations of the observed LCA. Our study can be used to evaluate the performance of GCMs, identify the source of inaccurate simulation of LCA, and better understand climate sensitivity.

Global characteristics and trends in the tropopause (the boundary between troposphere and stratosphere) over a 35-year period (1981–2015) are evaluated using both observations and models. The use of two coordinate systems reveals previously undiagnosed changes in the tropopause altitude within the tropics and extratropics and these results have important implications for studies of climate and atmospheric composition (especially that related to stratosphere–troposphere exchange).

New particle formation events are identified at three sites in southern England, including a roadside and urban background site within London and a rural regional background site. The conditions favouring new particle formation events are identified and compared between the sites. Although a higher degree of pollution presents a greater condensation sink, it appears to be largely compensated for by faster particle growth rates.

We demonstrate that transport model errors, one of the main contributors to the uncertainty in regional CO₂ inversions, can be represented by a small-size ensemble carefully calibrated with meteorological data. Our results also confirm transport model errors represent a significant fraction of the model–data mismatch in CO₂ mole fractions and hence in regional inverse CO₂ fluxes.

The formation of secondary organic aerosol (SOA) from the photooxidation of three monoalkylbenzenes (toluene, ethylbenzene, and n-propylbenzene) has been simulated using the SOA model under varying environments (temperature, humidity, sunlight, NO_x levels, electrolytic inorganic seed – acidity and water content, and aging). The model demonstrates that the effect of an electrolytic aqueous phase on SOA formation is more critical than that of NO_x levels under SO₂-rich polluted urban environments.

For a long time sea-salt particles were considered the only types of particles that drive sea-fog formation but recently iodine oxide particles released from kelp have been identified as a source. There are no previous field studies to provide a direct timeline link between molecular iodine release, particle formation and sea-fog formation. The present observations from Cork Harbour provide such a link. A stabilizing mechanism enhancing distribution of iodine in the troposphere is suggested.

We use radars at three wavelengths to study cloud properties. The full Doppler spectra (rather than calculated averages of the spectra) are compared for the radars. This allows us to estimate the size and number of ice particles within the cloud. By following the evolution of the ice particles, we observe a region where particles rapidly and consistently increase in size. The observations suggest that these large particles form through interlocking of branched arms of smaller ice particles.