The paper aims at understanding the variability of nitric acid (HNO₃) in the stratosphere; 9-year time series of IASI measurements are analysed and, for the first time for HNO₃, fitted with regression models in order to identify the factors at play. It was found that the annual variability is the main driver and that the polar stratospheric clouds influence greatly HNO₃ variability at polar latitudes. The results show the potential of such analyses to better understand the polar processes.

The deep convection in tropics can inject cloud ice into tropical tropopause layer (TTL), which moistens and increases water vapor there. We primarily study the spatial distribution of impacts from several physical processes on TTL water vapor from observations and trajectory model simulations. The analysis shows the potential moistening impact from evaporation of cloud ice on TTL water vapor. A chemistry–climate model is used to confirm the impact from evaporation of convective ice.

The optical thickness and particle effective radius of a cirrus above liquid water clouds and a DCC topped by an anvil cirrus are retrieved based on SMART and MODIS radiance measurements. For the cirrus, retrieved particle effective radius are validated with corresponding in situ data using a vertical weighting method. This approach allows to assess the measurements, retrieval algorithms, and derived cloud products.

The combined analysis of stratospheric methane and water vapour data derived from SCIAMACHY solar occultation measurements shows the expected anti-correlation and a clear temporal variation related to waves in equatorial zonal winds. Above about 20 km most of the additional water vapour is attributed to the oxidation of methane. The SCIAMACHY data confirm that at lower altitudes water vapour and methane are transported from the tropics to higher latitudes.

The Arctic climate is changing much faster than other regions on Earth. Hence, it is necessary to investigate the processes that are liable for this phenomena and to document the current situation in the Arctic. Therefore, we measured the number and also the size of aerosol particles. It turned out that we captured the transition from the Arctic spring to the Arctic summer and that the according air masses show differences in particle properties. Also, the particles have a low water receptivity.

The main hypothesis of this paper is that people who live in large cities in the UK disobey the smoke control law as it has not been actively enforced for decades now. However, the use of wood in residential heating has increased, partly due to renewable energy targets, but also for discretionary (i.e. pleasant fireplaces) reasons. Our study is based mainly in London, but similar struggles with urban air quality due to residential wood and coal burning are seen in other major European cities.

Crystal nucleation in polar stratospheric clouds (PSCs) has a direct impact on stratospheric chemistry and ozone. However, the mechanism of nucleation has been unclear for decades, limiting prediction of the response of ozone to atmospheric changes. We experimentally demonstrate that meteoric material can trigger nucleation heterogeneously and this can produce observed crystal concentrations in PSCs. This discovery paves the way to robust modelling of past and future trends in PSCs and ozone.

The urban aerosol particles in central Budapest consist of two externally mixed classes – nearly hydrophobic and less volatile particles, which were assigned to vehicle emissions (large mass fractions of soot likely coated with water-insoluble organic compounds) – and of less hygroscopic and volatile particles (moderately transformed aged combustion particles composed of partly oxygenated organics and inorganic salts internally mixed).

We used observations of HCHO formaldehyde columns from the OMI satellite instrument and the GEOS-Chem atmospheric chemistry model to investigate how and why HCHO varies over India. We find that emissions of biogenic VOC from forests are the most powerful driver, with forests' response to seasonal temperature variations causing variation over time. Human-driven emissions of VOC and burning of vegetation have detectable, but more limited, impacts.

This research is the first study concerning the 1-year online monitoring of volatile organic compounds in an oil–gas field in China. The VOC concentrations, compositions and ozone formation potential in this study are quite different from other research. The contributions of natural gas and the other four sources to total VOCs are quantified. The different timescale variations in different sources are described. This research broadens our knowledge of VOC behavior in this type of region.

The impact of El Niño in the lower stratosphere is nonlinear in spring. While moderate El Niño events lead to cooling in this region, strong El Niño events appear to lead to warming, and hence the water vapor response is nonlinear too. The net effect is that strong El Nino events, such as in 1997/1998 and 2015/2016, lead to qualitatively different water vapor impacts as compared to moderate El Nino events.

Highly time and chemically resolved submicron aerosol properties were characterized online for the first time in a high-altitude site (Qomolangma station, 4276 m a.s.l.) in the northern Himalayas by using the Aerodyne HR-ToF-AMS. Biomass burning plumes were frequently observed and the dynamic processes (emissions, transport, and chemical processing) were characterized. The source and chemical composition of organic aerosol were further elucidated using positive matrix factorization analysis.

Black carbon (BC) aerosol in the Tibetan Plateau (TP) has important effects on the regional climate and hydrological processes in South and East Asia. We characterized BC at a high-altitude remote site in the southeastern Tibetan Plateau using a single-particle soot photometer and a photoacoustic extinctiometer. Our study provides insight into the sources and evolution of BC aerosol on the TP, and the results will be useful for improving models of the radiative effects in this area.

We evaluate the representation of tropical convection regimes in atmospheric climate models with satellite-based observations from GPS radio occultation. We find that models have large temperature biases in the tropopause region. In moist convection regions, models underestimate moisture up to 40 % over oceans whereas in dry regions they overestimate it by 100 %. Our findings show that RO observations are a valuable data source for the evaluation and development of next generation climate models.

Native to Australasia, the remarkable adaptability, rapid growth rates and high quality wood of eucalypt trees has led to them the most widely planted hardwood forest trees in the world. In contrast to boreal and tropical forests, there has been little study of aerosol formation in these regions. Here, we study the secondary organic aerosol formation from the very fast reaction of α-phellandrene, emitted from eucalypts, and identify key products and reaction pathways.

This study aims at proposing a method to better assess the initial magma fragmentation produced during explosive volcanic eruptions. We worked on merging field, radar, and satellite data to estimate the total grain-size distribution, which is used within simulations to reconstruct the tephra loading and far-travelling airborne ash dispersal. This approach is applied to 23 November 2013, giving the very fine ash fraction related to volcanic hazards (e.g. air traffic safety).

A novel method for classifying Arctic precipitation using ground based remote sensors is presented. The classification reveals two distinct, primary regimes of precipitation over the central Greenland Ice Sheet: snowfall coupled to deep, fully glaciated ice clouds or to shallow, mixed-phase clouds. The ice clouds are associated with low-pressure storm systems from the southeast, while the mixed-phase clouds slowly propagate from the southwest along a quiescent flow.

In China, the haze pollution in December has become increasingly serious over recent decades. The relationship between the snow cover and the December haze days was analyzed. This relationship significantly strengthened after the mid-1990s, which is attributed to the effective connections between the snow cover and the Eurasian atmospheric circulations.

Carbon dioxide emissions and uptake were estimated for Cape Town, South Africa. We placed two high-precision analysers in lighthouses located on either end of Cape Town (Robben Island and Hangklip). The Cape Point GAW station provided background measurements. We were able to improve the agreement between modelled and observed concentrations, relative to initial estimates provided. This methodology could potentially be scaled up to provide monitoring and verification of city emissions.

The aim of this study is to find the origin of mesospheric stationary planetary wave (SPW) in the subtropics and in mid and polar latitudes in mid winter 2015/2016. Our results based on observations show that upward propagating SPW and in situ generated SPWs by longitudinally variable gravity wave drag and by instabilities can be responsible for the occurrence of mesospheric SPWs and that they can act at the same time, which confirms earlier model studies.

California's greenhouse gas reduction programs will require adoption of low-carbon energy sources across all economic sectors. We selected the least-cost portfolio of new energy sources using an energy–economic model. We then specified new air pollution emissions and simulated air quality with 4 km spatial resolution across the entire state. We find that the adoption of low-carbon energy reduced air pollution deaths 24–26 %, providing USD 11.4–20.4 billion per year of economic benefits.

The aerosol particle number size distributions (PNSDs) measured in one urban background site (Milan) and in one rural mountainous site (Oga San Colombano) have been studied and compared. Detailed statistical analyses have shown that a common empirical PNSD pattern exists, except for the urban winter data. In order to explain this phenomenon, we analysed the aerosol dynamics by considering the influence of primary aerosol components and the interaction with precipitation and high wind speed.

The Beijing–Tianjin–Hebei region in China has been suffering from a severe particulate matter pollution, and the inter-city transport of the pollutant plays an important role. The current research quantitatively assesses the transport process. We identify three transport pathways. The southwest–northwest one happens in both winter and summer. The transport is stronger at 300–1000 m, or 1–2 days before a pollution peak. The result may guide the joint emission control along the transport pathway.

Topic 3 of the Model Inter-Comparison Study for Asia (MICS-Asia) Phase III examines how online coupled air quality models perform in simulating high aerosol pollution in the North China Plain region during wintertime haze events and evaluates the importance of aerosol radiative and microphysical feedbacks. A comprehensive overview of the MICS-ASIA III Topic 3 study design is presented.

The paper illustrates what we believe are the first measurements of a phenomenon taking place in upper portion of the convective boundary layer in clear-air conditions leading to the appearance of a persistent minimum in lidar backscatter echoes, with alternating intensifications and attenuations. The paper gives experimental evidence of the phenomenon and provides possible interpretations for its occurrence referring to both hygroscopic and scattering properties of sounded aerosol particles.

Our study first conducted a long-term observation of mixing layer height (MLH) with high resolution on the North China Plain (NCP), analyzed the spatiotemporal variations of regional MLH, investigated the reasons for MLH differences in the NCP and revealed the meteorological reasons for heavy haze pollution in southern Hebei. The study results provide scientific suggestions for regional industrial structure readjustment and have great importance for achieving the integrated development goals.

This paper serves as an introduction to the special issue "Twenty-five years of operations of the Network for the Detection of Atmospheric Composition Change (NDACC)". It describes the origins of the network, its actual status, and some perspectives for its future evolution in the context of atmospheric sciences.

Monsoon seasons are known to affect weather and climate in the Philippines. These shifting winds also cause the movement of pollutants in Asia. In this study, we found that during the northeast monsoon, pollution emissions from northern East Asia reach the northern part of the Philippines. On average, these transported pollutants make up a third of observed pollutants in the region.

Snow and ice samples were collected from six glaciers and multiple mountain valleys from northern Pakistan. Samples were analyzed for black carbon and water-insoluble organic carbon. Relatively high concentrations of black carbon, organic carbon, and dust were reported. Snow albedo and radiative forcing were estimated for the snow samples. Possible source regions of pollutants were identified through various techniques.

In this work we compare three key constituents of the middle atmosphere (ozone, NO₂, and NO₃) from the GOMOS satellite instrument with the WACCM model. We find that in the stratosphere (below 50 km) ozone differences are very small, but in the mesosphere large deviations are found. GOMOS and WACCM NO₂ agree reasonably well except in the polar areas. These differences can be connected to the solar particle storms. For NO₃, WACCM results agree with GOMOS with a very high correlation.

Atmospheric aerosols modify the radiative budget of the Earth, and it is therefore mandatory to have an accurate representation of their optical properties for understanding their climatic role. This work therefore evaluates the skill in the representation of optical properties by different remote-sensing sensors and regional online coupled chemistry–climate models over Europe.

Perfluoroalkyl acids (PFAAs) are persistent, bioaccumulative compounds found in the environment far from source regions, including the remote Arctic. We collected a 15 m ice core from the Canadian High Arctic to measure a 38-year deposition record of PFAAs, proving information about major pollutant sources and production changes over time. Our results demonstrate that PFAAs have continuous and increasing deposition, despite recent North American regulations and phase-outs.

We investigate the mismatch between incoming energy and the turbulent flux of sensible heat at the Earth's surface and how surface heterogeneity affects this imbalance. To resolve the turbulent fluxes we employ large-eddy simulations. We study terrain with different heterogeneity lengths and quantify the contributions of advection by the mean flow and horizontal flux-divergence in the surface energy budget. We find that the latter contributions depend on the scale of the heterogeneity length.

Remote sensing measurements of ethene have been made from the ground and from balloons. Ethene can be measured at low altitudes in polluted regions, such as the Los Angeles basin. Here ethene amounts have decreased by a factor of 3 over the past 25 years due to increasingly strict emission control regulations (e.g., on vehicle exhaust).

This paper represents an unprecedented pole-covering day- and nighttime climatology of the polar stratospheric clouds (PSCs) based on satellite measurements, their spatial distribution, and composition of different particle types. The climatology has a high potential for the validation and improvement of PSC schemes in chemical transport and chemistry–climate models, which is important for a better prediction of future polar ozone loss in a changing climate.

The nitrate/organic acid mixed aerosols exhibit varying phase behavior and hygroscopic growth depending upon the type of components in the particles. Our results reveal that the coexisting organic acid has considerable impacts on the phase and morphology of nitrate particles in the low and medium RH range, which thus result in obvious enhancement or suppression of water uptake with increasing RH. This new information provided here has important implications for atmospheric chemistry.

One of the most important parameters in climate science is the equilibrium climate sensitivity (ECS). Estimates of this quantity based on 20th-century observations suggest low values of ECS (below 2 °C). We show that these calculations may be significantly in error. Together with other recent work on this problem, it seems probable that the ECS is larger than suggested by the 20th-century observations.

We consider the ozone measurements from aircraft during the CAST/CONTRAST/ATTREX campaigns of 2014. Low concentrations of ozone were found in the layer of 10–15 km altitude, which is indicative of uplift of ozone-poor air from near the sea surface to 10–15 km altitude. Chemicals that have origins in the sea were found in greater abundance when ozone concentrations were low compared to when ozone concentrations were high. The lowest ozone concentrations were found in the Southern Hemisphere.

This work, part of DACCIWA WP2 Air Pollution and Health, aims to characterize urban air pollution levels through the measurement of NO₂, SO₂, NH₃, HNO₃ and O₃ at 21 measurements sites in the district of Abidjan, an important metropolis in western Africa. Results show a high spatial variability of gaseous pollutants at the scale of the district of Abidjan and the predominance of the concentration of two pollutants (NH₃ and NO₂) related to domestic fires and road traffic, respectively.

We present the first simultaneous PAN and O₃ measurements from the central Tibetan Plateau. Both gases showed unique diurnal cycles with steep rises in the early morning and broader daytime platforms, which is attributed to the PBL evolution. Some high PAN and O₃ episodes were observed and caused either by long-range transport of pollutants from south Asia or by downward transport of air masses from the upper troposphere, indicating the dynamic impacts on tropospheric chemistry over the Tibet.