This study explores future ozone radiative forcing (RF) and the relative contribution due to different drivers. Climate-induced ozone RF is largely the result of the interplay between lightning-produced ozone and enhanced ozone destruction in a warmer and wetter atmosphere. These results demonstrate the importance of stratospheric–tropospheric interactions and the stratosphere as a key region controlling a large fraction of the tropospheric ozone RF.

Our study shows that across ASEAN 50 cities, these model results reveal that 39 % of observed low-visibility days can be explained by either fossil fuel burning or biomass burning emissions alone, a further 20 % by fossil fuel burning alone, a further 8 % by biomass burning alone, and a further 5 % by a combination of fossil fuel burning and biomass burning. The remaining 28 % of observed low-visibility days remains unexplained, likely due to emissions sources that have not been accounted for.

Cirrus clouds can form by a variety of mechanisms, such as orographic uplift, through convective systems or through large-scale rising motions. In this work, an automated classification of cirrus clouds based on satellite and reanalysis data is presented to separate cirrus by these different formation mechanisms. The classification provides information on the ice origin and cloud-scale updraughts that could not be determined using satellite or reanalysis data alone.

This work describes experiments to constrain the production of secondary organic aerosol from pinanediol, a semi-volatile oxidation product of α-pinene. Our results and the implications for SOA aging are directly relevant to the atmospheric chemistry community because they connect new-particle formation experiments and SOA formation experiments. The oxidation conditions are typically different and experiments are also influenced in different ways by wall losses of condensible vapors.

Carbonaceous aerosols are related to adverse human health effects, which depend on the aerosol chemical composition and size. Here, we combine aerosol mass spectrometry and radiocarbon measurements of size-resolved samples collected over a long term to identify the origins of primary and secondary carbonaceous aerosols in the fine and coarse modes.

Weather (meteorology) has a strong effect on air quality; if not accounted for, there is uncertainty surrounding what drives features in air quality time series. We present a machine learning approach to account for meteorology using PM₁₀ data in Switzerland. With the exception of one site, all Swiss normalised PM₁₀ trends were found to significantly decrease, which validates air quality management efforts. The machine learning models were interpreted to investigate interesting processes.

The GRAPES–CUACE aerosol adjoint model was developed and applied in detecting PM_2.5 sources for haze events in eastern China (EC). The response time of Beijing PM_2.5 pollution peaks to local and surrounding emissions is quantized for regional transport of air pollution over the EC. The adjoint results agreed well with the Models-3/CMAQ assessments. The adjoint method is powerful in simulating the receptor–source relationship and can be utilized in dynamic air quality control scheme design.

The absorption Ångström exponent (AAE) of black carbon (BC) is widely accepted to be 1.0, although observational estimates give a quite wide range of 0.6–1.1. This study investigates BC AAE numerically using realistic particle properties and accurate numerical models. The significantly influence of BC microphysical properties on BC AAE is revealed by simple linear formulas, and the widely accepted BC AAE value of 1.0 is not correct for even small BC with wavelength-independent refractive index.

Atmospheric aerosols were collected in Cotonou/traffic (CT), Benin, and, Abidjan/traffic (AT), Abidjan/landfill (AL) and Abidjan/domestic fires (ADF), Côte d'Ivoire, from February 2015 to March 2017. We report the weekly PM_2.5, elemental (EC) and organic (OC) carbon, and aerosol optical depth (AOD) in both cities. PM_2.5 was 32 ± 32, 32 ± 24, 28 ± 19 and 145 ± 69 µg m⁻³ at CT, AT, AL and ADF. OC / EC is 3.5 at CT, 2.0 at AT, 2.2 at AL and 5.2 at ADF. AOD is 0.58 at Cotonou and 0.68 at Abidjan.

The nocturnal nitrogen oxides dinitrogen pentoxide (N₂O₅) and its heterogeneous uptake product nitryl chloride (ClNO₂) can have profound impacts on air quality, yet their abundances and chemistry are only sparsely constrained by field measurements. Here, we present the first measurements of N₂O₅ and ClNO₂ in the Lower Fraser Valley of British Columbia, Canada. Concentrations were lower than have been observed elsewhere. Morning peaks indicate higher ClNO₂ production above the measurement site.

A lack of policy-relevant metrics for hydrochlorofluorocarbons (HCFCs) regulated in the Montreal Protocol is addressed by providing reliably estimated metrics for all HCFCs included in the protocol. This research provides reliable policy-relevant metrics (e.g., atmospheric lifetimes, ozone depletion and global warming potentials) based on well-established estimation methods. The results from this work provide the Montreal Protocol the information needed for informed policy decisions.

The phase transition of organic particles between glassy and semi-solid states occurs at the glass transition temperature. We developed a method to predict glass transition temperatures and the viscosity of secondary organic aerosols using molecular composition, with consistent results with viscosity measurements. The viscosity of biomass burning particles was also estimated using the chemical composition measured by high-resolution mass spectrometry with two different ionization techniques.

Using satellite products of MODIS and the numerical model of WRF-DUST, we proved that the ecological restoration programs in China help to reduce the dust pollution in the NCP, providing a direct and quantified answer to the ongoing debate about the effectiveness of the national ERPs. Despite the limitations of the case study, we provide some insights into the effects of ERPs on the downwind area, where heavy haze often occurs due to anthropogenic air pollutants.

We measured gas- and particle-phase amine and ammonia concentrations in a boreal forest site in 2015 with online ion chromatography coupled with mass spectrometry. We wanted to know how much and which kinds of amines there are, and how they behave and could affect nucleation. We observed seasonal and diurnal variations for different amines. Amines turned out to be a heterogeneous group of compounds. To our best knowledge, our amine measurements are the longest time series that has been made.

Atmospheric nitrate may be produced locally and/or come from upwind regions. To address this issue we measured oxygen and nitrogen isotopes of wet and dry nitrate deposition at nearby urban and rural sites. Our results suggest that, relative to nitrate in wet deposition in urban environments and wet and dry deposition in rural environments, nitrate in dry deposition in urban environments results from local NO_x emissions more so than wet deposition, which is transported longer distances.

A numerical model also used for operational weather forecast was applied to investigate the impact of contrails and contrail cirrus on the radiative fluxes at the earth's surface. Accounting for contrails produced by aircraft enables the model to simulate high clouds that are otherwise missing. In a case study, we find that the effect of these extra clouds is to reduce the incoming shortwave radiation at the surface as well as the production of photovoltaic power by up to 10 %.

Soil moisture influences the occurrence of convective precipitation. An accurate knowledge of soil moisture might improve the prediction of convective cells. But the model uncertainty overshadows the impact of soil moisture in convection resolving models. Only drastic soil moisture changes can exhibit the model uncertainties. Both the enhanced and reduced soil moisture result in a reduced precipitation rate. We point out the need for uncertainty estimations in soil moisture studies.

We point out the representativeness of single lidar stations for zonally averaged ozone profile variations in the middle/upper stratosphere. We examine the contribution of chemistry and natural proxies to ozone profile trends. Above 10 hPa an “inflection point” between 1997–99 marks the end of significant negative ozone trends, followed by a recent period of positive ozone change in 1998–2015. Below 15 hPa the pre-1998 negative ozone trends tend to become insignificant as we move to 2015.

Deposition of light-absorbing carbonaceous aerosol on the surface of glaciers can greatly alter the energy fluxes of glaciers. Two years of continuous observations of carbonaceous aerosols in a glacierized region are analyzed. We mainly studied the light absorption properties of carbonaceous aerosol and have employed a global aerosol–climate model to estimate source attributions of atmospheric black carbon.

This overview discuss the main precipitation processes and their sensitivities to environmental conditions in the Central Amazon Basin. It presents a review of the knowledge acquired about cloud processes and rainfall formation in Amazonas. In addition, this study provides a characterization of the seasonal variation and rainfall sensitivities to topography, surface cover, and aerosol concentration. Airplane measurements were evaluated to characterize and contrast cloud microphysical properties.

We use observations of boundary layer methane from the SEAC4RS aircraft campaign over the Southeast US to estimate methane emissions in that region. Our results suggest that the EPA inventory is regionally unbiased but there are large local biases, suggesting variable emission factors. Our results also suggest that the choice of landcover map is the dominant source of error for wetland emission estimates.

The vertical profiles of convection in the Amazon are sampled using CloudSat, with particular emphasis on day–night contrast. Focusing on vigorous deep convective cores reveals a distinct, previously unreported double-arc reflectivity feature in the contoured frequency by altitude diagram, likely corresponding with two modes of ice hydrometeor phase: snow versus graupel/hail. Replicating this feature in cloud-resolving models requires further improvements in the microphysical parameterization.

We show the main drivers of high O₃ episodes in and around Madrid. High levels of ultrafine particles (UFPs) are evidenced, but we demonstrate that most O₃ arises from the fumigation of high atmospheric layers, whereas UFPs are generated inside the PBL. O₃ contributions from the fumigation of the vertical recirculation of regional air masses, hemispheric transport, and horizontally from direct urban plume transport are shown. Complexity arises from the need to quantify them to abate surface O₃.

The cryosphere of the Earth overlaps with the atmosphere, hydrosphere and lithosphere over vast areas with temperatures below zero C and pronounced H₂O phase changes. The cryosphere plays the role of a global thermostat; however, the processes related to the cryosphere attract insufficient attention from research communities. We call attention to crucial importance of cryogenic anomalies, which make the Earth atmosphere and the entire Earth system unique.

Grouping data on the basis of (dis)similarity can be used to assess the efficacy of monitoring networks. The data are cross-compared in terms of temporal variation and magnitude of concentrations, and sites are ranked according to their level of potential redundancy. The methodology can be applied to measurement data, helping to identify sites with different measuring technologies or data flaws, and to model output, generating maps of areas of spatial representativeness of a monitoring site.

In 1926, total ozone series started in Arosa (Switzerland). Since the mid-1970s ozone is measured to document the effects of anthropogenic ozone-depleting substances (ODSs). ODSs peaked around the mid-1990s, resulting from the Montreal Protocol (1987) and its enforcement. Chemical ozone depletion stopped worsening around the mid-1990s but the large variability complicates demonstrations of the success of the protocol and the effect of ongoing climate change still requires continuous measurement.

Hazard reduction burns (HRBs) may prevent wildfires, but both generate PM_2.5 air pollution. We identify the meteorological factors linked to high PM_2.5 pollution & assess how they differ between HRB days with low vs. high PM_2.5. Boundary layer, cloud cover, temperature & wind speed strongly influence PM_2.5, with these factors being more variable & higher in magnitude during mornings & evenings of HRB days when PM_2.5 remains low, indicating how HRB timing can be altered to reduce air pollution.

The cleansing capacity of the atmosphere is studied through the hydroxyl radical (OH) chemical reactivity in numerical simulations of natural and urban environments. Turbulence-driven segregation of chemical compounds in the atmospheric boundary layer is explored and may partially explain discrepancies between observed and modeled OH reactivity in both environments.

Chloromethane is involved in stratospheric ozone depletion, but detailed knowledge of its global budget is missing. In this study stable hydrogen isotope analyses were performed to investigate the dominant loss process for atmospheric chloromethane with photochemically produced hydroxyl radicals. The findings might have significant implications for the use of stable isotope signatures in elucidation of global chloromethane cycling.

This study provides a quantified and mechanistic understanding of the radiative effects of ozone waves on the NH stratosphere. In particular, we find these effects to influence the seasonal evolution of the midlatitude QBO signal (Holton–Tan effect), which is important for getting realistic dynamical interactions in climate models. We also provide a synoptic view on the evolution of the seasonal development of the Holton–Tan effect by looking at the life cycle of upward-propagating waves.

A potential aerosol mass (PAM) reactor expedites slow atmospheric oxidation reactions and enables the observation of chemical aging processes and the determination of the aerosol-forming power of an air mass. A PAM reactor was deployed at Baengnyeong Island in the Yellow Sea. Experimental results confirm the key role of SO₂ in generating secondary aerosols in northeast Asia, and the contribution of organics to secondary aerosols is more variable during transport in the atmosphere.

The reaction of SO₂ with NO₂ on particles is proposed to be one major pathway of sulfate formation in the polluted atmosphere. We found that in the reaction of SO₂ with NO₂ on CaCO₃ particles, presence of O₂ enhanced the uptake rate of SO₂ by 2–3 orders of magnitude compared with the reaction of SO₂ directly with NO₂. O₂ was the main oxidant of SO₂ and NO₂ was the initializer of chain reactions. The multiphase oxidation of SO₂ by NO₂/O₂ can be an important source of sulfate in the atmosphere.

Often, the emission height of the mesospheric hydroxyl layer has been inferred from a comparison of temperature measured by ground-based lidars and hydroxyl spectrometers. I use temperatures measured by two independent instruments to show that such comparisons usually lead to ambiguous height determinations, especially if a variable layer width is taken into account. Even though this dataset is from a single location, the results apply to all airglow layers at any location.

This paper investigates how large-scale weather systems control fine particulate matter (PM_2.5) air quality in China. We show that winter monsoons, onshore winds and frontal rains can drive daily PM_2.5 variability in different regions of China. We further project future PM_2.5 concentration change by 2050s due to climate change, and verify that climate change has little benefit on future PM_2.5 in Beijing, implying cutting down emissions is necessary to mitigate pollutions in megacities of China.

One of the most prominent asymmetric features of the southern hemispheric (SH) circulation is the split jet over Australia and New Zealand in austral winter. We propose a new, hemispherical index that is based on the principal components (PCs) of the zonal wind field for the SH winter. The new PC-based index (PSI) suggests that the SH split jet is strongly associated with the AAO. Furthermore, both flavors of ENSO and the PSA-1 pattern produce favorable conditions for a SH split event.

In this paper we distill the problem of aerosol–cloud interactions to an interplay between the system's two characteristic vertical velocities, i.e., the air vertical velocity and the collective droplets fall velocity. We show using theoretical considerations and cloud-resolving models that the relations between the two velocities are extremely sensitive to the cloud field's thermodynamics and microphysical properties.

This paper investigates the modulation effect of ABL meteorology on Beijing’s surface air quality based on self-organizing maps. The self-organized ABL types correspond to significantly distinct pollutant loadings and diurnal evolution, particularly in winter. Anomalous stable ABL conditions are estimated to contribute 58.3 %, 46.4 % and 73.3 % of the elevated PM2.5 concentrations in January 2013, December 2015 and December 2016.

NASA's Orbiting Carbon Observatory 2 (OCO-2) satellite observes CO₂ in the atmosphere globally. We evaluate the extent to which current OCO-2 observations can inform scientific understanding of the biospheric carbon balance. We find that current observations are best-equipped to constrain the biospheric carbon balance across continental or hemispheric regions and provide limited information on smaller regions.

We used satellite observations and model simulations of CFC-11, CFC-12, and N₂O to investigate stratospheric transport, which is important for predicting the recovery of the ozone layer and future climate. We found that sampling can impact results and that the model consistently overestimates concentrations of these gases in the lower stratosphere, consistent with a too rapid Brewer–Dobson circulation. An issue with mixing in the tropical lower stratosphere in June–July–August was also found.

We study the distributions of sulfur and nitrogen deposition, which are associated with current environmental issues such as formation of acid rain and ecosystem eutrophication and result in widespread problems such as loss of environmental diversity, harming the crop yield and even food insecurity. According to our study, both the amount and distribution of sulfate and nitrogen deposition have changed significantly in the last decade, particularly in East Asia, South Asia and Southeast Asia.

The Mediterranean Basin still suffers from a limited amount of in situ measurements for a good characterization of its environmental state. This study shows that intercontinental transport of very high CO concentrations can affect the upper Mediterranean Basin troposphere. By using modeling, 5- to 12-day eastward transport of biomass burning starting from North America and Siberia impacts the mid-troposphere of the Mediterranean Basin.

Measurements of mercury fluxes over snow surfaces are carried out at the High Arctic site at Villum Research Station in North Greenland. The measurements were carried out from 23 April to 12 May during spring 2016, where atmospheric mercury depletion events (AMDEs) took place. The measurements showed a net emission of 8.9 ng m⁻² min⁻¹, with only a few depositional fluxes. GEM fluxes and atmospheric temperature measurements suggest that GEM emission partly could be affected by surface heating.

Tropospheric ozone (O₃) is the third most important greenhouse gas. Several sensors on satellites measure O₃ concentration like the infrared sounding IASI of MetOp satellites with a spatiotemporal coverage never reached so far. The assimilation of tropospheric IASI data within the chemistry transport model MOCAGE gives a good representation of O₃ variability over the tropics linked with ENSO and the Walker circulation. IASI assimilation can contribute to the long-term monitoring of O₃.

The radon progeny can describe the circulation of air masses in the Arctic region, evidencing a seasonality and stability dynamics that can influence the persistence of pollutants in the lower layer of the atmosphere. This paper, for the first time, considered high-time resolved radon-progeny measurements in the Arctic region. These data were used for tracing air masses in terms of age, origin, permafrost dynamics, seasonality and local effects.

Different kinds of waves are the subject of intense research because they are suspected to steer several different atmospheric phenomena. To analyse the effects of waves, wave packet characteristics have to be known. We introduce a new tool to study wave packets locally: Unified Wave Diagnostics (UWaDi). To show the advantages of UWaDi, a sudden stratospheric warming period in 2016 is analysed for different background wind conditions, revealing gravity waves emitted from a jet exit region.