An eastward advection of dry and warm air in spring was identified as a major drought onset mechanism over the US Great Plains (GP). Further breakdown of the zonal advection into the dynamic versus thermodynamic contributions revealed dominance of the latter in the tropospheric drying observed during the onset of GP 2011 and 2012 droughts. The dependence of thermodynamic advection on moisture gradient links the spring precipitation in the Rockies and US southwest to the GP summer precipitation.

Three aircraft datasets from the DACCIWA campaign in summer 2016 are used here to show there is a background mass of pollution present in the lower atmosphere in southern West Africa. We suggest that this likely comes from biomass burning in central and southern Africa, which has been carried into the region over the Atlantic Ocean. This would have a negative health impact on populations living near the coast and may alter the impact of growing city emissions on cloud formation and the monsoon.

Cutting short-lived pollutants can help keep cool the climate – but only if we are clever. We investigate how regional temperatures may change in response to different packages of air quality measures. One package consists of mitigation measures that mainly target emissions that are known to result in a cooler climate, while in the other, emissions are cut as much as technically possible in response to air quality concerns. We estimate the different contributions from various sectors and region.

We use an air quality model with a modified organic aerosol (OA) module based on chamber experiments to identify the OA sources and their contributions in Europe. Comparisons with long-term measurements at nine sites in 2011 show an improvement in OA simulation. Our results suggest that the biomass burning and biogenic emissions are the dominant sources in winter and summer, respectively. Contributions of diesel and gasoline vehicles are relatively small compared to a previous study in the US.

This work reports direct measurements of sea spray fluxes from a coastal site in the UK, which are relevant for atmospheric chemistry as well as coastal air quality. Sea spray fluxes from this location are roughly an order of magnitude greater than over the open ocean at similar wind conditions, comparable to previous coastal measurements. Unlike previous open ocean measurements that are largely wind speed dependent, we find that sea spray fluxes near the coast depend more strongly on waves.

Ice crystals in clouds have a wide variety. But many crystal forms are inexplicable using the common approach of modeling the growth rates normal to the crystal faces. Instead of using only this normal-growth approach, we suggest including lateral facet growth processes. Using such lateral processes, backed up by new experiments, we give explanations for some of these puzzling forms. The forms include the center droxtal in stellar crystals, scrolls, capped columns, sheath bundles, and trigonals.

The abundance and distribution of reactive halogen species and their impact on air quality in Europe are poorly understood. We adopt a state-of-the-art regional model (CMAQ) to evaluate such effects, and the results demonstrate the significant influence of halogen chemistry on the capacity of atmospheric oxidation and the formation of air pollutants in Europe. Our study highlights the necessity of including halogen chemistry in the formulation of air pollution control policy.

NO₂ tropospheric vertical columns (TVCDs) and surface concentrations are widely used proxies for NO_x emission variations. Through model and observation analyses, we find that satellite NO₂ TVCDs provide much better information on anthropogenic NO_x emission variations over urban than rural regions. NO₂ surface observations, satellite column datasets, and EPA anthropogenic NO_x emissions show consistent annual variations over urban regions of the United States with a continuous decrease after 2011.

Mineral dust is lifted into the atmosphere from desert regions, where it can be transported over thousands of kilometres around the world. Dust impacts weather, climate, aviation, and air quality. We evaluate new aircraft observations of dust size. We find that the largest particles typically omitted by models have a significant impact on the interactions of dust with radiation and therefore climate. We also find that large dust particles are retained in the atmosphere longer than expected.

In this study, a 3–D Stockwell transform is applied to AIRS–Aqua satellite observations in the first extended 3–D study of stratospheric gravity waves over the Southern Ocean during winter. A dynamic environment is revealed that contains some of the most intense gravity wave sources on Earth. A particularly striking result is a large–scale meridional convergence of gravity wave momentum flux towards latitudes near 60 °S, something which is not normally considered in model parameterisations.

The effect of aerosol–cloud interactions (ACIs) on Earth's energy budget continues to be highly uncertain. We decompose the effective radiative forcing by ACIs (ERF_aci) into the instantaneous forcing due to anthropogenic increases in the number of cloud droplets and fast responses of cloud properties to the droplet number perturbation in the ECHAM–HAMMOZ aerosol–climate model. This decomposition maps onto the IPCC's Fifth Assessment Report analysis of ERF_aci more directly than previous work.

Gravitational waves (GWs) with periods ranging from 10 to 30 min over 10 h and 20 wave cycles are detected within a 2 km height in the atmospheric boundary layer (ABL) by a coherent Doppler wind lidar. Observations and computational fluid dynamics (CFD) simulations lead to a conclusion that the GWs are excited by the wind shear of a low-level jet under the condition of light horizontal wind. The GWs are trapped in the ABL due to a combination of thermal and Doppler ducts.

Aerosols over the Southern Ocean consist primarily of sea salt and sulfate, yet are seasonally biased in our model. We test three sulfate chemistry schemes to investigate DMS oxidation, which forms sulfate aerosol. Simulated cloud droplet number concentrations improve using more complex sulfate chemistry. We also show that a new sea spray aerosol source function, developed from measurements made on a recent Southern Ocean research voyage, improves the model's simulation of aerosol optical depth.

This study provides quantitative information regarding the source contributions of the major non-methane volatile organic compound sources in Mohali in the northwestern Indo-Gangetic Plain. Combining in situ data and model analyses, we show that residential biofuel use and waste disposal emissions as well as the VOC burden associated with solvent use and industrial sources are overestimated by all emission inventories.

Long-term cloud condensation nuclei (CCN) number concentration (NCCN) data are scarce; there are a lot more data on aerosol optical properties (AOPs). It is therefore valuable to derive parameterizations for estimating NCCN from AOP measurements. With the new parameterization NCCN can be estimated from backscatter fraction, scattering Ångström exponent, and total light-scattering coefficient. The NCCN–AOP relationships depend on the geometric mean diameter and the width of the size distribution.

This paper presents a new dataset of laboratory measurements of the shortwave (SW) spectral complex refractive index and single-scattering albedo (SSA) for global mineral dust aerosols of varying origin and composition. Our results show that the dust refractive index and SSA vary strongly from source to source, mostly due to particle iron content changes. We recommend that source-dependent values of the SW spectral refractive index and SSA be used in models and remote sensing applications.

Energy consumption in Asia has substantially risen since 1970, leading to increased levels of air pollution, which can have severe impacts on human health and the environment. We present the first continuous ice-core record of toxic trace metals that covers 1971–2015. This new record from the Guliya ice cap in northwestern Tibet shows that Pb, Cd, Zn, and Ni, emitted mostly from fossil fuel combustion and biomass burning in South Asia, have reached the remote, high-altitude glacier since 1990.

We investigated the change in cloud droplet activity of size-selected soot particles after being exposed to atmospheric levels of ozone over the course of 12 h. For this, we operated a 3 m³ aerosol chamber in continuous-flow mode. The results were fed into a climate model (ECHAM-HAM). We found that the oxidation of soot particles with ozone is a significant source of cloud condensation nuclei in the atmosphere.

Wet deposition is one of the most important and efficient removal mechanisms in the evolution of the air pollution. Due to the lack of a localized parameterization scheme and some mechanisms being neglected in theoretical estimations and modeling calculations, below-cloud wet scavenging coefficients (BWSC) have large uncertainties. We compare the BWSCs under the same conditions to perform a multi-method evaluation in order to describe their characteristics.

Dusts have a significant impact on climate and environment. Detecting dust using satellite instruments is generally conducted by measuring at multiple observation angles due to the uncertainty of the surface reflection. This report shows that the degree of polarization of reflected light can be used for retrieving the optical depth of dust at backscatter angles only, regardless of surface conditions. This simple method is suitable for surveying dust aerosols over oceans with low-cost satellites.

One of the most important processes in the global mercury biogeochemical cycling is the deposition of atmospheric mercury to the land surfaces. In this paper, results of wet, dry, and forest Hg deposition from global observation networks, individual monitoring studies, and observation-based simulations are reviewed. Uncertainties in the observation and simulation of global speciated atmospheric Hg deposition to the land surfaces are systemically estimated.

We present a 1-year source apportionment record of carbonaceous aerosols in Xi'an, China. Biomass burning strongly increases in winter, while seasonal changes of coal and liquid fossil fuel combustion are moderate. We find strong evidence for fossil secondary OC formation during the warm period that is further enhanced in stagnant, polluted conditions due to longer atmospheric residence times. At the same time we find that water-insoluble (primary) fossil is lost due to photochemical processing.

The Asian and North American summer monsoons (ASM and NASM) have considerable influence on stratospheric chemistry and physics. More air mass is transported from the monsoon regions to the tropical stratosphere when the tracers are released clearly below the tropopause than when they are released close to the tropopause. Results for different altitudes of air origin reveal two transport pathways (monsoon and tropical) from the upper troposphere over the monsoon regions to the tropical pipe.

We present, for the first time, the dual effect of GDI-vehicle exhaust on α-pinene SOA mass yield suppression. The first effect is a well-known NOx effect, but the second effect is more complex. Our results imply that this second effect is related to change of reaction pathways of α-pinene in the presence of GDI exhaust. The presence of vehicle exhaust caused more than 50 % suppression in α-pinene SOA mass yield compared to the α-pinene SOA mass yield measured in the absence of GDI emissions.

We review the literature to refine the definition of "tar balls" (or tar particles). Then, using a marine-engine data set, we show that a standard SP2 can identify tar particles in two ways, as evaporating and non-incandescing (30 % of tar particles by number) or incandescing particles which scatter more light than soot at incandescence (70 % of tar particles by number). To our knowledge, no other technique can provide in situ, real-time evidence for the presence of tar particles in an aerosol.

Ammonium nitrate is a major component of fine particulate matter of wintertime air pollution in the Great Salt Lake Region (UT, USA). We investigate the sources of ammonia in the region by using aircraft observations and comparing them to modelled ammonia mixing ratios based on emission inventory estimates. The results suggest that ammonia emissions are underestimated, specifically in regions with high agricultural activity, while ammonia in Salt Lake City is mainly of local origin.