Atmospheric isoprene oxidation has an important effect on the formation of pollutants such as ozone and particles. A reliable representation is an essential component of climate change/air quality models. Systematic updates to the detailed chemistry in the MCM are described, with reference to recently reported kinetic/mechanistic data. Results of box model calculations are used to illustrate the impacts of the updates, with particular focus on the key atmospheric cycles involving HOx and NOx.

After volcanic eruptions different radiative and chemical processes take place in the stratosphere which perturb the ozone layer and cause pronounced dynamical changes. In idealized chemistry-climate model simulations the importance of these processes and the modulating role of the climate state is analysed. The chemical effect strongly differs between a preindustrial and present-day climate, but the effect on the dynamics is weak. Radiative processes dominate the dynamics in all climate states.

The model and MIPAS satellite data show that there are three regions which contribute substantial pollution to the south Asian UTLS: the Asian summer monsoon (ASM), the North American monsoon (NAM) and the West African monsoon (WAM). However, penetration due to ASM convection reaches deeper into the UTLS compared to NAM and WAM outflow. Simulations show that westerly winds drive North American and European pollutants eastward where they can become part of the ASM and lifted to LS.

We have conducted a perturbed parameter model ensemble to investigate Mt. Pinatubo's 1991 initial sulfur mass emission. Our results suggest that (a) the initial mass loading of the Pinatubo eruption is ~14 Mt of SO2; (b) the injection vertical distribution is strongly skewed towards the lower stratosphere, leading to a peak mass sulfur injection at 18-21 km; (c) the injection magnitude and height affect early southward transport of the volcanic cloud observed by SAGE II.

This paper presents first observations of smoke-induced density currents, which are a boundary-layer flow phenomenon resulting from radiative shading by wild fire smoke. Our analysis uses a mobile Doppler lidar to reveal the anatomy and evolution of one such density current in northern California. The results show that these density currents can flow counter to the ambient wind and spread over long distances (e.g. 25km), causing unexpected smoke impacts.

We tag BC emissions from 13 source regions around the globe in a global chemical transport model MOZART-4 and optimize the aging timescale for each source region by minimizing errors in vertical profiles of BC mass mixing ratios between simulations and HIAPER Polo-to-Pole Observations (HIPPO). We find that the optimized aging timescale of BC varies significantly by region and season. Our simulations indicate that BC lifetime increases nearly linearly with aging timescale for all source regions.

We show that during the springtime of 2013, the anthropogenic pollution particularly from sources in Asia, contributed significantly to black carbon across the European Arctic free troposphere. In contrast to previous studies, the contribution from open wildfires was minimal. Given that Asian pollution is likely to continue to rise over the coming years, it is likely that the radiative forcing in the Arctic will also continue to increase.

Both radiative and latent heat components of total diabatic heating influence Indian monsoon dynamics. This study investigates radiative component in detail, focusing on various cloud types that have largest radiative impact during summer monsoon over the Indian subcontinent. The vertical structure of radiative heating and its intra-seasonal variability is investigated with particular emphasis on the upper troposphere and lower stratosphere (UTLS) region.

The previously expected linear relationship between atmospheric CO2 and climate variables including temperature is showing an increasing mismatch. This paper nonetheless provides fresh and possibly definitive support for a major relationship between CO2 and climate. Granger causality analysis provides evidence that change in level not level of CO2 primarily influences both global temperature and the El Niño–Southern Oscillation. The results may contribute to the prediction of future climate.

The mineral composition of dust aerosols is modeled. The mineral composition is derived by extending a method that provides the composition of wet-sieved soil to account for differences between the mineral fractions of the wet-sieved soil and the resulting aerosol concentration. An empirical constraint upon the relative emission of clay and silt is applied that further differentiates soil and aerosol mineral composition. A method is proposed for mixing minerals with iron oxide impurities.

A global compilation from nearly sixty measurement studies is used to evaluate two methods of simulating the mineral composition of dust aerosols. Dust emission based on wet-sieved soil is assumed for the first method. The second method reconstructs the aggregates and size distribution of the emitted dust aerosols. Only the second method is able to reproduce observed phyllosilicate fractions in the silt size range and reduces quartz overestimation. Substantial uncertainties remain.

To understand the contribution of anthropogenic dust to the total global dust load, a new technique for distinguishing anthropogenic dust from natural dust is proposed by using CALIPSO dust measurements and PBL height retrievals along with a land use data set. Results reveal that local anthropogenic dust aerosol accounts for about 25% of the global continental dust load.

This work presented a new method of quantifying water-soluble elements in PM2.5 aqueous extracts (N~500) with an X-ray fluorescence analyzer. The results indicate that water-soluble elements had marked spatial and temporal patterns. Four sources were resolved: brake/tire wear, biomass burning, secondary formation, and mineral dust. The findings have informed studies on aerosol oxidative potential and provided insights into the health effects of water-soluble metals, especially Cu, Fe, Mn and Zn.

We investigated inorganic N wet deposition at five sites in the Tibetan Plateau (TP). Combining in situ measurements in this and previous studies, the average wet deposition of NH4+-N, NO3--N, and inorganic N in the TP was estimated to be 1.06, 0.51, and 1.58 kg N ha−1 yr−1, respectively. Results suggest that earlier estimations based on chemical transport model simulations and/or limited field measurements likely overestimated substantially the regional inorganic N wet deposition in the TP.

During the CARRIBA campaign on Barbados, 91 cases with increased aerosol particle number concentrations near clouds were detected from helicopter-borne measurements. Most of these cases are correlated with enhanced irradiance in the ultraviolet range. The events have a mean length of 100m, corresponding to a lifetime of 300s, meaning a growth of several nm/h. Such high values cannot be explained by sulfuric acid alone; thus extremely low volatility organic compounds are probably involved here.

Airbus measurements at elevations circa 11 km within large storm systems near Darwin and Santiago indicate ice mass distributed over area-equivalent diameters of 100-500 µm. Profiler-observed radar reflectivity and mean Doppler velocity under similar conditions are found to be consistent with measurements and with 1D simulations of steady-state stratiform rain columns initialized with observed ice size distributions. Results motivate investigation of ice formation pathways in Part II.

An updraft parcel model with size-resolved microphysics is used to investigate microphysical pathways leading to ice water content > 2 g m-3 with mass median area-equivalent diameter of 200-300 micron reported at ~11 km in tropical deep convection. Parcel simulations require substantial source of small crystals at temperatures > ~-10 deg C growing by vapor deposition. Warm rain in weaker updrafts surprisingly leads to greater ice mass owing to reduced competition for available water vapor.

Marine-produced short-lived trace gases such as halocarbons and DMS significantly impact atmospheric chemistry. To assess this impact on ozone depletion and the radiative budget, it is critical that their marine emissions in atmospheric chemistry models are quantified as accurately as possible. We show that calculating emissions online with an interactive atmosphere improves the agreement with current observations and should be employed regularly in models where marine sources are important.

The upper troposphere and lower stratosphere (UTLS) is characterized by strong gradients in the distribution of long-lived tracers, which are sensitive to discrepancies in transport in models. We found that our model overestimates CO2 in the polar UTLS through comparison of modeled CO2 with aircraft observations. We then corrected the modeled CO2 and quantified the impact of the correction on the flux estimates using an atmospheric model together with atmospheric CO2 measured from a satellite.

A low bias in carbon monoxide (CO) at northern latitudes is a common feature of chemistry climate models. We find that increasing Northern Hemisphere (NH) CO emissions or reducing NH OH concentrations improves the agreement with CO surface observations, but reducing NH OH leads to a better comparison with MOPITT. Removing model biases in ozone and water vapor increases the simulated methane lifetime, but it does not give the 20% reduction in NH OH suggested by our analysis of the CO bias.

This work summarized all the studies reporting isoprene epoxydiols-derived secondary organic aerosol (IEPOX-SOA) measured globally by aerosol mass spectrometer and compare them with modeled gas-phase IEPOX, with results suggestive of the importance of IEPOX-SOA for regional and global OA budgets. A real-time tracer of IEPOX-SOA is thoroughly evaluated for the first time by combing multiple field and chamber studies. A quick and easy empirical method on IEPOX-SOA estimation is also presented.

We investigate stratospheric aerosol geoengineering with solid particle injection by modeling the fractal structure of alumina aerosols and their interaction with background sulfate. We analyze the efficacy (W m^-2 of radiative forcing per megaton of injection) and risks (ozone loss, s) for both alumina and diamond particles as a function of injected monomer radius, finding 240nm alumina and 160nm diamond optimal. We discuss the limitations of our 2-D model study and associated uncertainties.

Formaldehyde columns from two space sensors, GOME-2 and OMI, constrain by inverse modeling the global emissions of HCHO precursors in 2010. The resulting biogenic and pyrogenic fluxes from both optimizations show a very good degree of consistency. The isoprene fluxes are reduced globally by ca. 10%, and emissions from fires decrease by ca. 35%, compared to the prior. Anthropogenic emissions are weakly constrained except over China. Sensitivity inversions show robustness of the inferred fluxes.

The chemical composition of wood-combustion soot is investigated using a soot-particle aerosol mass spectrometer. The analysis elucidates real-time information on BC oxygenated surface functional groups for a real-world source for the first time. Additional insights into the source of organic material in this soot are provided by positive matrix factorization of the data using a new AMS error model.

A method is reported for retrieving super-thin cloud optical depth with polarized light. It is found that near-backscatter p-polarized light is sensitive to clouds, but not to ocean conditions. Near-backscatter p-polarized intensity linearly relates to super-thin cloud optical depth. Based on these findings, super-thin cloud optical depth can be retrieved with little effect from surface reflection.

We developed a new indicator, Siberian High position index (SHPI), which depicts the mean longitudinal position of the SH, as a new indicator of the large-scale circulation pattern that controls wintertime air quality in China. This SHPI explains 58% and 64% of the interannual variability of winter AOD during 2001-2013 over North China and South China, respectively. The extreme PM pollution of January 2013 is found to be associated with extremely high values of SHPI.

We estimate decadal trends in land carbon fluxes and emissions of biogenic volatile organic compounds (BVOCs) during 1982-2011, with a focus on the feedback from biosphere (such as tree growth and phenology). Increases of LAI at peak season accounts for ~25% of the trends in GPP and isoprene emissions at the northern lands. However, phenological change alone does not promote regional carbon uptake and BVOC emissions.

Internal structures are common in atmospheric dust particles, yet their effects on light scattering are largely unstudied. In this work, we study how hematite nodes, internal voids and hematite-rich coating impact single-scattering properties of computationally generated irregular model particles. The results show that all of these features change scattering properties significantly, and that a simple effective-medium approximation is not enough to replicate the scattering properties.

Simultaneous measurements of concentrations and above-canopy fluxes of isoprene and α-pinene in a forest, along with their oxidation products in aerosols, suggest that the inflow of anthropogenic precursors/aerosols enhanced the formation of both isoprene- and α-pinene-derived secondary organic aerosol (SOA) within the forest canopy even when the flux was low. We also emphasize the role of vegetation/soils near the forest floor as important sources of isoprene and α-pinene in the forest.

We perform a positive matrix factorization (PMF)-based source apportionment by combining GHG measurements with coincident VOC measurements in the San Joaquin Valley of California. Using VOCs as source tracers, we identify dairies and livestock as major sources of CH4 and N2O in the region. Agriculture is a significant source of N2O enhancements too, while vehicle emissions are found to be a negligible source of N2O. The findings are relevant to the state’s GHG inventory verification process.

Different monthly variation patterns of aerosol optical depth are observed over the southern and northern Tibetan Plateau (TP). A dividing line of higher dust occurrence in the northern TP and lower dust occurrence in the southern TP can be observed clearly at an altitude of 6-8km. The different seasonal variation patterns between the northern and southern TP are due to many factors, including the emission sources, high-altitude terrain and atmospheric circulation.

In this paper, we describe the development of a numerical model which aims at representing nitrate recycling at the air-snow interface on the East Antarctic Plateau. Stable isotopes are used as diagnostic and evaluation tools by comparing the model's results to recent field measurements of nitrate and key atmospheric species at Dome C, Antarctica. From sensitivity tests conducted with the model, we propose a framework for the interpretation of the nitrate isotope record in deep ice cores.