Speciated atmospheric Hg measurements from five high-elevation sites were compared with a global mercury model. The comparison confirmed that reactive mercury is formed in dry free tropospheric air from the oxidation of elemental Hg, more so in the summer than in other seasons. Simulations run with OH-O3 oxidation instead of the Br oxidation mechanism compared more closely with observations at desert sites, suggesting future simulations should include multiple reaction mechanisms simultaneously.

Carbonaceous aerosols recorded in a Tibetan glacier present a distinct seasonal dependence and an increasing trend after 1980, which has important implications for the accelerated glacier melting. We use a global aerosol--climate model to quantify the aerosol source--receptor relationships, showing that emissions in South Asia had the largest contribution. The emission inventories and historical fuel consumption in South Asia are consistent with our ice-core analysis and model results.

We use a homogeneous 10-year record of satellite data to study recent trends in NO2 over the world's major urban agglomerations. The results indicate distinct spatial patterns in trends, with moderate but consistent reductions in NO2 throughout most developed countries and rapid increases of up to 15 % per year over many sites in Asia, Africa, and South America. We also show links between urban NO2 trends and economic as well as demographic factors, and how the latter drive regional differences.

Precipitation is necessary but insufficient for transformation to open cells from closed cells. The transformation to open cells occurs for sufficiently small droplet number concentration and/or large rain area. Both of these factors appear to be of similar importance. The distance selects the resulting state for rain regions that alone are too weak to initiate the transformation. The phase trajectory of the variance and mean cloud field properties follow one path.

Model simulations were performed with increased HONO emissions from mobile sources that reflect recent measurements at high-traffic urban sites. These higher emissions resulted in increased morning concentrations of HONO and OH. O3 concentrations were only marginally altered. Comparison with observed data shows that HONO morning peak concentrations are better predicted by the model when the higher emissions are utilized in the simulation.

Using measurements acquired from a Zeppelin airship during the PEGASOS 2012 campaign, we show that VOC oxidation alone cannot account for the formaldehyde concentrations observed in the morning over rural Italy. Vertical profiles suggest a ground-level source of HCHO. Incorporating this additional HCHO source into a photochemical model increases calculated O3 production by as much as 12%.

Source apportionment of fine carbonaceous aerosols using radiocarbon and other organic markers measurements during 2013 winter haze episodes was conducted at four megacities in China. Our results demonstrate that fossil emissions predominate EC with a mean contribution of 75±8%, whereas non-fossil sources account for 55±10% of OC; and the increment of TC on heavily polluted days was mainly driven by the increase of secondary OC from both fossil-fuel and non-fossil emissions.

Ground-based remote sensing measurements of nitrogen dioxide are compared to the Lotos-Euros air quality (AQ) model. Measurements were taken in the Netherlands with a UV-Vis spectrometer which observes scattered sunlight under different elevation viewing angles. On average, a surprisingly good agreement is found. Perhaps most striking is the agreement between model and observations as a function of wind direction. This demonstrates the quality of the AQ model and underlying emission inventory.

The chemical composition, sources, and evolution processes of PM1 were investigated with an Aerodyne ACSM during harvest seasons in the Yangtze River delta, China. Two biomass burning organic aerosol (BBOA) factors derived from PMF model were assessed. The oxidized BBOA contributes ~80% of the total BBOA loadings in the BB plumes. Evidence that BBOA may be oxidized to more aged and less volatile organics during the aging process was suggested.

The first set of studies illustrates that the liquid/liquid phase separation relative humidity (SRH) does not depend strongly on molecular weight. The second set of studies shows that for most particle types and temperature range studied, SRH does not depend strongly on temperature. SRH did depend strongly on temperature for particles containing α,4-dihydroxy-3-methoxybenzeneacetic acid mixed with ammonium bisulfate due to a combination of low temperature and low water content.

Canadian Arctic air samples were analysed for enantiomers (mirror-image isomers) of pesticides α-hexachlorocyclohexane (α-HCH), trans-chlordane (TC) and cis-chlordane (CC). Annual cycles of enantiomer proportions suggested greater emission of microbially degraded residues from water and soil in warm vs. cold seasons. Enantiomer profiles may change in the future with rising contributions from secondary sources, monitoring them could increase the forensic capability in air monitoring programs.

This study analyzed air and precipitation concentrations of 43 polycyclic aromatic compounds (PACs) collected in the Athabasca oil sands region. A database has been built for the parameter scavenging ratio, which is defined as the ratio of the concentration of PACs in precipitation to that in air. A better understanding of the potential differences between gas and particulate scavenging and between snow and rain scavenging has been achieved.

Emission inventories are a key component of simulating past, present and future climate. In this article we have evaluated three black carbon emission inventories for emissions of India using observations made from a strategic location. Annual average simulated black carbon concentration is found to be 35% to 60% lower than observed concentration because of underestimation of emissions of southern India in the inventories.

Immersion freezing measurements from seven different measurement techniques were intercompared using a biological ice nucleating material from bacteria. Although different techniques examined differently concentrated droplets, it was possible to find a uniform description, which showed that results from all experiments were generally in good agreement and were also in agreement with parameterizations published earlier in literature.

The ice nucleation scheme in the Community Atmosphere Model (CAM5) was improved by considering the effects of pre-existing ice crystals and some other modifications. Subsequently, the comparison between different ice nucleation parameterizations is investigated. Experiment using the ice nucleation parameterization of Kärcher et al. (2006) predicts a much smaller anthropogenic aerosol indirect forcing than that using the parameterizations of Liu and Penner (2005) and Barahona and Nenes (2009).

Using MOPITT (version 5) tropospheric profile and surface layer retrievals, we constrain global CO emissions in the period of June 2004 – May 2005. The inversions suggest a reduction in CO emission in the tropics and an increase in emissions at middle and high latitudes. The results demonstrate that the use of the surface layer retrievals from MOPITT can significantly mitigate the potential impacts of model bias in OH and long-range transport on CO emission estimates.

We describe the multi-stage approach applied in the GAINS model to assess compliance with PM10 limit values at more than 1850 individual air quality monitoring stations in Europe. We analyse source contributions to ambient concentrations and the implications of future policy choices on air quality for 2030. While current legislation does not solve compliance issues, problems are largely eliminated by EU-wide adoption of the best available emission control technology.