As the world’s largest grain producer, China’s straw yield was 700 million tonnes in 2014. With a national utilization rate of 80% in 2015, there is still a large amount of straw burned in open-field, resulting in air pollution and a reduction in the quantity available as a source of bioenergy. This paper conducts a literature review of success stories and major challenges in comprehensive straw utilization in and out of China. It is noted that nationwide long-term feasible and sustainable straw utilization at a high rate is a highly complex operation, involving most societal sectors, many people and facilities often at different regions. Scenarios were analyzed to estimate the energy potential and air emission reductions China would accomplish in 2020 by converting an additional 5 or 10% of straw-yield to biofuel. Currently, the approach to control straw burning in China is primarily administrative, relying heavily on prohibition and penalties, inconsistent across policy areas and geography, and lacking in long-term planning. Consequently, the effectiveness of the current approach is limited. The main cause of burning is a lack of infrastructure, effective preventive measures, and viable alternatives. Recommendations aimed at promoting a circular bio-economy around using crop straw as resources were provided, including improving straw utilization rates and reducing open-field burning.

Atmospheric mercury (Hg) measurements from across Canada were compiled and analysed as part of a national Hg science assessment. Here we update long-term trends of Hg in air and precipitation, and present more extensive measurements on patterns and trends in speciated Hg species (gaseous elemental mercury—GEM, reactive gaseous mercury—RGM, and total particulate mercury on particles <2.5 μm—TPM_2.5) at several sites. A spatial analysis across Canada revealed higher air concentrations and wet deposition of Hg in the vicinity of local and regional emission sources, and lower air concentrations of Hg at mid-latitude maritime sites compared to continental sites. Diel and seasonal patterns in atmospheric GEM, RGM and TPM_2.5 concentrations reflected differences in patterns of anthropogenic emissions, photo-induced surface emissions, chemistry, deposition and mixing. Concentrations of GEM decreased at rates ranging from −0.9% to −3.3% per year at all sites where measurements began in the 1990s. Concentrations of total Hg in precipitation declined up to 3.7% yr⁻¹. Trends in RGM and TPM_2.5 were less clear due to shorter measurement periods and low concentrations, however, in spring at the high Arctic site (Alert) when RGM and TPM_2.5 concentrations were high, concentrations of both increased by 7%–10% per year.

Spatial monitoring campaigns of volatile organic compounds were carried out in two similarly sized urban industrial cities, Windsor and Sarnia, ON, Canada. For Windsor, data were obtained for all four seasons at approximately 50 sites in each season (winter, spring, summer, and fall) over a three-year period (2004, 2005, and 2006) for a total of 12 sampling sessions. Sampling in Sarnia took place at 37 monitoring sites in fall 2005. In both cities, passive sampling was done using 3M 3500 organic vapor samplers. This paper characterizes benzene, toluene, ethylbenzene,o, and (m+p)-xylene (BTEX) concentrations and relationships among BTEX species in the two cities during the fall sampling periods. BTEX concentration levels and rank order among the species were similar between the two cities. In Sarnia, the relationships between the BTEX species varied depending on location. Correlation analysis between land use and concentration ratios showed a strong influence from local industries. Use one of the ratios between the BTEX species to diagnose photochemical age may be biased due to point source emissions, for example, 53 tonnes of benzene and 86 tonnes of toluene in Sarnia. However, considering multiple ratios leads to better conclusions regarding photochemical aging. Ratios obtained in the sampling campaigns showed significant deviation from those obtained at central monitoring stations, with less difference in the (m+p)/E ratio but better overall agreement in Windsor than in Sarnia.

Exposure to fine particulate matter (PM) results in adverse health outcomes. Although this is a global concern, residents of China may be particularly vulnerable due to frequent severe air pollution episodes associated with economic growth, industrialization, and urbanization. Until 2012, PM_2.5 was not regulated and monitored in China and annual average concentrations far exceeded the World Health Organizations guidelines of 10 μg/m³. Since the establishment of PM_2.5 Ambient Air Quality Criteria in 2012, concentrations have decreased, but still pose significant health risks. A review of ambient PM_2.5 health effect studies is warranted to evaluate the current state of knowledge and to prioritize future research efforts. Our review found that recent literature has confirmed associations between PM_2.5 exposure and total mortality, cardiovascular mortality, respiratory mortality, hypertension, lung cancer, influenza and other adverse health outcomes. Future studies should take a long-term approach to verify associations between exposure to PM_2.5 and health effects. In order to obtain adequate exposure assessment at finer spatial resolutions, high density sampling, satellite remote sensing, or models should be employed. Personal monitoring should also be conducted to validate the use of outdoor concentrations as proxies for exposure. More research efforts should be devoted to seasonal patterns, sub-population susceptibility, and the mechanism by which exposure causes health effects. Submicron and ultrafine PM should also be monitored and regulated.

This study investigates temporal variations and long-term (1996–2015) trends of ground-level O₃ (ozone) and its precursors, NO_x (nitrogen oxides), and volatile organic compounds in Windsor, Ontario, Canada. During the 20-year study period, NO_x, non-methane hydrocarbon concentrations, and ozone formation potential decreased significantly by 58 %, 61 %, and 73 %, respectively, while O₃ concentrations increased by 33 % (20.3 ppb in 1996 vs. 27 ppb in 2015). Our analysis revealed that the increased annual O₃ concentrations in Windsor were due to (1) decreased O₃ titration (by 50 % between 1996 and 2015) owing to declining nitric oxide concentrations, which is suggested by a slightly decreasing trend of annual mean total O₃ concentrations after the titration effect is removed, (2) reduced local photochemical production of O₃ because of dwindling precursor emissions, and (3) an increased background O₃ level that has a greater impact on the low-to-median concentrations. The net effect of those factors is decreasing peak O₃ levels during the smog season from May to September but an overall increasing trend of annual means. These results indicate that the emission control measures are effective in reducing peak ozone concentrations. However, challenges in lowering annual O₃ levels call for long-term collaborative efforts in the region and around the globe.