Publications

This study investigates the chemical composition of PM2.5 collected at a central location in Beijing, China, during winter 2016 and summer 2017. The samples were characterised using direct-infusion negative-nano-electrospray-ionisation ultrahigh-resolution mass spectrometry to elucidate the composition and the potential primary and secondary sources of the organic fraction. The samples from the two seasons were compared with those from a road-tunnel site and an urban background site in Birmingham, UK, analysed in the course of an earlier study using the same method. There were strong differences in aerosol particle composition between the seasons, particularly regarding (poly-)aromatic compounds, which were strongly enhanced in winter, likely due to increased fossil fuel and biomass burning for heating. In addition to the seasonal differences, compositional differences between high- and low-pollution conditions were observed, with the contribution of sulfur-containing organic compounds strongly enhanced under high-pollution conditions. There was a correlation of the number of sulfur-containing molecular formulae with the concentration of particulate sulfate, consistent with a particle-phase formation process.

This study aims to use dispersion-modeled concentrations of nitrogen oxides (NOx)
and black carbon (BC) to estimate bicyclist exposures along a network of roads and bicycle paths.
Such modeling was also performed in a scenario with increased bicycling. Accumulated concentrations
between home and work were thereafter calculated for both bicyclists and drivers of cars. A transport
model was used to estimate trac volumes and current commuting preferences in Stockholm County.
The study used individuals’ home and work addresses, their age, sex, and an empirical model
estimate of their expected physical capacity in order to establish realistic bicycle travel distances. If car
commuters with estimated physical capacity to bicycle to their workplace within 30 min changed
their mode of transport to bicycle, >110,000 additional bicyclists would be achieved. Time-weighted
mean concentrations along paths were, among current bicyclists, reduced from 25.8 to 24.2 µg/m3 for
NOx and 1.14 to 1.08 µg/m3 for BC. Among the additional bicyclists, the yearly mean NOx dose from
commuting increased from 0.08 to 1.03 µg/m3. This would be expected to yearly cause 0.10 fewer
deaths for current bicycling levels and 1.7 more deaths for additional bicycling. This increased air
pollution impact is much smaller than the decrease in the total population.

In the central Arctic Ocean the formation of clouds and their properties are sensitive to the availability of cloud condensation nuclei (CCN). The vapors responsible for new particle formation (NPF), potentially leading to CCN, have remained unidentified since the first aerosol measurements in 1991. Here, we report that all the observed NPF events from the Arctic Ocean 2018 expedition are driven by iodic acid with little contribution from sulfuric acid. Iodic acid largely explains the growth of ultrafine particles (UFP) in most events. The iodic acid concentration increases significantly from summer towards autumn, possibly linked to the ocean freeze-up and a seasonal rise in ozone. This leads to a one order of magnitude higher UFP concentration in autumn. Measurements of cloud residuals suggest that particles smaller than 30 nm in diameter can activate as CCN. Therefore, iodine NPF has the potential to influence cloud properties over the Arctic Ocean.