Metallic corrosion in the polluted urban atmosphere of Hong Kong.

This study aimed to explore the relationship between air pollutants, particularly acidic particles, and metallic material corrosion. An atmospheric corrosion test was carried out in spring-summer 2012 at a polluted urban site, i.e., Tung Chung in western Hong Kong. Nine types of metallic materials, namely iron, Q235 steel, 20# steel, 16Mn steel, copper, bronze, brass, aluminum, and aluminum alloy, were selected as specimens for corrosion tests. Ten sets of the nine materials were all exposed to ambient air, and then each set was collected individually after exposure to ambient air for consecutive 6, 13, 20, 27, 35, 42, 49, 56, 63, and 70 days, respectively. After the removal of the corrosion products on the surface of the exposed specimens, the corrosion rate of each material was determined. The surface structure of materials was observed using scanning electron microscopy (SEM) before and after the corrosion tests. Environmental factors including temperature, relative humidity, concentrations of gaseous pollutants, i.e., sulfur dioxide (SO2), nitrogen dioxide (NO2), carbon monoxide (CO), ozone (O3), and particulate-phase pollutants, i.e., PM2.5 (FSP) and PM10 (RSP), were monitored. Correlation analysis between environmental factors and corrosion rate of materials indicated that iron and carbon steel were damaged by both gaseous pollutants (SO2 and NO2) and particles. Copper and copper alloys were mainly corroded by gaseous pollutants (SO2 and O3), while corrosion of aluminum and aluminum alloy was mainly attributed to NO2 and particles.

Tracer-based source apportionment of polycyclic aromatic hydrocarbons in PM2.5 in Guangzhou, southern China, using positive matrix factorization (PMF).

From 28 November to 23 December 2009, 24-h PM2.5 samples were collected simultaneously at six sites in Guangzhou. Concentrations of 18 polycyclic aromatic hydrocarbons (PAHs) together with certain molecular tracers for vehicular emissions (i.e., hopanes and elemental carbon), coal combustion (i.e., picene), and biomass burning (i.e., levoglucosan) were determined. Positive matrix factorization (PMF) receptor model combined with tracer data was applied to explore the source contributions to PAHs. Three sources were identified by both inspecting the dominant tracer(s) in each factor and comparing source profiles derived from PMF with determined profiles in Guangzhou or in the Pearl River Delta region. The three sources identified were vehicular emissions (VE), biomass burning (BB), and coal combustion (CC), accounting for 11 ± 2%, 31 ± 4%, and 58 ± 4% of the total PAHs, respectively. CC replaced VE to become the most important source of PAHs in Guangzhou, reflecting the effective control of VE in recent years. The three sources had different contributions to PAHs with different ring sizes, with higher BB contributions (75 ± 3%) to four-ring PAHs such as pyrene and higher CC contributions (57 ± 4%) to six-ring PAHs such as benzo[ghi]perylene. Temporal variations of VE and CC contributions were probably caused by the change of weather conditions, while temporal variations of BB contributions were additionally influenced by the fluctuation of BB emissions. Source contributions also showed some spatial variations, probably due to the source emission variations near the sampling sites.

Polycyclic aromatic hydrocarbons in PM2.5 in Guangzhou, southern China: spatiotemporal patterns and emission sources.

Fine particulate samples were simultaneously collected at six sites in Guangzhou in November-December 2009. Eighteen polycyclic aromatic hydrocarbons (PAHs) and tracers, i.e. hopanes, elemental carbon, picene and levoglucosan were measured. Three high level episodes were observed during the sampling period, likely due to accumulation effects. Back trajectory analysis revealed that the air masses for the three episodes were from eastern inland Pearl River Delta (PRD) region. There was no obvious concentration gradient for total and 5-6 ring PAHs such as benzo[g,h,i]perylene (BghiP) from urban to rural sites. However, 4-ring PAHs such as pyrene (Pyr) exhibited significantly higher levels at rural site than that at urban/suburban sites (p<0.01). BghiP correlated well with hopanes, elemental carbon and picene, indicating vehicular emissions and coal combustion were the sources of 5-6 ring PAHs, which were further confirmed by comparing the four tracers/BghiP ratios and IcdP/BghiP ratios in ambient samples with those from source profiles. Results indicated that vehicular emissions were no longer the dominant sources in winter season in Guangzhou.