Chemical characteristics and sources of PM1 during the 2016 summer in Hangzhou.

During the 2016 Hangzhou G20 Summit, the chemical composition of submicron particles (PM1) was measured by a High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) along with a suite of collocated instruments. The campaign was undertaken between August 5 and September 23, 2016. The impacts of emission controls and meteorological conditions on PM1 chemical composition, diurnal cycles, organic aerosol (OA) source apportionment, size distribution and elemental ratios were characterized in detail. Excluding rainy days, the mean PM1 mass concentration during G20 was 30.3 µg/m3, similar to that observed before G20 (28.6 µg/m3), but much lower than that after G20 (42.7 µg/m3). The aerosol chemistry during the three periods was substantially different. Before G20, high PM1 loading mostly occurred at daytime, with OA accounting for 60.1% of PM1, followed by sulfate (15.6%) and ammonium (9.1%). During G20, the OA fraction decreased from 60.1% to 44.6%, whereas secondary inorganic aerosol (SIA) increased from 31.8% to 49.5%. After G20, SIA dominated high PM1 loading, especially at nighttime. Further analysis showed that the nighttime regional transport might play an unfavorable role in the slight increase of secondary PM1 during G20, while the strict emissions controls were implemented. The OA (O/C = 0.58) during G20 was more aged, 48.7% and 13.7% higher than that before and after G20 respectively. Our study highlighted that the emission controls during G20 were of great success in lowering locally produced aerosol and pollutants, despite of co-existence of nighttime regional transport containing aerosol high in low-volatile organics and sulfate. It was implied that not only are emissions controls on both local and regional scale important, but that the transport of pollutants needs to be sufficiently well accounted for, to ensure the successful implementation of air pollution mitigation campaigns in China.

Insights into the characteristics and sources of primary and secondary organic carbon: High time resolution observation in urban Shanghai.

There is growing evidence suggesting that organic aerosols play an important role in the evolution of severe haze episodes. However, long-term investigations of the different characteristics of carbonaceous aerosols during haze and non-haze days are insufficient. In this work, hourly measurements of organic carbon (OC) and elemental carbon (EC) in PM2.5 were conducted in Shanghai, a megacity in Eastern China, over the course of a year from July 2013 to June 2014. Both OC and EC exhibited a bimodal diel pattern and were highly dependent on the wind speed and direction. The concentration-weighted trajectory (CWT) analysis illustrated that primary OC (POC) and EC were largely associated with regional and long-range transport. Secondary OC (SOC) formation was the strongest during the harvest season owing to significant biomass burning emissions from the adjacent Yangtze River Delta and farther agricultural regions. Compared to OC (6.7 µg m-3) and EC (2.0 µg m-3) in the non-haze days, higher levels of both OC (15.6 µg m-3) and EC (7.7 µg m-3) were observed in the haze days as expected, but with lower OC/EC ratios in the haze days (2.4) than in non-haze days (4.6). The proportion of POC and EC in PM2.5 remained relatively constant as a function of PM2.5 mass loadings, while that of SOC significantly decreased on the highly polluted days. It is concluded that the haze pollution in urban Shanghai was influenced more by the primary emissions (POC and EC), while the role of SOC in triggering haze was limited.

Characteristics and origins of air pollutants in Wuhan, China, based on observations and hybrid receptor models.

To identify the characteristics of air pollutants and factors attributing to the formation of haze in Wuhan, this study analyzed the hourly observations of air pollutants (PM2.5, PM10, NO2, SO2, O3, and CO) from March 1, 2013, to February 28, 2014, and used hybrid receptor models for a case study. The results showed that the annual average concentrations for PM2.5, PM10, NO2, SO2, O3, and CO during the whole period were 89.6 µg m-3, 134.9 µg m-3, 54.9 µg m-3, 32.4 µg m-3, 62.3 µg m-3, and 1.1 mg m-3, respectively. The monthly variations revealed that the peak values of PM2.5, PM10, NO2, SO2, and CO occurred in December because of increased local emissions and severe weather conditions, while the lowest values occurred in July mainly due to larger precipitation. The maximum O3 concentrations occurred in warm seasons from May to August, which may be partly due to the high temperature and solar radiation. Diurnal analysis showed that hourly PM2.5, PM10, NO2, and CO concentrations had two ascending stages accompanying by the two traffic peaks. However, the O3 concentration variations were different with the highest concentration in the afternoon. A case study utilizing hybrid receptor models showed the significant impact of regional transport on the haze formation in Wuhan and revealed that the mainly potential polluted sources were located in the north and south of Wuhan, such as Baoding and Handan in Hebei province, and Changsha in Hunan province. IMPLICATIONS: Wuhan city requires a 5% reduction of the annual mean of PM2.5 concentration by the end of 2017. In order to accomplish this goal, Wuhan has adopted some measures to improve its air quality. This work has determined the main pollution sources that affect the formation of haze in Wuhan by transport. We showed that apart from the local emissions, north and south of Wuhan were the potential sources contributing to the high PM2.5 concentrations in Wuhan, such as Baoding and Handan in Hebei province, Zhumadian and Jiaozuo in Henan province, and Changsha and Zhuzhou in Hunan province.