Particulate organic nitrates at Mount Tai in winter and spring: Variation characteristics and effects of mountain-valley breezes and elevated emission sources.

Particulate organic nitrates, among the major components of secondary organic aerosols and fine particles, play important roles in regional nitrogen cycle, ozone budget, and cloud condensation nuclei formation. However, the pollution characteristics of particulate organic nitrates at mountain areas and the effects of anthropogenic pollutant transport remain poorly understood. In this study, field sampling and measurements were conducted at a high-elevation mountain site over North China Plain in winter and spring. Total five kinds of particulate organic nitrates in fine particles were determined by ultra-high performance liquid chromatography-electrospray mass spectrometry. The average total concentrations of particulate organic nitrates were 330 ± 121 ng m-3 and 247 ± 63 ng m-3 in winter and spring. The monoterpene-derived organic nitrates were the dominant components in both seasons with their contribution higher than 70%, accounting for 1.2 ± 0.8% and 2.0 ± 1.0% in organic aerosols in winter and spring, respectively. The significantly higher levels of particulate organic nitrates in winter than spring was ascribed to the strong effects of mountain-valley breezes and coal combustion plumes. The increasing concentrations of NOx and particulate matters brought by the valley breeze at daytime facilitated the formation of MHN215, OAKN359, and OAHN361, while the rising SO2 abundance and the sulfate aerosols transported by elevated emission sources affected the formation of MDCN247 at nighttime.

Changed mercury speciation in clouds driven by changing cloud water chemistry and impacts on photoreduction: Field evidence at Mt. Tai in eastern China.

Chemical speciation of mercury (Hg) in clouds largely determines the photochemistry of Hg in the atmosphere and consequently influences Hg deposition on the surface through precipitation. Cloud water chemistry has notably changed over the last decade in response to global changes, however, the effects on Hg speciation remain poorly understood. During summer 2021, we collected sixty cloud water samples at Mt. Tai in eastern China and compared the cloud chemistry and Hg speciation with our previous findings during summer 2015. The results showed that although there were no statistically significant differences in the concentrations of total Hg (THg), dissolved Hg (DHg), and particulate Hg (PHg), there was a distinct shift in DHg species from the predominated Hg-DOM (78.6% in 2015 campaign) to the more homogeneously distributed Hg(OH)2 (28.4% in 2021 campaign), HgBr2 (26.5%), Hg-DOM (17.3%) and HgBrOH (17.0%). Changes in cloud water chemistry, particularly the significant increase in pH values to 6.49 ± 0.27 and unexpectedly high levels of bromide ions (Br-, 0.19 ± 0.22 mg L-1), were found to drive the changing of Hg speciation by enhancing Hg(II) hydrolysis and binding by Br-. Elevated Br- originating primarily from the continent likely caused noticeable differences in the dominating DHg species between cloud water sourced from marine and continental regions. The changes in chemical speciation of DHg were estimated to result in a 2.6-fold decrease in Hg(II) photoreduction rate between 2015 and 2021 campaigns (0.178 ± 0.054 h-1 vs. 0.067 ± 0.027 h-1), implying a shortened lifetime of atmospheric Hg and increased ecological risks associated with Hg wet deposition.

[Long-term Trends and Sources of Atmospheric Halocarbons at Mount Taishan, Northern China].

Halocarbons are hot topics in atmospheric environment and climate change research. Combining observational data from six field campaigns at the summit of Mount Taishan (36.25°N, 117.10°E, 1534 m above sea level) with backward trajectory and receptor source analyses, this study analyzed the long-term trends and major emission sources of halocarbons in the regional background atmosphere of the North China Plain (NCP) from 2003 to 2018. The results showed that the volume fraction of species eliminated by the Montreal Protocol (MP) showed a significant downward trend; however, the MP-controlled and unregulated species showed an overall upward trend. Meanwhile, the median volume fraction of the MP-controlled and unregulated species at Mount Taishan were significantly higher than the mid-latitude median background values in the northern hemisphere. Mount Taishan air was mainly affected by four types of air masses, of which the air mass originating from NCP accounted for the highest proportion (41%). The major sources of halocarbons were biomass/biofuel burning (38.1%), refrigeration (26.2%), industrial and domestic solvent use (21.7%), solvent use in the electronic industry (8.7%), and leakage of chlorofluorocarbon (CFCs) banks (5.3%). This study fully demonstrates that MP has been effectively implemented in China and provides evidence and recommendations to further reduce and control the volume fraction of halocarbons.