Abstract. Data obtained in Hong Kong during the HongKong and the Pearl River Delta (PRD) Pilot Air Monitoring Study in autumn 2002 are analyzed to unravel the relationship between ground-level ozone (O 3 ), pollution precursors, and cross-border transport. Ten ozone episodes, during which the hourly O 3 concentration exceeded 100 ppbv in 9 cases and 90 ppbv in one case, are subject to detailed analysis, including one case with hourly O 3 of 203 ppbv, which is the highest concentration on record to date in Hong Kong. Combined with high-resolution back trajectories, dCO/dNO y (the ratio of enhancement of CO concentration above background to that of NO y ) is used to define whether O 3 is locally or regionally produced. Five out of the ten Hong Kong O 3 -episodes studied show a "pollution signature" that is indicative of impact from Guangdong Province. Examination of speciated volatile organic compounds (VOCs) shows that the reactivity of VOCs is dominated by anthropogenic VOCs, of which the reactive aromatics dominate, in particular xylenes and toluene. Calculations using a photochemical box model indicate that between 50-100% of the O 3 increase observed in Hong Kong during the O 3 episodes can be explained by photochemical generation within the Hong Kong area, provided that nitrous acid (HONO) is present at the concentrations derived from this study. An Observation-Based Model (OBM) is used to calculate the sensitivity of the O 3 production to changes in the concentrations of the precursor compounds. Generally the production of O 3 throughout much of the Hong Kong area is limited by VOCs, while high nitric oxide (NO) concentrations suppress O 3 concentration.

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Background and purpose Subjective memory impairment (SMI) and amnestic mild cognitive impairment (aMCI) are thought to represent the pre‐dementia stages of Alzheimer's disease (AD). SMI is considered a more advanced pre‐clinical status prior to aMCI. Understanding the neuromechanism of SMI will have great benefits for monitoring the disease progression of AD. The study aims to explore whether SMI shows alterations of white matter (WM) integrity similar to the patterns of aMCI. Methods The atlas‐based analyses were performed to investigate the diffusion changes in the major WM tracts amongst 22 individuals with normal cognition (NC), 22 SMI patients and 25 aMCI patients. The correlations between the altered diffusion metrics and cognitive performance in the SMI and aMCI groups were assessed. Results The diffusion tensor metrics of SMI were intermediate between the NC and aMCI groups. The aMCI group presented disrupted integrity in multiple WM tracts, including the left anterior thalamic radiation, right corticospinal tract and left cingulum of the hippocampus (CgH), compared to the NC group. The left CgH showed diffusion alterations in the SMI group. In the aMCI group, the mean diffusivity of the left CgH was negatively correlated with episodic memory, whilst the radial diffusivity of the right corticospinal tract was negatively correlated with executive function. No significant relationship was found in the SMI group. Conclusion The study suggested that SMI patients might present detectable WM integrity changes in the left CgH before exhibiting objective cognitive dysfunction, which may provide novel insights into the pathological mechanisms of AD.