Jianping Huang

Numerical simulation and process analysis of typhoon-related ozone episodes in Hong Kong

[1] In this study the synoptic patterns conducive to the occurrence of O 3 episodes in Hong Kong are categorized by an inspection of the weather charts over the period of 1999-2003. The synoptic patterns associated with tropical cyclones originating in the North Pacific Ocean and the South China Sea are found to be the most optimal weather conditions for the occurrence of ozone episodes in Hong Kong. A high-resolution version of the regional, three-dimensional, multiscale photochemical air quality model (Pollutants in the Atmosphere and Their Transport in Hong Kong (PATH)), developed by the Hong Kong Environmental Protection Department in 2000, has been employed to investigate the evolution of one type of ozone episode related to tropical cyclones. A nonhydrostatic meteorological model (MM5) was applied with four-dimensional data assimilation to provide necessary meteorological fields to the air quality model. The performances of both the meteorological and chemical models are evaluated by comparing the simulated results with the available observed data. An integrated process rate analysis is used to examine the relative contributions of individual physical and chemical processes in the formation of ozone episodes for obtaining a better understanding of the mechanisms of photochemical smog events in Hong Kong. Results show that about 30% of the total ozone production is due to local chemical production in the lower atmosphere boundary layer, and about 70% is contributed by interregional transport from southern China into Hong Kong. In addition, four main processes, including horizontal advection, vertical transport, photochemical reactions, and deposition are found to have a significant influence on the ground-level concentration of ozone. The sensitivity experiments indicate that the chemical regime for ozone formation in Hong Kong seems to be limited by volatile organic compounds.

Role of isoprene in secondary organic aerosol formation on a regional scale

The role of isoprene as a source of secondary organic aerosol (SOA) is studied using laboratory-derived SOA yields and the U.S. Environmental Protection Agency regional-scale Community Multiscale Air Quality (CMAQ) modeling system over a domain comprising the contiguous United States, southern Canada, and northern Mexico. Isoprene is predicted to be a significant source of biogenic SOA, leading to increases up to 3.8 μg m^(−3) in the planetary boundary layer (PBL, defined as 0–2.85 km) and 0.44 μg m^(−3) in the free troposphere over that in the absence of isoprene. While the addition of isoprene to the class of SOA-forming organics in CMAQ increases appreciably predicted fine-particle organic carbon (OC_(2.5)) in the eastern and southeastern U.S., total OC_(2.5) is still underpredicted in these regions. SOA formation is highly sensitive to the value of the enthalpy of vaporization of the SOA. The role of isoprene SOA is examined in a sensitivity study at values of 42 and 156 kJ mol^(−1); both are commonly used in 3-D aerosol models. Prediction of ambient levels of SOA in atmospheric models remains a challenging problem because of the importance of emissions inventories for SOA-forming organics, representation of gas phase atmospheric chemistry leading to semivolatile products, and treatment of the physics and chemistry of aerosol formation and removal.

Spatiotemporal characteristics of lake breezes over Lake Taihu, China

AbstractLake Taihu is a shallow lake located in the Yangtze River Delta region in East China. Lake breezes and their interactions with urban heat islands are of great importance to air quality and weather forecasting. In this study, surface observations at dense network and Lidar Wind Profiler measurements were utilized to characterize the lake breezes at Lake Taihu and assess the impact of geophysical factors on the development and intensity of the lake breezes. The lake breezes were characterized by a low occurrence frequency of 12 to 17% (defined as the percentage of days with lake breezes in a given month), weak speed (annual mean ranging from 1.5 to 3.3 m·s-1), late onset (average onset around 11:10 local standard time (LST), with a range of 09:00–13:00 LST), short duration (annual mean 3.5 hours), and low circulation depth (average depth of 400 m from 12:00–14:00 LST). The lake breezes were greatly suppressed when the geostrophic winds were higher than 4.1 m·s-1. The low heat capacity of shallow wat...