Approaches for identifying PM2.5 source types and source areas at a remote background site of South China in spring

AbstractRice planthopper (RPH) populations of Nilaparvata lugens and Sogatella furcifera periodically have erupted across Asia. Predicting RPH population dynamics and identifying their source areas are crucial for the management of these migratory pests in China, but the origins of the migrants to temperate and subtropical regions in China remains unclear. In particular, their early migration to China in March and April have not yet been explored due to a lack of research data available from potential source areas, Central Vietnam and Laos. In this study, we examined the population dynamics and migratory paths of N. lugens and S. furcifera in Vietnam and South China in 2012 and 2013. Trajectory modeling showed that in March and April in 2012 and 2013, RPH emigrated from source areas in Central Vietnam where rice was maturing to the Red River Delta and South China. Early migrants originated from Southern Central Vietnam (14–16°N), but later most were from Northern Central Vietnam (16–19°N). Analysis of meteorological and light-trap data from Hepu in April (1977–2013) using generalized linear models showed that immigration increased with precipitation in Southern Central Vietnam in January, but declined with precipitation in Northern Central Vietnam in January. These results determined that the RPH originate from overwintering areas in Central Vietnam, but not from southernmost areas of Vietnam. Winter precipitation, rather than temperature was the most important factor determining the number of RPH migrants. Based on their similar population dynamics and low population densities in Central Vietnam, we further speculated that RPH migrate to track ephemeral food resources whilst simultaneously avoiding predators. Migrations do not seem to be initiated by interspecific competition, overcrowding or host deterioration. Nevertheless, S. furcifera establishes populations earlier than N. lugens South China, perhaps to compensate for interspecific competition. We provide new information that could assist with forecasting outbreaks and implementing control measures against these migratory pests.

Download Full-text

Seasonal variation of black carbon over the South China Sea and in various continental locations in South China

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-13-17375-2013 ◽

2013 ◽

Vol 13 (7) ◽

pp. 17375-17405 ◽

Cited By ~ 1

Author(s):

D. Wu ◽

C. Wu ◽

B. Liao ◽

F. Li ◽

H. Tan ◽

...

Keyword(s):

South China Sea ◽

South China ◽

Rainy Season ◽

Dry Season ◽

The South China Sea ◽

The South ◽

Monsoon Period ◽

China Sea ◽

Background Site ◽

Urban Sites

Abstract. Black carbon (BC) is an important atmospheric constitute as an air pollutant and as a climate forcer. To our knowledge, field measurements of BC have not been reported over the South China Sea. Observation of light absorption coefficients (σabs) and BC concentrations by Aethalometer were conducted on Yongxing Island in the South China Sea and at five continental sites in the Pearl River Delta (PRD) region, South China during the South China Sea monsoon period (rainy season, 16 May–20 June 2008) and the northeast monsoon period (dry season, 12 December 2008–8 January 2009). At the oceanic site, the daily average BC concentrations vary from 0.28 to 2.14 μg m−3 and seasonal variations of BC were small (0.67 in dry season and 0.54 μg m−3 in rainy season). Similarly, little seasonal difference was found at a background site in PRD (2.88 in dry season and 2.62 μg m−3 in rainy season). At PRD urban sites, the daily average concentration of BC ranges from 1.56 to 37.9 μg m−3, higher in the dry season (12.6 μg m−3) and lower in the rainy season (6.4 μg m−3). The observed average σabs values in rainy vs. dry seasons are 119 vs. 62 Mm−1 at the PRD urban sites, 29 vs. 26 Mm−1 at the PRD background site, and 8.4 vs. 7.2 Mm−1 at the marine site. A bi-peak pattern in diurnal BC variation was observed at all sites while this pattern is the most prominent at the urban sites. The first peak appears in the early morning rush hour and the second peak in early evening, with the evening peak more pronounced in dry season.

Download Full-text