Climatology of Ozone, PAN, CO, and NMHC in the Free Troposphere Over the Southern North Atlantic

Free tropospheric measurements of ozone, peroxyacetylnitrate andprecursors (CO, NMHC) that were made within the framework of the EUROTRACsub-project TOR (Tropospheric Ozone Research) between 1990 and 1995 at theGAW station Izana, Tenerife (28°18N, 16°30W) arediscussed. The average annual cycles reveal the importance of transport fromnorthern mid-latitudes and the role of photo-chemistry. According toair-mass trajectories, which were supplied to us from AEROCE(Atmosphere/Ocean Chemistry Experiment), transport from northernmid-latitudes is associated with high precursor concentrations in winter,whereas ozone concentrations in winter are not much influenced by transportpatterns, suggesting a rather uniform distribution over the northern part ofthe Northern Hemisphere around mean value of 43 ± 5 ppb. In summer,high ozone concentrations of up to 90 ppb are often encountered duringtransport from north, while the levels of precursors are much lower than inwinter, because of photochemical destruction. Trajectories from southerlylatitudes and the Sahara usually have the lowest ozone concentrationsassociated with them.     

Influence of air masses on particle number concentration and size distribution at Mt. Waliguan, Qinghai Province, China

Particle size distribution of 12–500 nm was measured at Mt. Waliguan, China Global Atmosphere Watch Baseline Observatory, from Aug. in 2005 to May in 2007. 72-hr back-trajectories at 100-m arrival height above ground level for the same period were calculated at 6:00, 12:00, and 21:00 (Beijing Time) for each day using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT-4) model developed by NOAA/ARL. It was found that air mass sources significantly impact particle number concentration and size distribution at Mt. Waliguan. Cluster analysis of back-trajectories show that higher Aitken mode particle number concentration was observed when air masses came from or passed by the northeastern section of Mt. Waliguan, with short trajectory length. High number concentration of nucleation mode was associated with air masses from clean regions, with long trajectory length     

The August 2007 Heat Wave in North Carolina: Meteorological Factors and Local Variability

August 2007 was an exceptionally warm month across North Carolina. Hundreds of daily maximum and daily high minimum temperature records, as well as numerous all-time temperature records, were either tied or broken during the month. At the same time, a drought of historic proportions overspread much of the Southeast United States. A critical aspect of the August 2007 heat wave was the observed variability in heat and humidity across the different geographic regions of North Carolina. The highest maximum temperatures occurred most frequently in the Piedmont and Sandhills regions, while minimum temperatures were exceptionally high along the coast. The broad-scale pattern of heat can be tied to adiabatic warming associated with subsidence downstream of a persistent upper-level ridge centered over the Mississippi River Valley. Regional to local variations in the heat and humidity across North Carolina are linked to upwind sensible heat fluxes associated with major soil moisture deficits, adiabatic warming connected with downsloping winds off the Appalachian Mountains, and the depth of the mixing layer. Along the coast, the pattern of heat and humidity was tied to the positioning of a mesoscale thermal trough and the presence and strength of the sea-breeze circulation.     

兰州春季沙尘过程PM10输送路径及其潜在源区

将2001-2008年分为沙尘天气相对多年和相对少年,计算兰州市春季逐日4个时次的4d气团后向轨迹。通过聚类分析得到春季到达兰州市区的主要气团轨迹组,结合可吸入颗粒物PM10日均质量浓度资料,通过计算潜在源贡献因子PSCF（potential source contribution function）和浓度权重轨迹CWT（concentration-weighted trajectory）,得到影响兰州市春季PMlo质量浓度的潜在源区以及不同源区对兰州市春季PM10质量浓度贡献的差异。结果表明,在沙尘天气相对多年,西路径和西北路径发生比例最高,分别占总轨迹的33％和19．4％,其中有50％以上为污染轨迹,是造成兰州市春季高质量浓度PM10污染的主要输送路径。沙尘天气相对少年的主要输送路径是西路径,其次是北路径,分别占23．6％和18％。影响兰州市春季大气PM10质量浓度的潜在源区分布在新疆塔里木盆地、吐鲁番盆地、青海柴达木盆地、甘肃河西走廊、内蒙古中部和西部的沙漠戈壁地区。     

Rainfall chemistry: long range transport versus below cloud scavenging. A two-year study at an inland station (Opme, France)

The present study investigates the chemical composition of wet atmospheric precipitation samples on a daily and an intra-event timescales in Opme, an experimental meteorological station located near Clermont-Ferrand, France. The samples have been collected from November 2005 to October 2007. A total of 217 rainwater samples, integrated for 24 h, were collected and analyzed for pH, conductivity, Na⁺, K⁺, Mg²⁺, NH₄⁺, Ca²⁺, Cl⁻, NO₃⁻ , SO₄²⁻ , PO₄³⁻ and HCO₃⁻. The composition of the rainwater collected appeared to be controlled by the following potential sources: neutralisation process (association among calcium, ammonium with nitrate and sulphate), marine and terrestrial sources. In order to determine the role of long-range transport, the integrated events were classified according to four origins of air-masses: (1) West, (2) North and East, (3) South including Iberian and Italian Peninsulae and (4) local. This analysis allows identifying the source areas of the different association of elements defined. Although calcium is always dominant, total content of rainfall is variable and neutralisation process can be more or less efficient and specific. Rainout (long-range transport) and washout (below-cloud scavenging) were investigated through intra-event measurements of chemical species. Four rain-events have been selected according to the four classes of origins of air-masses. It appears that the first fractions are responsible for an important part of the chemical content of the whole event. Terrestrial species, locally emitted, induce the neutralisation process of acid species. Local meteorological conditions, such as wind’s speed and direction, play an important role as they could provoke recharges of the below cloud air column during the event.     

兰州春季沙尘过程PM10输送路径及其潜在源区

将2001-2008年分为沙尘天气相对多年和相对少年,计算兰州市春季逐日4个时次的4 d气团后向轨迹。通过聚类分析得到春季到达兰州市区的主要气团轨迹组,结合可吸入颗粒物PM₁₀日均质量浓度资料,通过计算潜在源贡献因子PSCF(potential source contribution function)和浓度权重轨迹CWT(concentration-weighted trajectory),得到影响兰州市春季PM₁₀质量浓度的潜在源区以及不同源区对兰州市春季PM₁₀质量浓度贡献的差异。结果表明,在沙尘天气相对多年,西路径和西北路径发生比例最高,分别占总轨迹的33%和19.4%,其中有50%以上为污染轨迹,是造成兰州市春季高质量浓度PM₁₀污染的主要输送路径。沙尘天气相对少年的主要输送路径是西路径,其次是北路径,分别占23.6%和18%。影响兰州市春季大气PM₁₀质量浓度的潜在源区分布在新疆塔里木盆地、吐鲁番盆地、青海柴达木盆地、甘肃河西走廊、内蒙古中部和西部的沙漠戈壁地区。