Seasonal and diurnal variations of atmospheric PAH concentrations between rural, suburban and urban areas

Abstract. Ultrafine Particles (UFP) can display sharp gradients in their number concentrations in urban environment due to their transient nature and rapid atmospheric processing. The ability of using air pollution data generated at a central monitoring station to assess exposure relies on our understanding of the spatial variability of a specific pollutant associated with a region. High spatial variation in the concentrations of air pollutants has been reported at scales of 10s of km for areas affected by primary emissions. Spatial variability in particle number concentrations (PNC) and size distributions needs to be investigated, as the representativeness of a monitoring station in a region is premised on the assumption of homogeneity in both of these metrics. This study was conducted at six sites, one in downtown Los Angeles and five located about 40–115 km downwind in the receptor areas of Los Angeles air basin. PNC and size distribution were measured using Condensation Particle Counters (CPC) and Scanning Mobility Particle Sizer (SMPS). The seasonal and diurnal variations of PNC implied that PNC might vary significantly with meteorological conditions, even though the general patterns at the sites may remain generally similar across the year due to consistency of sources around them. Regionally transported particulate matter (PM) from upwind urban areas of Los Angeles lowered spatial variation by acting as a "homogenizing" factor during favorable meteorological conditions. Spatial variability also increased during hours of the day during which the effects of local sources predominate. The spatial variability associated with PNC (quantified using Coefficients of Divergence, CODs), averaged about 0.3, which was generally lower than that based on specific size ranges. Results showed an inverse relationship of COD with particles size, with fairly uniform values in the particle range which is associated with regional transport. Our results suggest that spatial variability, even in the receptor regions of Los Angeles Basin, should be assessed for both PNC and size distributions, and should be interpreted in context of seasonal and diurnal influences, and suitably factored if values for exposure are ascertained using a central monitoring station.

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Mars Global Ionosphere-Thermosphere Model: Solar cycle, seasonal, and diurnal variations of the Mars upper atmosphere

Journal of Geophysical Research Planets ◽

10.1002/2014je004715 ◽

2015 ◽

Vol 120 (2) ◽

pp. 311-342 ◽

Cited By ~ 93

Author(s):

S. W. Bougher ◽

D. Pawlowski ◽

J. M. Bell ◽

S. Nelli ◽

T. McDunn ◽

...

Keyword(s):

Solar Cycle ◽

Diurnal Variations ◽

Upper Atmosphere ◽

Seasonal And Diurnal Variations

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Seasonal and diurnal variations in moisture, heat and CO2 fluxes over a typical steppe prairie in Inner Mongolia, China

Hydrology and Earth System Sciences ◽

10.5194/hess-13-987-2009 ◽

2009 ◽

Vol 13 (7) ◽

pp. 987-998 ◽

Cited By ~ 15

Author(s):

Z. Gao ◽

D. H. Lenschow ◽

Z. He ◽

M. Zhou

Keyword(s):

Inner Mongolia ◽

Surface Albedo ◽

Sensible Heat Flux ◽

Experimental Period ◽

Diurnal Variations ◽

Heat Fluxes ◽

Co2 Fluxes ◽

Sensible Heat ◽

Eddy Covariance Method ◽

Seasonal And Diurnal Variations

Abstract. In order to examine energy partitioning and CO2 exchange over a steppe prairie in Inner Mongolia, China, fluxes of moisture, heat and CO2 in the surface layer from June 2007 through June 2008 were calculated using the eddy covariance method. The study site was homogenous and approximately 1500 m×1500 m in size. Seasonal and diurnal variations in radiation components, energy components and CO2 fluxes are examined. Results show that all four radiation components changed seasonally, resulting in a seasonal variation in net radiation. The radiation components also changed diurnally. Winter surface albedo was higher than summer surface albedo because during winter the snow-covered surface increased the surface albedo. The seasonal variations in both sensible heat and CO2 fluxes were stronger than those of latent heat and soil heat fluxes. Sensible heat flux was the main consumer of available energy for the entire experimental period. The energy imbalance problem was encountered and the causes are analyzed.

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Characteristics of wintertime VOCs in suburban and urban Beijing: concentrations, emission ratios, and festival effects

10.5194/acp-2018-1260 ◽

2019 ◽

Author(s):

Kun Li ◽

Junling Li ◽

Shengrui Tong ◽

Weigang Wang ◽

Ru-Jin Huang ◽

...

Keyword(s):

Atmospheric Chemistry ◽

Urban Areas ◽

Diurnal Variations ◽

Urban Site ◽

Anthropogenic Emissions ◽

Suburban Areas ◽

Key Characteristics ◽

Volatile Organic ◽

Suburban Site ◽

Emission Ratios

Abstract. Measurements of volatile organic compounds (VOCs) were performed at a suburban site and an urban site in Beijing during the winter of 2014–2015. The VOC concentrations and emission ratios (ERs) to CO were compared at these two sites. It is found that though the VOC concentrations at the urban site are 2.67 ± 1.15 times of those at the suburban site, the ERs are similar (within a factor of 1.5). It is indicated that: (1) the VOCs at suburban areas are mainly from the transportation from the urban areas; (2) the ERs measured at the urban areas are also valid for the surrounding suburban areas. By comparing the diurnal variations and the contribution of anthropogenic emissions at both sites, we find that the photochemical processes are very active at the urban site, and these processes play an important role in the daytime oxygenated VOCs (OVOCs) formation. The methanol at the urban site and the formic acid at the suburban site probably have additional sources, which are attributed to be solvent use and soil/agriculture, respectively. The festival effects from Chinese New Year (CNY) were investigated. The VOC concentrations decreased ~ 60 % during CNY holidays, probably due to the population migration during festival holidays. In addition, fireworks are found to be an important source of acetonitrile, aromatics, and some OVOCs during CNY festival, and should be controlled more strictly. This study provides key characteristics of wintertime VOCs in suburban and urban Beijing, and has implications for better understanding the atmospheric chemistry of VOCs in and around this megacity.

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SEASONAL AND DIURNAL VARIATIONS IN THE OSMOTIC VALUES AND SUCTION TENSION VALUES IN THE AERIAL PORTIONS OF AMBROSIA TRIFIDA

American Journal of Botany ◽

10.1002/j.1537-2197.1933.tb08870.x ◽

1933 ◽

Vol 20 (1) ◽

pp. 18-34 ◽

Cited By ~ 9

Author(s):

Ervin M. Herrick

Keyword(s):

Diurnal Variations ◽

Ambrosia Trifida ◽

Seasonal And Diurnal Variations

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Seasonal and Diurnal Variations in the Priestley–Taylor Coefficient for a Large Ephemeral Lake

Water ◽

10.3390/w12030849 ◽

2020 ◽

Vol 12 (3) ◽

pp. 849 ◽

Cited By ~ 1

Author(s):

Guojing Gan ◽

Yuanbo Liu ◽

Xin Pan ◽

Xiaosong Zhao ◽

Mei Li ◽

...

Keyword(s):

Poyang Lake ◽

High Water ◽

Diurnal Variations ◽

Observation Data ◽

Available Energy ◽

Diurnal Patterns ◽

Ephemeral Lakes ◽

Seasonal And Diurnal Variations ◽

Daily Scale ◽

Mean Square Errors

The Priestley–Taylor equation (PTE) is widely used with its sole parameter (α) set as 1.26 for estimating the evapotranspiration (ET) of water bodies. However, variations in α may be large for ephemeral lakes. Poyang Lake, which is the largest freshwater lake in China, is water-covered and wetland-covered during its high-water and low-water periods, respectively, over a year. This paper examines the seasonal and diurnal variations in α using eddy covariance observation data for Poyang Lake. The results show that α = 1.26 is overall feasible for both periods at daily and subdaily scales. No obvious seasonal trend was observed, although the standard deviation in α for the wetland was larger than that for the water surface. The mean bias in evaporation estimations using the PTE was less than 5 W·m−2 during both periods, and the root mean square errors were much smaller than the average evaporation measurements at daily scale. U-shaped diurnal patterns of α were found during both periods, due partly to the negative correlation between α and the available energy (A). Compared to the vapor pressure deficit (VPD), wind speed (u) exerts a larger contribution to these variations. In addition, u is positively correlated with α during both periods, however, VPD was positively and negatively correlated with α during the high-water and low-water periods, respectively. Subdaily α exhibited contrasting clusters in the (u, VPD) plane under the same available energy ranges. Our study highlights the seasonal and diurnal course of α and suggests the careful use of PTE at subdaily scales.

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