Analysis of the climatic mechanisms contributing to the summertime transport of lower atmospheric ozone across metropolitan Phoenix, Arizona, USA

Abstract

High concentrations of lower atmospheric ozone can adversely affect the health of humans, plants, and animals. Over the past decade, unhealthy levels of ozone across the Phoenix, Arizona (USA) urban area have been a focus of attention for the United States Environmental Protection Agency (EPA) and local government agencies. As ozone concentrations exceeding the standard set forth by the EPA occur in a preferred location within the Phoenix metropolitan area (eastern suburb of Mesa), it has become important to gain an understanding of the mechanisms that transport ozone within Phoenix and its suburbs. The objective of the study that is presented here was to examine the climatic factors that contributed to the spatial distribution of lower atmospheric ozone across the eastern portion of the Phoenix metropolitan area in mid-to-late summer 1998. Microclimatic and synopticscale atmospheric contributors were linked to the mesoscale transport of ozone. Forty-three study days were stratified into 3 categories: high ozone days (exceeded the EPA standard), moderate ozone days (approached the EPA standard), and low ozone days. Eleven days of high ozone were differentiated from the days of the remaining 2 categories by an atmosphere containing less water vapor, and therefore a greater surface receipt of insolation. This is not surprising given the fact that ozone production is a photochemical process. However, the movement of the lower atmospheric ozone is also an important issue. The results of the study suggest that the drier atmosphere and resultant high insolation at the surface were associated with a proximal area of high pressure aloft. Taken together, the result was warmer ground surface and overlying air temperatures, light winds, an apparent lack of turbulent lower atmospheric mixing, and light southwesterly winds at 850 mb that advected little moisture into the area. Associated with the light synoptic flow and warm surface condition on days of high ozone was a wind regime that appears to be the product of a mesoscale thermodynamic circulation. The daytime flow on high ozone days became directed upslope toward the higher elevations of the eastern Phoenix Valley. Embedded within the flow was a plume of high ozone concentrations that extended from an urban area of high ground traffic eastward into the eastern suburb of Mesa. Conversely, moderate and low ozone days were associated with an eastward displacement of high pressure aloft, greater advection of lowlevel moisture from the south and southeast, smaller insolation receipt, less surface heating, and a much less organized movement of lower atmospheric ozone than on high ozone days.

Nitrogen Transport and Retention in an Arid Land Watershed: Influence of Storm Characteristics on Terrestrial–aquatic Linkages

“…The observed difference in inorganic N concentration in rain and runoff between summer and winter is likely related to differences in storm intensity among seasons, as well as N input associated with dust storms, lightning fixation of N 2 during summer monsoons (Ridley et al 1996), or photochemical smog that moves into the study area from the Phoenix metropolitan area (Ellis et al 2000;Fernando et al 2001;Fenn et al 2003;Lee et al 2003). Summer storms are more likely to generate rapid overland flow (Canton et al 2001;Michaelides and Wainwright 2002) and facilitate fluvial export of N to the aquatic component of the watershed.…”

Atmospheric Particulate Pollutants and their Relationship with Meteorology in Ahmedabad

“…Surrounding topography restricts the transport of pollution away from the urban area. When a weak background synoptic circulation combines with a valley air temperature inversion and surrounding orographic blockade, the result is often a lack of dispersion of significant lower atmospheric pollutants away from the urban center (Berman et al, 1995;Lu and Turco 1995;Ellis et al, 2000). As far as the topography of Ahmedabad is concerned, the ground rises away from the city on all sides bounded by the gently sloping beautiful terrain.…”

Ozone Level Assessment on the Boukornine National Park (Tunisia) using Plant Biomonitoring: Influence of Altitudinal Parameter and Meteorological Conditions

“…The negative relationships linking wind velocity to ozone concentration (Fig. 5) could be explained by a dilution effect with wind activity which leads to a lowering of ozone levels (Lorenzini et al 1995;Ellis et al 2000) and, consequently, lower plant leaf injury. Increasing wind speed of north winds coming from the Mediterranean basin tends to reduce the resistance of the land surface to the deposition of ozone and may result in a decrease of ozone concentration levels.…”

“…Winddriven circulation of this air pollutant in the atmosphere can make its concentrations higher than the usually measured levels in remote areas located hundreds of kilometers from the original pollutant source. In addition to wind advection, ozone pollution is further promoted by higher temperatures, greater solar radiation, and lower relative humidity (Ellis et al 2000). Likewise, the pollutant's harmful effects are generally more acute during summer (Ribas and Peñuelas 2006), although maximal ozone concentration values were also reported to occur during winter as well (Naja et al 2003;Khemani et al 1995;Ribas and Peñuelas 2006) due to considerably greater lifetimes for both ozone and its precursors under cold weather conditions (Liu et al 1987).…”