A dual-method approach toward measuring the built environment - sampling optimization, validity, and efficiency of using GIS and virtual auditing.

In recent years, GIS and virtual auditing have been widely used to measure the built environment, and each method carries its strengths and weaknesses. To generate higher quality, more cost-effective, and less time-consuming measures, it is necessary to explore dual- or multi-method strategy toward sampling optimization, improvement of measurement, and enhancement of efficiency. To justify the proposed dual-method approach, the study has three major objectives. First, it examines the uncertainties associated with different sample sizes by using GIS to generate scenarios that contrast the validity of measurements to aid sampling optimization in auditing. Second, it compares the validity of GIS measures with those generated through Google Street View Auditing (GSVA) by human raters. Third, it further examines the efficiency of the proposed dual-method approach in comparison to the two individual methods. Such investigation generates several novel findings. First, the study presents important evidence to support that GIS measures can offer sampling guidance applicable to the GSVA method. It leads to a recommendation of sampling sizes (5%-20%) for cases in settings with a mixture of affluent and disadvantaged neighborhoods. Results further indicate that different communities and certain individual features and characteristics may demand different sampling practices. Second, the study found that while GSVA is trustworthy for most characteristic variables, especially those that required subjective input, GIS provides well-validated measures for certain objective environmental attributes. Furthermore, the study reports that a dual-method approach of GIS and GSVA had a lower financial and time burden than using GSVA alone and is thus recommended as a comprehensive solution for optimal measurement of an objective built environment in mixed urban neighborhoods.

Correction to: Neighborhood Parks and Recreationists' Exposure to Ozone: A Comparison of Disadvantaged and Affluent Communities in Los Angeles, California.

The original version of the article contained an error in the Exposure to Ozone section, paragraph 4, the 1st sentence, reporting the finding that male recreationists experienced higher ozone dose exposure than female recreationists, the number should be males M = 77.08.

Neighborhood Parks and Recreationists' Exposure to Ozone: A Comparison of Disadvantaged and Affluent Communities in Los Angeles, California.

Urban parks are valued for their benefits to ecological and human systems, likely to increase in importance as climate change effects continue to unfold. However, the ability of parks to provide those myriad benefits hinges on equitable provision of and access to green spaces and their environmental quality. A social-ecological approach was adopted in a study of urban park use by recreationists in the City of Los Angeles, contrasting two affluent and two disadvantaged communities situated in coastal and inland zones. Twenty-four days of observations distributed across morning and afternoon time blocks were gathered, with observations in each day drawn from a pair of affluent and disadvantaged community parks. Observers noted location, gender, age, ethnicity/race, and level of physical activity of each visitor encountered during four scheduled observation sweeps on each day of field work. In addition, ozone dose exposure was measured through passive monitoring. Ozone dose exposure was calculated using average hourly ozone in ppb multiplied by METS (metabolic expenditures). Dose exposure was significantly higher in the disadvantaged community parks (with majority Latino use). Findings suggest that additional monitoring in disadvantaged communities, especially inland, may be prudent to facilitate community-based information as well as to assess the degree of potential impact over time. Additionally, mitigative strategies placed in urban parks, such as increased tree canopy may help to reduce the degree of risk and improve community resilience. Future research examining the positive outcomes from physically active use of urban parks may benefit from adopting a nuanced approach in light of the present findings.

Contrasting physiological responses of ozone-tolerant Phaseolus vulgaris and Nicotiana tobaccum varieties to ozone and nitric acid.

Ozone (O3) and nitric acid (HNO3) are synthesized by the same atmospheric photochemical processes and are almost always co-pollutants. Effects of O3 on plants have been well-elucidated, yet less is known about the effects of HNO3 on plants. We investigated the physiological effects of experimental O3 and HNO3 fumigation on Phaseolus vulgaris (snap bean) and Nicotiana tobaccum (tobacco) varieties with known sensitivity to O3, but unknown responses to HNO3. Responses were measured as leaf absorptance, aboveground plant biomass, and photosynthetic CO2-response curve parameters. Our results demonstrate that O3 reduced absorptance, stomatal conductance and plant biomass in both species, and maximum photosynthetic rate in P. vulgaris, whereas the main effect of HNO3 was an increase in mesophyll conductance. Overall, the results suggest that HNO3 affects mesophyll conductance through increased nitrogen absorbed by leaves during HNO3 deposition which in turn increases photosynthetic demand for CO2, or that damage to epicuticular waxes on leaves increased diffusion of CO2 to sites of carboxylation.

Eutrophic lichens respond to multiple forms of N: implications for critical levels and critical loads research.

Epiphytic lichen communities are highly sensitive to excess nitrogen (N), which causes the replacement of native floras by N-tolerant, "weedy" eutrophic species. This shift is commonly used as the indicator of ecosystem "harm" in studies developing empirical critical levels (CLE) for ammonia (NH3) and critical loads (CLO) for N. To be most effective, empirical CLE and/or CLO must firmly link lichen response to causal pollutant(s), which is difficult to accomplish in field studies in part because the high cost of N measurements limits their use. For this case study we synthesized an unprecedented array of atmospheric N measurements across 22 long-term monitoring sites in the Los Angeles Basin, California, USA: gas concentrations of NH3, nitric acid (HNO3), nitrogen dioxide, and ozone (n = 10 sites); N deposition in throughfall (n = 8 sites); modeled estimates of eight different forms of N (n = 22 sites); and nitrate deposition accumulated on oak twigs (n = 22 sites). We sampled lichens on black oak (Quercus kelloggii Newb.), and scored plots using two indices of eutroph (N tolerant species) abundance to characterize the community-level response to N. Our results contradict two common assertions about the lichen-N response: (1) that eutrophs respond specifically to NH3 and (2) that the response necessarily depends upon the increased pH of lichen substrates. Eutroph abundance related significantly but weakly to NH3 (r2 = 0.48). Total N deposition as measured in canopy throughfall was by far the best predictor of eutroph abundance (r2 = 0.94), indicating that eutrophs respond to multiple forms of N. Most N variables had significant correlations to eutroph abundance (r2 = 0.36-0.62) as well as to each other (r2 = 0.61-0.98), demonstrating the risk of mistaken causality in CLE/CLO field studies that lack sufficient calibration data. Our data furthermore suggest that eutroph abundance is primarily driven by N inputs, not substrate pH, at least at the high-pH values found in the basin (4.8-6.1). Eutroph abundance correlated negatively with trunk bark pH (r2 = 0.43), exactly the opposite of virtually all previous studies of eutroph behavior. This correlation probably results because HNO3 dominates N deposition in our study region.

Image analysis of epicuticular damage to foliage caused by dry deposition of the air pollutant nitric acid.

Nitric acid vapor is produced by the same photochemical processes that produce ozone. In the laboratory, concentrated nitric acid is a strong acid and a powerful oxidant. In the environment, where the concentrations are much lower, it is an innocuous source of plant nitrogen. As an air pollutant, which mode of action does dry deposition of nitric acid follow? We investigated the effects of dry deposition of nitric acid on the foliage of four tree species native to the western United States. A novel controlled environment, fumigation system enabled a four-week exposure at concentrations consistent with ambient diurnal patterns. Scanning electron microscopy and automated image analysis revealed changes in the epicuticular wax layer during fumigation. Exposure to nitric acid resulted in a reproducible suite of damage symptoms that increased with increasing dose. Each tree species tested exhibited a unique set of damage features, including cracks, lesions, and conformation changes to epicuticular crystallite structures. Dry deposition of atmospheric nitric acid caused substantial perturbation to the epicuticular surface of all four tree species investigated, consistent with the chemical oxidation of epicuticular waxes. Automated image analysis eliminated many biases that can trouble microscopy studies. Trade names and commercial enterprises or products are mentioned solely for information. No endorsements by the U.S. Department of Agriculture are implied.

Foliar loading and metabolic assimilation of dry deposited nitric acid air pollutants by trees.

Dry deposition of nitric acid vapor (HNO(3)) is a major contributor to eutrophication of natural ecosystems. Although soil fertilization by nitrogen deposition is considered to be the primary pathway for changes in plant nutrient status and shifts in ecological structure, the aerial portion of plants offer many times the surface area in which to collect atmospheric HNO(3). As much as 60% of deposited nitrogen may be retained in the canopy and not land on the soil surface below. Although uptake and assimilation appears to contribute to retention, only a small percentage of dry deposition is recovered in assimilated N pools. To test the importance of biological activity on the process and measurements of dry deposition, we used controlled environmental chambers to compare deposition to living and freeze-dried foliage of four tree species using (15)N-labeled HNO(3). In living trees, assimilation was determined by (15)N incorporation into free amino acids and proteins in leaves and roots. From 10% to 60% of the retained HNO(3) was incorporated into the biologically active nitrogen pool. The remainder was bound to foliar surfaces in an insoluble form in either living or freeze-dried foliage. The importance of the boundary layer conditions emerged as a primary factor controlling dry deposition characteristics and measurements.Trade names and commercial enterprises or products are mentioned solely for information. No endorsements by the U.S. Department of Agriculture are implied.

Monitoring fugitive dust emissions from off-highway vehicles traveling on unpaved roads and trails using passive samplers.

Vehicles traveling on dry, unpaved roads generate copious quantities fugitive dust that contributes to soil erosion, and potentially threatens human health and ecosystems. The purpose of this study was to develop a low-cost technique for monitoring road dust that would enable land managers to estimate soil loss. The "sticky-trap" collectors developed were evaluated at the Turkey Bay off-highway vehicle (OHV) riding area on the Land Between the Lakes National Recreation Area, in western Kentucky. The results showed that the dust plume created by vehicle traffic was heterogeneous: larger particles were in the lower part of the plume and deposited closer to the source, smaller particles were carried higher in the plume and traveled at least 100 m away from the source. Collection of particles parallel to the source was also heterogeneous, suggesting that measurements taken at a single point may not be appropriate for estimating erosion losses. Measurements taken along two trails indicate that when large numbers of riders are present, dust concentrations may reach unhealthful conditions for riders, but that it is unlikely that fugitive dust is harming native vegetation, given frequent rainfall. The study demonstrated that OHV traffic contributes to substantial erosion of roadbeds because of aeolian transport.

Vertical distribution of ozone and nitric acid vapor on the Mammoth Mountain, eastern Sierra Nevada, California.

In August and September 1999 and 2000, concentrations of ozone (O3) and nitric acid vapor (HNO3) were monitored at an elevation gradient (2184-3325 m) on the Mammoth Mountain, eastern Sierra Nevada, California. Passive samplers were used for monitoring exposure to tropospheric O3 and HNO3 vapor. The 2-week average O3 concentrations ranged between 45 and 72 ppb, while HNO3 concentrations ranged between 0.06 and 0.52 microg/m3. Similar ranges of O3 and HNO3 were determined for 2 years of the study. No clear effects of elevation on concentrations of the two pollutants were detected. Concentrations of HNO3 were low and at the background levels expected for the eastern Sierra Nevada, while the measured concentrations of O3 were elevated. High concentrations of ozone in the study area were confirmed with an active UV absorption O3 monitor placed at the Mammoth Mountain Peak (September 5-14, 2000, average 24-h concentration of 56 ppb).