Search Results (4)

Understanding the temporal dynamics of urban air pollution is essential for effective environmental management, yet the nonlinear and scale-dependent behavior of key pollutants remains insufficiently explored. This study examines the multifractal properties of fine particulate matter ($P{M}_{2.5}$), ozone ($O_3$), and the Air Quality Index (AQI) across four major urban locations in California—Los Angeles, Orange, Riverside–Rubidoux, and Riverside–Mira Loma—regions characterized by persistent air-quality challenges and high population exposure. Using Multifractal Detrended Fluctuation Analysis (MF-DFA), we assess long-range dependence, heterogeneity, and cross-pollutant interactions to address the central question of whether these pollutants exhibit genuine multifractal behavior and how it varies across locations. The results reveal strong multifractality in all series, with spectrum widths ranging from 0.42 to 0.71 for $P{M}_{2.5}$-AQI and from 0.28 to 0.46 for $O_3$-AQI, indicating pronounced scale-dependent variability. Los Angeles consistently exhibited the widest spectra, reflecting greater temporal complexity. The generalized Hurst exponent at $q=2$ remained between 0.52 and 0.58 across all pollutant pairs, indicating persistent dynamics. Surrogate-data testing further confirmed that 60–75% of the observed multifractality arises from intrinsic long-range correlations rather than distributional effects. Overall, this study demonstrates that urban air pollutants in California display rich multifractal structures that differ systematically across regions, reflecting local emission patterns and atmospheric processes. These findings highlight the relevance of multifractal analysis as a powerful tool for improving air-quality modeling, forecasting, and policy design in densely populated environments. Full article

In the winter season, citrus nursery production faces challenges including shorter days, lower light levels, and lower temperatures that delay vegetative budbreak and scion shoot growth. With the goal of improving the production cycle in the citrus nursery, we investigated the effect of supplemental LED light on the production of bud-grafted citrus trees during short winter days. Three experiments were conducted under different temperature conditions. “Washington” Navel sweet orange (Citrus sinensis) was budded on Carrizo citrange (C. sinensis × Poncirus trifoliata) and Rubidoux trifoliate (P. trifoliata) rootstocks in early December. Light treatments included no supplemental light, day-length extension to 16 h with LED light, and night interruption (1 h of LED light at night). Day-length extension and night interruption were studied with and without preconditioning plants with the respective light treatments for 6 weeks before grafting. Day-length extension increased the scion growth, but only when supplemental heating was provided, implying that low temperatures are a limiting factor for plant growth. Growth effects were stronger when the Navel scion was grafted on Carrizo compared to Rubidoux, likely because of the higher dormancy of the latter rootstock. Night interruption did not affect scion budbreak or growth under any of the tested conditions. Preconditioning enhanced scion growth in some instances. The results suggest that the use of supplemental LED light to extend the day length may increase plant growth during the short winter days, but the effects are limited under low-temperature conditions. Full article

Background: Huanglongbing (HLB) is currently one of the most devasting diseases in citrus plants worldwide. Resistance against its causal agent, Candidatus Liberibacter asiaticus (CLas), in commercial Citrus species remains a challenge, even though they show differences in CLas multiplication. Methods: A total of 14 citrandarins and their parents (Sunki mandarin and Poncirus trifoliata cv. Rubidoux) were top-grafted onto the canopy of potted ‘Valencia’ sweet orange plants with high CLas titers. The grafted genotypes were tested for CLas infection and physiological effects of the disease (starch accumulation and callose deposition) for 12 months. Results: All tested genotypes were infected by CLas during the time frame of the experiment. However, a decrease in the infection rate ranging from 50% to 80% for the hybrids H109, H126, H157, and H222 was observed 360 days from the top-grafting. CLas was undetected by real-time PCR in H106 at the end of the experiment, which had low levels of starch and callose deposition. Conclusions: CLas infected all of the tested citrandarins, but a decrease in the infection rate over time was detected for some specific genotypes, which led to less starch accumulation and callose deposition. Full article

To evaluate the feasibility of the Sunset semicontinuous organic and elemental carbon (OC/EC) monitor, the U.S. Environmental Protection Agency (EPA) sponsored the deployment of this monitor at Chemical Speciation Network (CSN) sites with OC and EC measurements via quartz fiber filter collection in Chicago, Illinois; Houston, Texas; Las Vegas, Nevada; St. Louis, Missouri; Rubidoux, California; and Washington, D.C. Houston, St. Louis, and Washington also had collocated Aethalometer black carbon (BC) measurements. Sunset OC generally compared well with the CSN OC (r² = 0.73 across five sites); the Sunset/CSN OC ratio was, on average, 1.06, with a range among sites of 0.96 to 1.12. Sunset thermal EC and CSN EC did not compare as well, with an overall r² of 0.22, in part because 26% of the hourly Sunset EC measurements were below the detection limit. Sunset optical EC had a much better correlation to CSN EC (r² = 0.67 across all sites), with an average Sunset/CSN ratio of 0.90 (range of 0.7 to 1.08). There was also a high correlation of Sunset optical EC with Aethalometer BC (r² = 0.77 across all sites), though with a larger bias (average Sunset/Aethalometer ratio of 0.56). When the Sunset instrument was working well, OC and OptEC data were comparable to CSN OC and EC. Full article