Effects of climate change on the wash-off of volatile organic compounds from urban roads

Characteristics of dissolved organic matter in two alternative water sources: A comparative study between reclaimed water and stormwater

Reclaimed water and stormwater are two important alternative water sources to mitigate water resource shortage. They can be reused by discharging into drinking water sources. Due to different sources, characteristics of dissolved organic matter (DOM, a precursor of disinfection by-products, DBPs) present in reclaimed water and stormwater would be different. This study selected reclaimed water to compare with stormwater (including both stormwater runoff and rainwater) by investigating their DOM characteristics, including concentrations, aromaticity, molecular weight, hydrophobicity/hydrophilicity, composition and DBPs formation potential. The results showed that reclaimed water had higher dissolved organic carbon (DOC) concentrations (6.02-10.8 mg/L) than stormwater (3.62-5.48 mg/L) while SUVA₂₅₄ values of stormwater runoff (1.92-2.53 L/(mg-C·m)) were higher than reclaimed water (1.11-1.24 L/(mg-C·m)). Additionally, reclaimed water is more hydrophobic while stormwater runoff and rainwater are more hydrophilic. Although all water types included the highest fraction of DOM with molecular weight <1 kDa (43.0 %-77.5 %), reclaimed water primarily contained soluble microbial products (SMPs)-like and humic acid-like substances while stormwater runoff primarily contained humic acid-like DOM. In terms of DBPs, reclaimed water showed relatively higher formation potential than stormwater runoff while rainwater had the lowest DBPs formation potential. These results can contribute to effective water resource management. Particularly, when reclaimed water or/and stormwater are discharged into drinking water sources, these outcomes can help on efficient drinking water treatment.

Understanding nutrient dynamics for effective stormwater treatment design

Current stormwater quality modelling tools lack robust mathematical replication of nutrient entrainment in runoff. This makes it challenging to design effective stormwater treatment systems such as nature based solutions with adequate resilience to future changes in nutrient inputs in urban environments. Consequently, poorly treated stormwater can be discharged into receiving waters, leading to nutrient enrichment and in turn, environmental and human health impacts. This study integrated empirically based with statistical modelling techniques to incorporate nutrient dynamics into commonly used Intensity-Frequency-Duration (IFD) distributions of design rainfall. Field based nutrient wash-off experiments were conducted to understand nutrient behaviour during a runoff event. New mathematical formulations were derived to describe the decay (wash-off) of nutrients. Rainfall intensity, duration and initially accumulated pollutant load exert positive influence on the decay of nitrogen and phosphorous, while organic carbon has a negative impact on phosphorus decay. It was also evident that nitrogen species would decay at a similar rate, while phosphorus species may decay at different rates. Compared to nitrogen species, phosphorous species were found more likely to be washed-off during a rainfall event. Using the mathematical formulations developed, wash-off of nitrogen and phosphorous was simulated for 435 very frequent and frequent/infrequent design rainfall events leading to the creation of Intensity-Frequency-Duration-Wash-off (IFDW) curves. Analysis of uncertainty associated with IFDW indicated that total phosphorous could be completely washed-off during most of the design rainfall events, while total nitrogen would only be completely washed-off by very few events that are rarer than 10 % AEP (annual exceedance probability). IFDW can act as a tool for supporting effective stormwater treatment design in order to promote sustainable stormwater management and reuse.

Measurements, emission characteristics, and control methods of fire effluents generated from tunnel asphalt pavement during fire: a review

Tunnels are widely used in high-grade roads, particularly in mountainous areas; however, tunnel fires often result in severe economic losses and casualties. The fire effluents produced from asphalt pavement have attracted significant research attention. The main objective of this study is to assimilate information on various aspects of bituminous mixture emissions during fires. In this study, the fume emissions of bitumen and bituminous mixtures during combustion are comprehensively reviewed and summarized. First, the test methods for fire effluents produced by bitumen and bituminous mixtures after combustion are summarized. Second, the factors influencing the fume concentration and composition are determined. In addition, different methods to reduce the emission of fire effluents are compared, particularly for the suppression of toxic gas emissions. Then, reasonable suggestions are proposed to reduce the damage caused by hazardous gases to humans and the environment. This review is beneficial for comprehensively understanding the fume emission behaviour and future research on the smoke suppression of highway tunnel asphalt pavements during fires.

The effects of land use characteristics on urban stormwater quality and watershed pollutant loads

Urban developments can result in higher runoff and nutrient loadings transported to downstream receiving waterbodies. While much effort has been made recently in watershed restoration in the U.S., a lack of recent runoff quality data limits the prediction capability of urban watershed models. The objectives of this study was to fill an existing information gap on how rainfall and land uses interact and affect such loadings. This study instrumented six coastal urban catchments, each dominated by a single land use. We measured total nitrogen (TN), total phosphorus (TP), total suspended solids (TSS), total Kjeldahl Nitrogen (TKN), ortho-P, and nitrate concentrations in runoff from 30 storm events over one year from six urban land uses, namely commercial, industrial, transportation, open space, low density residential, and high density residential. Results indicated that the median event mean concentrations (EMCs) for TSS, TP, and TN were 30 (19-34), 0.31 (0.26-0.31), and 0.94 (0.73-1.25) mg L^-1, respectively. TSS EMCs from the open space and industrial land uses were significantly greater than other land uses; there were positive correlations between TN concentrations and imperviousness and between TP concentrations and turf coverage. Both the amount and intensity of rainfall positively influenced TSS concentrations in runoff regardless of land use. Using the collected data, this study developed a generic equation for predicting the loading of a pollutant as a function of rainfall depth. This equation was verified by comparing its predictions with the simulations of a sufficiently-calibrated water quality model in terms of TSS, TP, and TN loadings from various land uses in another coastal catchment for a period of ten years. Average TSS, TN, and TP loadings from the catchment were estimated to be 0.86, 0.03, and 0.01 kg ha^-1 cm^-1, respectively.

Characterizing petroleum hydrocarbons deposited on road surfaces in urban environments

Petroleum hydrocarbons are a toxic pollutant group, primarily including volatile organic compounds (VOC), semi-volatile organic compounds (SVOC) and non-volatile organic compounds (NVOC). These pollutants can be accumulated on urban roads during dry periods and then washed-off by stormwater runoff in rainy days. Unlike heavy metals and polycyclic aromatic hydrocarbons, petroleum hydrocarbons have not received an equal attention in the field of stormwater pollutant processes. This paper investigated characteristics of VOC, SVOC and NVOC pollutant loads deposited on urban roads and their influential factors using a forward stepwise regression and PROMETHEE-GAIA analysis techniques. The results indicate that the loads deposited on urban roads were NVOC > SVOC > VOC. It is also noted that the degrees of factors in influencing petroleum hydrocarbons deposited on urban roads did not equal and their order was total solids > land use type > vehicular traffic > roughness of road surfaces. The research results also showed that petroleum hydrocarbons on urban road surfaces tend to be source limiting rather than transport limiting. These outcomes can contribute to petroleum hydrocarbons polluted stormwater management, such as treatment system design and stormwater modelling approach improvement.

Modelling benzene series pollutants (BTEX) build-up loads on urban roads and their human health risks: Implications for stormwater reuse safety

Benzene series compounds (BTEX) are toxic pollutants primarily generated by traffic activities in an urban environment. BTEX pollutants can be deposited (build-up) on urban road surfaces during dry periods and then washed-off into stormwater runoff. Since BTEX pollutants can pose high human health risks, they can undermine stormwater reuse safety after they enter stormwater runoff. In this study, the BTEX pollutants build-up loads on urban road surfaces were investigated in Shenzhen, China. An artificial neural network (ANN) approach and two conventional regression modelling approaches were compared in terms of estimating BTEX build-up loads based on land use related parameters. It was found that the ANN approach had a better performance than the two regression modelling approaches. Additionally, the spatial distribution maps and human health risk map of BTEX pollutants build-up created using the ANN approach can provide a robust visualization platform to identify 'hot-spot' areas. These areas have a potential to generate highly BTEX polluted stormwater runoff and hence be inappropriate to be reused. These research outcomes are expected to provide an effective approach for ensuring stormwater reuse safety and a useful guidance for decision-making for stormwater management and water environment protection related urban planning.

Role of Sediments in Insecticide Runoff from Urban Surfaces: Analysis and Modeling

Insecticides, such as pyrethroids, have frequently been detected in runoff from urban areas, and their offsite transport can cause aquatic toxicity in urban streams and estuaries. To better understand the wash-off process of pesticide residues in urban runoff, the association of pyrethroids with sediment in runoff from residential surfaces was investigated in two watersheds located in Northern California (Sacramento County). Rainfall, flow rate, and event mean concentrations/loads of sediments and pyrethroids, collected during seasonal monitoring campaigns from 2007 to 2014, were analyzed to identify relationships among stormwater quality and rainfall characteristics, primarily using Principal Component Analysis (PCA). Pyrethroid wash-off was strongly related to sediment wash-off whenever sediment loads exceeded 10 mg; this value was conveniently selected as a threshold between dissolved and particle-bound control of off-site pyrethroid transport. A new mechanistic model for predicting pyrethroid wash-off profiles from residential surfaces at basin-scale was implemented in the Storm Water Management Model (SWMM). The accuracy of the model predictions was estimated by evaluating the root mean square error (RMSE), Nash–Sutcliff efficiency (NSE), and Kling–Gupta efficiency (KGE) for each pyrethroid detected (RMSE_tot = 0.13; NSE_tot = 0.28; KGE_tot = 0.56). The importance of particle-bound transport revealed in this work confirms previous field investigations at a smaller scale, and it should be a key consideration when developing policies to mitigate pesticide runoff from urban areas.

Multi-year evaluation of ambient volatile organic compounds: temporal variation, ozone formation, meteorological parameters, and sources

The multi-year characteristics of ambient volatile organic compounds (VOCs) and their source contribution in a selected metropolitan (Seoul) and rural (Seokmolee) areas in Korea were investigated to provide the framework for development and implementation of ambient VOC control strategies. For Seoul, none of the three VOC groups exhibited any significant trend in their ambient concentrations, whereas for Seokmolee, they all showed a generally decreasing trend between 2005 and 2008 and an increasing trend after 2008. Two paraffinic (ethane and propane) and two olefin (ethylene and propylene) hydrocarbons displayed higher concentrations during the cold season than warm season, while the other target VOCs did not exhibit any significant trends. Ethylene and toluene were the first and second largest contributors to ozone formation, respectively, whereas several other VOCs displayed photochemical ozone formation potential values less than 0.01 ppb. For both areas, there was a significant negative correlation between ambient temperature and the selected VOC group concentrations. In contrast, a significant positive correlation was observed between relative humidity and the three VOC group concentrations, while no significant correlation was observed between wind speed and VOC group concentrations. For Seoul, the combination of vehicle exhaust and gasoline/solvent evaporation was the greatest source of VOCs, followed by liquid natural gas (LNG) and liquid petroleum gas (LPG). However, combination of LNG and LPG was the greatest source of VOCs at Seokmolee, followed by the combination of vehicle exhaust and gasoline evaporation, and then biogenic sources.

Sources of organic matter in first flush runoff from urban roadways

This study aims to explore the influential sources of organic matter in first flush runoff from urban roadways by comparing organic carbon content and particle size distribution in road dust with those from discharge from vehicles during rainfall. Samples on first flush runoff and road dust were collected from urban roadways. In addition, vehicle drainage was assumed to flow from vehicles during rainfall events, so vehicle wash-off water was collected by spraying water onto the top and from the underside of vehicles to simulate accumulation during a vehicle run. In road dust, the organic carbon content in the <0.2 mm fraction was about twice that of the 0.2-2 mm fraction. The particle size distributions of both first flush runoff and vehicle wash-off water were similar, and particles <0.2 mm contributed to over 95% of the total volume. The dissolved organic carbon concentration in the vehicle wash-off water was considerably higher than that in the road dust/water mixture. The total organic carbon content in road dust was positively correlated with annual daily traffic. Therefore, vehicles were thought to strongly influence the nature of road dust.