Nick Molden | Imperial College London (original) (raw)

Papers by Nick Molden

Atmospheric Environment, 2016

Occupational and environmental health

SAE Technical Paper Series

Several governments are increasing the blending mandate of renewable fuels to reduce the life-cyc... more Several governments are increasing the blending mandate of renewable fuels to reduce the life-cycle greenhouse gas emissions of the road transport sector. Currently, ethanol is a prominent renewable fuel and is used in low-level blends, such as E10 (10 %v/v ethanol, 90 %v/v gasoline) in many parts of the world. However, the exact concentration of ethanol amongst other renewable fuel components in commercially available fuels can vary and is not known.To understand the impact of the renewable fuel content on the emissions from Euro 6d-TEMP emissions specification vehicles, this paper examines the real-driving emissions (RDE) from four 2020 to 2022 model-year vehicles run on E0 and E10 fuels. CO, CO2, NO, and NO2 were measured through a Portable Emissions Measuring System (PEMS). In addition, N2O, formaldehyde, acetaldehyde, volatile organic compounds (VOCs), and other gaseous and particulate tailpipe emissions were measured and categorized in cold-start, urban, rural, and motorway se...

Environment International

Annals of Work Exposures and Health

Tyre wear particles (TWPs) are a predominant component of particulate air pollution from road tra... more Tyre wear particles (TWPs) are a predominant component of particulate air pollution from road transport and emissions may increase in future due to increasing use of heavier cars. We hypothesized that inhaled respirable TWPs would have adverse effects on human lung alveolar epithelium, which would differ between alveolar type 1 (AT1; gas exchanging) and type 2 (AT2; secretory) cells. Two real-time road-generated samples were each collected into Milli-Q water using custom-made apparatus whilst driving a car for 2h: S1) high, behind the tyre (“pure” TWP) and S2) low, sideways to the tyre (mixed TWP/brake/road wear). Alveolar epithelial type 1-like (AT1L) and type 2-like (AT2L) cell lines were exposed for 24h to each TWP sample at 62.5-250µg/ml. The response differed between AT1L and AT2L cells. AT1L cell viability/metabolism and cytotoxity (MTT/LDH assays) were unaffected by either TWP sample, whereas AT2L cell metabolic activity increased (MTT measures metabolic activity) at all conc...

The purpose of this study was to identify a characteristic elemental tyre fingerprint that can be... more The purpose of this study was to identify a characteristic elemental tyre fingerprint that can be utilised in atmospheric source apportionment calculations. Currently zinc is widely used as a single element tracer to quantify tyre wear, however several authors have highlighted issues with this approach. To overcome this, tyre rubber tread was digested and has been analysed for 25 elements by ICP-MS to generate a multielement profile. Additionally, to estimate the percentage of the tyre made up of inert fillers, thermogravimetric analysis was performed on a subset. Comparisons were made between passenger car and heavy goods vehicle tyre composition, and a subset of tyres had both tread and sidewall sampled for further comparison. Finds showed 19 of the 25 elements were detected in the analysis. The mean mass fraction of zinc detected was 11.17 g/kg, consistent with previous estimates of 1% of the tyre mass. Aluminium, iron, and magnesium were found to be the next most abundant elemen...

Sustainability

Travellers may be exposed to a wide range of different air pollutants during their journeys. In t... more Travellers may be exposed to a wide range of different air pollutants during their journeys. In this study, personal exposures within vehicles and during active travel were tested in real-world conditions across nine different transport modes on journeys from London Paddington to Oxford City Centre, in the United Kingdom. The modes tested covered cycling, walking, buses, coaches, trains and private cars. Such exposures are relevant to questions of traveller comfort and safety in the context of airborne diseases such as COVID-19 and a growing awareness of the health, safety and productivity effects of interior air quality. Pollutants measured were particle number (PN), particle mass (PM), carbon dioxide (CO2) and speciated volatile organic compounds (VOCs), using devices carried on or with the traveller, with pumped sampling. Whilst only a relatively small number of journeys were assessed—inviting future work to assess their statistical significance—the current study highlights where...

Johnson Matthey Technology Review

The hypothesised Euro 7 exhaust emissions regulation will be important both from the perspective ... more The hypothesised Euro 7 exhaust emissions regulation will be important both from the perspective of how it further improves air quality, but also of certain greenhouse gas emissions and the economics of the internal combustion engine. This paper sets out the on-going importance of ozone to urban air quality, and how tailpipe volatile organic compound (VOC) emissions contributes to that as well as having direct human health effects through inhalation. The paper then sets out a novel method for the measurement of speciated VOCs and nitrous oxide (N2O) at the tailpipe in real-world conditions, and presents initial results across a range of modern light-duty vehicles. Based on the results, may be the case that VOCs should be a higher priority for future regulation than N2O, although more research is required to achieve a consensus on typical real-world N2O emissions.

SAE International Journal of Commercial Vehicles

SAE International Journal of Commercial Vehicles, Apr 5, 2022

SAE International Journal of Commercial Vehicles, 2019

Vehicle cabin air quality depends on various parameters such as number of passengers, fan speed, ... more Vehicle cabin air quality depends on various parameters such as number of passengers, fan speed, and vehicle speed. In addition to controlling the temperature inside the vehicle, HVAC control system has evolved to improve cabin air quality as well. However, there is no standard test method to ensure reliable and repeatable comparison among different cars. The current study defined Cabin Air Quality Index (CAQI) and proposed a test method to determine CAQI. CAQI particles showed dependence on the choice of metrics among particle number (PN), particle surface area (PS), and particle mass (PM). CAQI particles is less than 1 while CAQI CO2 is larger than 1. The proposed test method is promising but needs further improvement for smaller coefficient of variations (COVs).

Science of The Total Environment, 2021

There has been ongoing research aimed at reducing pollution concentrations in vehicles due to the... more There has been ongoing research aimed at reducing pollution concentrations in vehicles due to the high exposure which occurs in this setting. These studies have found using recirculate (RC) settings substantially reduces in-cabin traffic-related pollution concentrations but possibly leads to an adverse accumulation of carbon dioxide (CO2) from driver respiration. The aim of this study was to highlight how vehicle models and ventilation settings affect in-cabin concentrations to ultrafine particles (UFP) and CO2 in real-world conditions. We assessed the ability of different vehicles to balance reductions in UFP against the build-up of in-cabin CO2 concentrations by measuring these pollutants concurrently both inside and outside the vehicle to derive an in/out ratio. When ventilation settings were set to RC, UFP concentrations inside the vehicles (median: 3205 pt./cm3) were 86% lower compared to outside air (OA) (23,496 pt./cm3) across a 30-min real-world driving route. However, CO2 concentrations demonstrated a rapid linear increase under RC settings, at times exceeding 2500 ppm. These concentrations have previously been associated with decreased cognitive performance. Our study did not find an effect of gasoline fuelled vehicles affecting in-cabin UFP levels compared to hybrid or electric vehicles, suggesting that self-pollution was not an issue. We also found that certain vehicle models were better at reducing both in-cabin UFP and CO2 concentrations. The results suggest that under RC settings in/out CO2 ratios are largely determined by the leakiness of the vehicle cabin, whereas in/out UFP ratios are primarily determined by the efficacy of the in-built air filter in the vehicles ventilation system.

Atmospheric Environment, 2020

This paper reviews the emissions performance of 39 Euro 6 diesel passenger cars using a Portable ... more This paper reviews the emissions performance of 39 Euro 6 diesel passenger cars using a Portable Emissions Measurement System (PEMS). Comparisons are made with current emissions regulations (in particular the Euro 6 standard for nitrogen oxides (NOx = NO+ NO2) of 0.80 g km -1 ) and predictions by the speed dependent emission factors of COPERT. The mean NOx emission was 0.36 ± 0.36 g km -1 , the mean nitrogen dioxide (NO2) emission was 0.17 ± 0.19 g km -1 . The average fraction NOx emitted as NO2 (known as primary NO2 or fNO2) was 44%. Each vehicle was analysed over a test route composed of urban and motorway driving. On average NOx emissions were 5.3 times the Euro 6 limit for urban driving and 3.8 times the limit for motorway. A wide range of deviation ratios (ratio between real world measurements and type approval limit) were found, the highest being 27.3 for an urban section. The average PEMS measured NOx emission was 1.6 times COPERT’s average estimate. Similarly with primary NO...

The average person now spends more than 90% of their time indoors, with around one hour of this s... more The average person now spends more than 90% of their time indoors, with around one hour of this spent inside vehicles. This is referred to as Vehicle Interior Air Quality (VIAQ). This exposure is important to understand given the immediate proximity to significant pollutant sources (other vehicles), plus in urban areas, high outdoor concentrations. However, there are also significant sources of pollution from inside the vehicle. Volatile Organic Compounds (VOCs), responsible for the “new car smell”, can be emitted from an array of interior parts and components: the dashboard, interior panels, flooring materials, and many others. Within the confined space of a vehicle, VOCs emitted from these components may reach levels that are potentially harmful to human occupants, causing symptoms such as nausea, allergies, fatigue, stinging eyes, and headaches. Beyond affecting drivers’ and passengers’ well-being and comfort, such symptoms may have also consequences on safe driving. NAQTS and Em...

Many studies have addressed outdoor air pollution that arises from traffic, and its associated ne... more Many studies have addressed outdoor air pollution that arises from traffic, and its associated negative impacts on public health. However, less is being done to understand indoor air pollution, despite the average person now spending more than 90% of their time indoors (European Commission, 2004). In-cabin air quality represents around one hour of this exposure (Muller et al. 2011), but is especially important given the immediate proximity to motor vehicles, plus, in urban areas, high ambient concentrations compared to other micro-environments. To address the dearth of research on this topic, an NAQTS V1000 air quality monitor, conveniently housed in a mannequin (“Justin”), was used to monitor inside vehicles: five pollutants were monitored (PN, CO, CO2, NO2, VOCs) along with environmental and road comfort parameters. Consistent with other research (CARB, 2015; Muller et al. 2011), our data shows that the measured pollutants are often several times higher than those outside, due to ...

h i g h l i g h t s OBD ubiquitous in modern vehicles, PEMS to be regulatory requirement in Europ... more h i g h l i g h t s OBD ubiquitous in modern vehicles, PEMS to be regulatory requirement in Europe. Maps of transient fuel use, emissions recreated from real-world driving data. Trip-level fuel use and emissions within 5% of observed values generally. Per second fuel use and emissions simulated accurately.