Infants in prams breathe more polluted air than adults pushing them, as their breathing zone lies closer to traffic emissions and road-level pollutants. The fine particle levels are up to 44 percent higher at pram height, and as much as 72 percent higher particle number concentrations in the lower seats of double prams. These findings highlight the need for cleaner urban design, Smarter air filtration, and sustainable energy systems to create healthier, net-zero cities that truly breathe.

On a warm, late-summer morning in Guildford, a bustling university town in southeast England and home to the University of Surrey, while standing by a busy roadside, air pollution at stroller height – about 85 cm from the ground was measured. Using portable instruments, ultrafine particles (UFPs), PM2.5, PM10, and particle number concentrations (PNC) were monitored as part of a real-world exposure study conducted between August and late September 2018, during one of the UK’s hottest and driest summers on record.

Commuter traffic surged past with blaring horns, waves of diesel fumes, and the rhythmic stop-and-go of traffic signals. As I pushed a pram along a predefined school-run route, simulating a parent’s daily drop-off routine, I noticed others with young children passing by, unaware of the invisible pollutants in the air.

Our field measurements revealed that infants in prams are exposed to significantly higher levels of air pollution than the adults pushing them. In some cases, fine particle concentrations at the Pram level were up to 44 percent higher than adult breathing height. In double prams, the bottom seat, closer to the road, showed about 72 percent higher particle number concentrations (PNC) than the top.

Daily exposure varied as well: morning school runs saw 60 percent higher PNC than afternoons, driven by peak traffic and poor dispersion. Simple interventions such as pram covers offered partial protection, reducing exposure to fine and coarse particles by up to 43 percent. Microscopic analysis using SEM/EDS techniques identified brake and tyre wear particles as dominant sources at baby breathing height, highlighting the non-exhaust emissions as a key concern for young children’s respiratory health.

This quiet, everyday scene on a British roadside takes on a far more urgent meaning in cities like Delhi and Mumbai, where similar patterns unfold with much greater intensity. Each winter, Delhi faces a recurring public health emergency: dense smog, reduced visibility, and a sharp rise in respiratory illnesses. A major contributor is the seasonal burning of crop residue in Punjab, Haryana, and Uttar Pradesh, which releases thick plumes of particulate matter that spread across the Indo-Gangetic Basin.

This was where my research journey began — with a growing concern for those most vulnerable to air pollution in cities like Delhi and Mumbai: young children, the elderly, and people with respiratory conditions. Prams may be less common in India than in places like Guildford or London, but the risk remains the same. The most exposed are often the least protected. What started as a roadside study evolved into wider work on air filtration, urban design, and later, face mask efficacy and filter media testing at the Global Centre for Clean Air Research (GCARE), University of Surrey. One lesson became clear: clean air demands both personal protection and systemic change.

The common thread? Air—how we move it, filter it, and design for it. And in cities chasing net-zero targets, air is both our first challenge and our greatest opportunity.

Figure 1. Illustration of differential air pollution exposure near roadways: an adult pushing an infant in a pram along a roadside environment. The baby’s breathing height (~0.55–0.85 m) is within the most polluted air zone, where fine and ultrafine particle concentrations peak due to vehicle emissions and poor vertical dispersion – Adapted from Sharma & Kumar (2018), Environment International.

City-specific observations: urban hotspots as exposure amplifiers

The exposure disparity was starkly evident in cities like London, Guildford, and Delhi, where roadside walking routes near congested roads, bus stops, and signal intersections emerged as hotspots. A study involving a 2.1 km walking loop between the University of Surrey and a local school mirrored real-world school run exposure. It revealed ~62 percent diurnal variability in pollutant concentrations (PNC). It shows that morning runs were far more polluted than afternoons.

Mitigation Measures: Pram Covers, Clean Air Zones & Technology Integration

Technological and passive interventions offer some protection. The studies revealed that pram covers can reduce particle exposure by up to 43 percent, and the development of clean air zones around the breathing space of prams was emphasised as a key intervention. However, the authors argue that holistic mitigation—spanning tech, community, and policy—is vital.

Air pollution in bike trailers: A new dimension

Extending these concerns, research in 2022 examined pollution exposure in bike trailers, another mode of child transport, as shown in Figure 2. Children in bike trailers were found to experience 14 percent more PM2.5 than the accompanying adult cyclist. The trailer covers mitigated 50 percent of fine particle and 24 percent of black carbon exposure. These results are particularly relevant to cities promoting cycling infrastructure, such as Amsterdam, Berlin, and Bangalore.

Figure 2. Air pollution exposure differences between young children in bike trailers and adult cyclists, simulated by Sharma et al. (2022). Bars represent average concentrations (± standard deviation) of fine particulate matter (PM₂.₅) and black carbon (BC) measured at child and cyclist breathing heights across multiple school-run scenarios. PM 2.5 concentrations were up to 14 percent higher in the trailer, with BC showing up to 97 percent variability. Trailer covers reduced fine particles by up to 50 percent, underscoring the need for improved passive filtration and thermal shielding in child transport systems. Source: Sharma et al., 2022 – Journal of Hazardous Materials Advances.

Exploring urban vegetation’s role in air quality and health

In the race to green our cities, we often plant without planning. In another study (Environment International, 2019), we showed that poorly placed roadside trees could trap pollutants in urban street canyons, increasing human exposure rather than mitigating it.

This has major implications for eco-conscious building projects that pair green facades with sealed indoor environments. If we don’t understand the aerodynamics of vegetation, we risk creating buildings that are net-zero on paper, but health-negative in practice.

In another parallel research (Kumar et al., 2019), we examined the interplay between urban greenery, air pollution, and public health. Although green infrastructure (e.g., hedges, street trees, and green walls) can reduce downwind pollutant exposure, the deployment must be strategic to avoid trapping pollutants at street level. Cities like Chennai and Hyderabad have already begun integrating green buffers in traffic-dense zones as part of urban planning strategies.

In “Air pollution exposure assessment simulation of babies in a bike trailer and implication for mitigation measures”, babies in bike trailers were found to inhale up to 44 percent higher concentrations of fine particles compared to adults cycling ahead, with brake and tire wear particles dominating at stroller height. Together, these studies reinforce the urgent need for context-specific exposure mitigation, from mobile transport environments to everyday respiratory protection.

It mirrors a broader challenge in HVAC and filtration system design: how to maximise filter efficiency without compromising airflow or increasing energy demand. Just as dense face masks can impede breathing, high-MERV filters can overburden ventilation systems.

The study provides practical guidance for vulnerable groups such as caregivers, transit users, and those in polluted urban environments like London or Guildford, where cross-ventilation is promoted in public transport. The key takeaway is that effective filtration must balance material science, user comfort, and Smart airflow management.

Figure 3. Filtration-breathability trade-off across 11 types of face masks evaluated by Sharma et al. (2022). Circles represent mean filtration efficiency (± standard deviation) for submicron aerosols, plotted against quality factor (a measure of filtration performance) and estimated potential usage time based on breathing resistance. FFP3 respirators showed the highest filtration (up to 97 percent) but also greater breathing resistance, highlighting the balance between protection and comfort, relevant for both personal and HVAC system design. Source: Sharma et al., 2022 – Journal of Hazardous Materials.

Climate crisis and air pollution: India’s twin urban challenge

The climate crisis aggravates urban air pollution. India stands at a pivotal point. In our 2023 study published in Frontiers in Sustainable Cities, we examined India’s mounting exposure to the dual threats of climate-induced extreme weather and urban air pollution. The analysis revealed India ranked 7th globally for climate-related disasters, with 2,267 deaths and $66 billion in economic losses recorded in 2019 alone. With Delhi and Mumbai frequently topping global pollution charts, mitigation through nature-based solutions, urban planning, and emissions control remains critical.

Urban energy transitions and net-zero cities

To tackle air pollution and energy-related emissions in tandem, our 2025 review in Sustainable Futures outlines a comprehensive strategy for urban transformation. With cities responsible for nearly 70 percent of global greenhouse gas emissions, they must take a leading role in implementing smart urban energy transitions. This includes the integration of digital twin technologies for dynamic planning, widespread adoption of passive building design for energy efficiency, and ensuring equitable access to clean energy, which are key pillars of a sustainable, net-zero urban future (see Figure 4). Urban resilience strategies in megacities like Delhi, Mumbai, London, and Shenzhen must align with Sustainable Development Goals (SDG 11 & SDG 13) to ensure cleaner air and healthier populations.

Figure 4. Sustainability impact assessment framework for urban energy transitions in smart cities, as proposed in Sharma et al. (2025). The graphic outlines key strategies, including electrification, passive building design, digital twins, stakeholder collaboration, and life cycle assessments to support net-zero goals and urban energy resilience. Adopted from Sharma et al., 2025 – Sustainable Futures.

Filtering for the future and a call for multi-sectoral action

From pram and trailer-bound infants breathing disproportionately high levels of harmful particles, to the pandemic-era spotlight on clean air and personal protection, evidence is clear: urban air quality is a foundational public health issue. Air is the hidden infrastructure of the 21st-century city. It carries pollution, energy, and equity in equal measure. To meet our net-zero goals, we must design not just for kilowatts and carbon, but for human lungs at every height and every age. The research leaves no doubt—cities must prioritise the invisible health of their youngest residents, using scientific evidence as a guiding light for sustainable and just futures.

Solutions require an integrated approach—technological innovation, green design, behavioural change, and systemic urban reforms. Through interdisciplinary science and real-world implementation, we can shift HVAC from background utility to frontline resilience system—one that filters more than air. It filters inequity, inefficiency, and inaction.