Gen Zhang

Concrete supply chain transportation is a concentrated but often hidden source of urban freight emissions in megacities. This study develops a segment-resolved bottom-up NOx emission inventory for Beijing’s concrete supply chain in 2024, covering aggregate, cement, rail-to-truck transfer, and ready-mixed concrete delivery activities, and couples it with a logistic technology-diffusion model and Monte Carlo uncertainty analysis to evaluate clean-transition pathways through 2035. Results show that NOx emissions from concrete supply chain transportation reached 4994.7 tonnes in 2024, equivalent to approximately 20.0% of Beijing’s total on-road vehicle NOx emissions. Emissions were highly concentrated in aggregate inter-regional road transportation (58.5%) and concrete local road transportation (31.9%), while China V heavy-duty diesel trucks were the dominant fleet contributor. Under business as usual (BAU), natural fleet turnover reduces NOx emissions by 49.9% by 2035. Road-to-rail modal shift (RTR) and vehicle electrification transition (VET) achieve larger reductions of 60.5% and 76.3%, respectively, and the combined policy (CP) scenario reaches an 87.8% reduction. Uncertainty analysis confirms the robust ranking of policy effectiveness despite variability in activity levels, emission factors, and technology adoption. These findings show that deep mitigation requires matching policies to logistics functions: rail substitution for long-distance bulk haulage, electrification for short-haul urban delivery, and clean feeder transport to avoid end point pollution transfer.

Formaldehyde (HCHO) is an important precursor to atmospheric radicals, yet its complex sources remain poorly constrained. This study quantifies primary formaldehyde emissions from residential coal combustion and biomass burning using wintertime observations at a rural site in North China. A bimodal diurnal pattern of formaldehyde was observed, with morning peaks linked to coal combustion and afternoon peaks associated with biomass burning, supported by its strong correlations with combustion tracers (e.g., CO and SO₂) and intermittent household heating behaviors. Primary emission ratios of formaldehyde were determined to be 0.41 ppbv ppbv^-1 relative to SO₂ for coal combustion and 0.004 ppbv ppbv^-1 relative to CO for biomass burning based on the minimum R squared method. While the field-derived emission ratio for biomass burning agrees with current inventories, the ratio for coal combustion exceeds inventory estimates by up to an order of magnitude, indicating a significant underestimation of formaldehyde emissions from residential coal combustion. This underestimation is further corroborated by direct measurements from household coal combustion experiments and independent observations at another rural site. Chemical box model simulations show that observed formaldehyde significantly influences atmospheric chemistry, contributing 28, 16, and 21% to modeled HO₂, RO₂, and OH concentrations, respectively; 22% to ozone production rate; and 0.64 μg m^-3 to particulate hydroxymethanesulfonate concentrations. These findings highlight the critical role of formaldehyde in winter atmospheric chemistry and the urgent need to revise its emission estimates from residential coal combustion in the current inventory.

Nitrous acid (HONO) governs wintertime hydroxyl radical (OH) production, critically linking radical cycling, tropospheric oxidative capacity, and air pollution. During a mid‐latitude snowfall event, rapid HONO enrichment was observed alongside concurrent depletion of other pollutants. This unexpected phenomenon is attributed to heterogeneous reactions on fresh snow's high surface area, an interpretation supported by HONO budget parameterization. In contrast, aged snowpack exhibited negligible production potential, contradicting prior snowpack source identifications. This divergence arises from snow aging processes that reduce surface area and alter chemical reactivity. These findings reveal previously unrecognized meteorology‐chemistry interactions, underscoring further investigation into these complex processes.

Clouds and fogs, consisting of tiny water droplets formed by the condensation of water in supersaturated air, are vital in atmospheric chemistry, as they facilitate multiphase reactions. While measuring high-altitude cloud is challenging, fog as ground-level clouds offer a unique opportunity for direct observation. In this study, we explored radiation fogs in the North China Plain using an advanced aerosol-fog sampling system to measure the chemical and physical properties of both inactivated interstitial aerosols and activated fog droplet residues. Our findings revealed that efficient nitrate formation primarily occurred on fog interstitial aerosols rather than within fog droplets, with observed fog interstitial aerosol nitrate net production rates reaching up to 3.6 μg m^-3 h^-1. Box model simulations identified the hydrolysis of NO₂ and N₂O₅ as key pathways for nitrate formation. NO₂ hydrolysis was often overlooked in previous studies, contributing 40-79 and 57-76% to total nitrate production during nighttime and daytime fog periods. This oversight suggests that substantial nitrate formation through hydrolysis reactions involving interstitial aerosols may have been neglected. Our results highlight the need for further research into the chemistry of cloud and fog interstitial aerosols and their inclusion in atmospheric chemistry models.

The growth of newly formed particles through new particle formation (NPF) contributes a significant fraction to the cloud condensation nuclei, yet the driving mechanisms remain unclear, especially for polluted environments. To investigate the potential species contributing for nanoparticle growth in environments with significant anthropogenic influences, we measured the hygroscopicity of newly formed particles at 20–40 nm at a rural observational site in the North China Plain during winter 2018. Our results demonstrate that these particles were not very hygroscopic, with the mean hygroscopicity parameter κ of 0.13 ± 0.09. Clear differences in the inferred κ of the growing material responsible for the growth were observed among different events, indicating that even at the same region, the compounds driving particle growth may not be identical. This may be synergistically influenced by the NPF precursors, oxidants and meteorological conditions, suggesting complex mechanisms might co‐exist behind nanoparticle growth in polluted environments.

Solar radiation triggers atmospheric nitrous acid (HONO) photolysis, producing OH radicals, thereby accelerating photochemical reactions, leading to severe secondary pollution formation. Missing daytime sources were detected in the extensive HONO budget studies carried out in the past. In the rural North China Plain, some studies attributed those to soil emissions and more recent studies to dew evaporation. To investigate the contributions of these two processes to HONO temporal variations and unknown production rates in rural areas, HONO and related field observations obtained at the Gucheng Agricultural and Ecological Meteorological Station during spring and autumn were thoroughly analyzed. Morning peaks in HONO frequently occurred simultaneously with those of ammonia (NH₃) and water vapor both during spring and autumn, which were mostly caused by dew and guttation water evaporation. In spring, the unknown HONO production rate revealed pronounced afternoon peaks exceeding those in the morning. In autumn, however, the afternoon peak was barely detectable compared to the morning peak. The unknown afternoon HONO production rates were attributed to soil emissions due to their good relationship to soil temperatures, while NH₃ soil emissions were not as distinctive as dew emissions. Overall, the relative daytime contribution of dew emissions was higher during autumn, while soil emissions dominated during spring. Nevertheless, dew emission remained the most dominant contributor to morning time HONO emissions in both seasons, thus being responsible for the initiation of daytime OH radical formation and activation of photochemical reactions, while soil emissions further maintained HONO and associated OH radial formation rates at a high level, especially during spring. Future studies need to thoroughly investigate the influencing factors of dew and soil emissions and establish their relationship to HONO emission rates, form reasonable parameterizations for regional and global models, and improve current underestimations in modeled atmospheric oxidation capacity.