L.-W. A. Chen

Black and Organic Carbon Emission Inventories: Review and Application to California

Abstract Particulate black or elemental carbon (EC) (black carbon [BC]) and organic carbon (OC) affect climate, visibility, and human health. Several “top-down” and “bottom-up” global emission inventories for these components have compiled country-wide emission factors, source profiles, and activity levels that do not necessarily reflect local conditions. Recent estimates of global BC and OC emissions range from 8 to 24 and 33 to 62 Tg (1012 g) per year, respectively. U.S. BC emissions account for 5.6% of the global total emissions. Uncertainties in global BC emission estimates are a factor of 2 or more. The U.S. National Emissions Inventory is well documented, but its major source categories are not easily related to EC- and OC-emitting source subcategories. California’s bottom-up emission inventory is easily accessible at many levels of detail and provides an example of how sources can be regrouped for speciated emission rates. PM2.5 (particulate matter with aerodynamic diameters < 2.5 µm) emissions from these categories are associated with EC and OC source profiles to generate California’s speciated emissions. A BC inventory for California of 38,731 t/yr was comparable to the 33,281 t/yr estimated from a bottom-up global BC inventory. However, further examination showed substantial differences among subcategories, with the global inventory BC from fossil fuel combustion at two-thirds that from the California inventory and the remainder attributed to biomass burning. Major discrepancies were found for directly emitted OC, with the global inventory estimating more than twice that of the California inventory. Most of the discrepancy was due to differences in open biomass burning (wildfires and agricultural waste) for which carbon emissions are highly variable. BC and OC emissions are sensitive to the availability and variability of existing source profiles, and profiles more specific to fuels and operating conditions are needed to increase emission accuracy.

Exposure to PM2.5 and PAHs from the Tong Liang, China Epidemiological Study

Chemically speciated PM2.5 and particle-bound polycyclic aromatic hydrocarbon (PAH) measurements were made at three sites near urban Tong Liang, Chongqing, a Chinese inland city where coal combustion is used for electricity generation and residential purposes outside of the central city. Ambient sampling was based on 72-hr averages between 3/2/2002 and 2/26/2003. Elevated PM2.5 and PAH concentrations were observed at all three sites, with the highest concentrations found in winter and the lowest in summer. This reflects a coupling effect of source variability and meteorological conditions. The PM2.5 mass estimated from sulfate, nitrate, ammonium, organics, elemental carbon, crustal material, and salt corresponded with the annual average gravimetric mass within ±10%. Carbonaceous aerosol was the dominant species, while positive correlations between organic carbon and trace elements (e.g., As, Se, Br, Pb, and Zn) were consistent with coal-burning and motor vehicle contributions. Ambient particle-bound PAHs of molecular weight 168–266 were enriched by 1.5 to 3.5 times during the coal-fired power plant operational period. However, further investigation is needed to determine the relative contribution from residential and utility coal combustion and vehicular activities.

Overview of Real-World Emission Characterization Methods

Abstract Real-world emissions do not necessarily correspond with those derived from certification tests, owing to changes in equipment, fuels, and operating cycles. Therefore, emission rates from sources that affect ambient air quality are needed to drive air quality models and to provide accountability for air quality management strategies. Since the early 1960s, source characterization methods have been established that quantify emission rates to certify sources and determine their compliance over time. However, these certification and compliance methods have not been adapted to changes in emission processes and controls nor have they incorporated advances in measurement technology. This results in source tests that are incompatible with each other and with ambient measurement methods. Source characterization methods need to be improved to better represent real-world hardware, operating conditions, and feedstocks and to obtain more information at lower costs. Hot-ducted exhaust can be cooled to ambient temperatures prior to measurement to better approximate emissions as they appear in the atmosphere. Engine exhaust can be characterized in situ with portable monitoring systems. A portable wind tunnel can characterize fugitive dust threshold suspension velocities, reservoir sizes, particle size distributions, and chemical profiles.

Hong Kong Vehicle Emission Changes from 2003 to 2015 in the Shing Mun Tunnel

ABSTRACT This study characterized motor vehicle emission rates and compositions in Hong Kongs Shing Mun tunnel (SMT) during 2015 and compared them to similar measurements from the same tunnel in 2003. Average PM2.5 concentrations in the SMT decreased by ∼70% from 229.1 ± 22.1 µg/m3 in 2003 to 74.2 ± 2.1 µg/m3 in 2015. Both PM2.5 and sulfur dioxide (SO2) emission factors (EFD) were reduced by ∼80% and total non-methane (NMHC) hydrocarbons EFD were reduced by 44%. These reductions are consistent with long-term trends of roadside ambient concentrations and emission inventory estimates, indicating the effectiveness of emission control measures. EFD changes between 2003 and 2015 were not statistically significant for carbon monoxide (CO), ammonia (NH3), and nitrogen oxides (NOx). Tunnel nitrogen dioxide (NO2) concentrations and NO2/NOx volume ratios increased, indicating an increased NO2 fraction in the primary vehicle exhaust emissions. Elemental carbon (EC) and organic matter (OM) were the most abundant PM2.5 constituents, with EC and OM, respectively, contributing to 51 and 31% of PM2.5 in 2003, and 35 and 28% of PM2.5 in 2015. Average EC and OM EFD decreased by ∼80% from 2003 to 2015. The sulfate EFD decreased to a lesser degree (55%) and its contribution to PM2.5 increased from 10% in 2003 to 18% in 2015, due to influences from ambient background sulfate concentrations. The contribution of geological materials to PM2.5 increased from 2% in 2003 to 5% in 2015, signifying the importance of non-tailpipe emissions.