Tazuko Morikawa

C2–C5 hydrocarbon concentrations in Central Osaka

Abstract Hourly measurements of nine C 2 –C 5 hydrocarbons (HCs) were made over a period of 15 months in the center of Osaka City, Japan. The measurements were made by using an automated system consisting of a combination of a gas preconcentrator and a gas chromatograph. The concentrations of all components were high in early winter and low in summer. The highest concentration was of C 2 H 4 , while C 3 H 6 showed the lowest concentration throughout the year, and was rarely detected in summer. There were small annual variations in the concentrations of C 4 –C 5 HC. The chemical reactions that affect HC concentrations were also examined. The seasonal C 2 H 4 /C 2 H 2 and C 3 H 6 /C 2 H 2 ratios were compared, taking into account that C 2 H 4 , C 2 H 2 , and C 3 H 6 are mainly from vehicles and the differences in their reactivities. Despite the high reactivity of C 2 H 4 , the C 2 H 4 /C 2 H 2 ratio was low in winter and high in summer, with the result that the C 2 H 4 consumption by chemical reaction seemed small in the center of the city. The behavior of C 3 H 6 /C 2 H 2 is opposite to that of C 2 H 4 /C 2 H 2 , illustrating the more reactive characteristics of C 3 H 6 . Regarding the effect of photochemical reactions, it was observed that HC’s levels drop as NO 2 /NO x increases. Though the slope does not show a direct proportionality to HC reactivity, reactivity of C 3 H 6 , which is the most reactive HC among the nine measured HCs, showed the largest declines. The ratio of C 4 –C 5 HC to the C 2 –C 5 HC rose with increase in ambient temperature, while the ratio of C 2 –C 5 HC to the nonmethane hydrocarbons decreased. This phenomenon was correlated with ambient temperature, indicating higher emissions of higher molecular weight HCs in summer.

Gaseous nitrous acid (HONO) and nitrogen oxides (NOx) emission from gasoline and diesel vehicles under real-world driving test cycles

ABSTRACT Reactive nitrogen species emission from the exhausts of gasoline and diesel vehicles, including nitrogen oxides (NOx) and nitrous acid (HONO), contributes as a significant source of photochemical oxidant precursors in the ambient air. Multiple laboratory and on-road exhaust measurements have been performed to estimate the NOx emission factors from various vehicles and their contribution to atmospheric pollution. Meanwhile, HONO emission from vehicle exhaust has been under-measured despite the fact that HONO can contribute up to 60% of the total hydroxyl budget during daytime and its formation pathway is not fully understood. A profound traffic-induced HONO to NOx ratio of 0.8%, established by Kurtenbach et al. since 2001, has been widely applied in various simulation studies and possibly linked to under-estimation of HONO mixing ratios and OH radical budget in the morning. The HONO/NOx ratios from direct traffic emission have become debatable when it lacks measurements for direct HONO emission from vehicles upon the fast-changing emission reduction technology. Several recent studies have reported updated values for this ratio. This study has reported the measurement of HONO and NOx emission as well as the estimation of exhaust-induced HONO/NOx ratios from gasoline and diesel vehicles using different chassis dynamometer tests under various real-world driving cycles. For the tested gasoline vehicle, which was equipped with three-way catalyst after-treatment device, HONO/NOx ratios ranged from 0 to 0.95 % with very low average HONO concentrations. For the tested diesel vehicle equipped with diesel particulate active reduction device, HONO/NOx ratios varied from 0.16 to 1.00 %. The HONO/NOx ratios in diesel exhaust were inversely proportional to the average speeds of the tested vehicles. Implications: Photolysis of HONO is a dominant source of morning OH radicals. Conventional traffic-induced HONO/NOx ratio of 0.8% has possibly linked to underestimation of the total HONO budget and consequently underestimation of OH radical budget. The recently reported HONO/NOx ratio of ~1.6% was used to stimulate HONO emission, which resulted in increased HONO concentrations during morning peak hours and its impact of 14% OH increment in the morning. However, the results were still lower than the measured concentrations. More studies should be conducted to establish an updated traffic-induced HONO/NOx ratio.

Contributions of Condensable Particulate Matter to Atmospheric Organic Aerosol over Japan

Because emission rates of particulate matter (PM) from stationary combustion sources have been measured without dilution or cooling in Japan, condensable PM has not been included in Japanese emission inventories. In this study, we modified an emission inventory to include condensable PM from stationary combustion sources based on the recent emission surveys using a dilution method. As a result, emission rates of organic aerosol (OA) increased by a factor of 7 over Japan. Stationary combustion sources in the industrial and energy sectors became the largest contributors to OA emissions over Japan in the revised estimates (filterable-plus-condensable PM), while road transport and biomass burning were the dominant OA sources in the previous estimate (filterable PM). These results indicate that condensable PM from large combustion sources makes critical contributions to total PM2.5 emissions. Simulated contributions of condensable PM from combustion sources to atmospheric OA drastically increased around urban and industrial areas, including the Kanto region, where OA concentrations increased by factors of 2.5-6.1. Consideration of condensable PM from stationary combustion sources improved model estimates of OA in winter but caused overestimation of OA concentrations in summer. Contributions of primary and secondary OA should be further evaluated by comparing with organic tracer measurements.

Formaldehyde and Methyl Nitrite Levels in a Garage During the Cold Start-Up of a Methanol Fueled Vehicle.

A three-dimensional computer simulation was performed to determine the formaldehyde (HCHO) and methyl nitrite (CH3ONO) levels inside a small garage during the cold start-up of a methanol fueled vehicle (MFV). The garage size was appropriate for one MFV. Two types of garage were considered in order to quantify the ventilation effect. The total amount of pollutants was independent of the ventilation until 70 s after engine start-up, because the pollutants remained concentrated directly behind the vehicle. After 180 s, the pollutant levels in the ventilated model were reduced to half that in the no-ventilated model. However, under such small garage condition, even with one ventilator, at a point 1 m behind the MFV and 1.5 m high, the HCHO concentration reached 9.2 ppm. To reduce the HCHO level to below 5 ppm, the HCHO peak concentration in the emission should be reduced to 0.5 times the present concentration. Although the harmful effects of CH3ONO have not yet been investigated in detail, they should be considered, particularly during cold start-up of MFV in a closed garage.