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Due to increased concerns regarding air pollutants emitted from shipping, feasible technology for the surveillance of these pollutants is in high demand. Here, we present shore-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements of SO2 and NO2 emitted from ships under different traffic conditions in China's ship emission control areas (ECAs) in Shanghai and Shenzhen, China. Three typical measurement sites were selected in these two regions to represent the following emission scenarios: ships docked at berth, ships navigating in an inland waterway and inbound/outbound ships in a deep-water port. Using 2-D scanning, the observations show that SO2 and NO2 hot spots can be quickly and easily located from multiple berths. Although MAX-DOAS measurements can not distinguish plumes from specific ships in the busy shipping lanes of the inland waterway area, they certify that variations in the SO2 and NO2 levels are mainly impacted by the ship traffic density and the atmospheric dispersion conditions. In the open water area, which has a lower vessel density, MAX-DOAS measurements can capture the pulse signal of ship-emitted SO2 and NO2 very well; they can also characterize the peak's altitude and the insistent duration of the individual ship plumes. Combined with the ship activity data, information on the rated power of the engine and the fuel sulfur content, it was found that the SO2/NO2 ratio in a single plume is usually low (< 1.5) for inbound vessels due to the usage of the auxiliary engine, which has less power and uses "clean" fuel with a low sulfur content. Thus, an unexpectedly high SO2/NO2 ratio implies the use of fuel with a sulfur content exceeding the regulation limits. Therefore, the observed SO2/NO2 ratio in the plume of a single ship can be used as an index to indicate compliance (or noncompliance) with respect to the fuel sulfur content, and the suspicious ship can then be flagged for further enforcement. Combining the ship emissions estimated by actual operation parameters and the logical sulfur content, shore-based MAX-DOAS measurements will provide a fast and more accurate way to surveil ship emissions. [ABSTRACT FROM AUTHOR]

With the increasing concerns on summertime atmospheric photochemical pollution, the diagnosis and prevention of ozone pollution have been paid close attention. Both formaldehyde (HCHO) and glyoxal (CHOCHO) are ubiquitous oxidation intermediates of volatile organic compounds (VOCs). The ratio of glyoxal to formaldehyde (R GF) is used as a metric for VOCs emission sources. In this study, the mixing ratios of HCHO and CHOCHO have been measured by the active differential optical absorption spectroscopy (DOAS) method in the urban area of Shanghai during summertime in 2018, as well as other trace gases. The average levels of HCHO and CHOCHO are 3.31 ± 1.43 ppbv and 0.164 ± 0.073 ppbv, respectively. The similar diurnal patterns and high correlation between HCHO, CHOCHO and ozone levels implied that daytime photochemical processes are the dominant formation pathway for these trace gases. We find that with increased NO x levels, HCHO shows higher ozone formation potential relative to glyoxal. The R GF ratio increases with temperature and decreases with NO 2 levels. By investigating the coupling of typical VOCs species such as acetylene, toluene and isoprene with HCHO and CHOCHO, R GF is found to be strongly impacted by the ambient VOCs profiles, suggesting that R GF should be used with caution when linking it to a given VOC precursor source. Finally, the R GF variations with ozone pollution episodes and weather processes are also discussed. • Ambient HCHO and CHOCHO were observed by active DOAS technique. • HCHO and CHOCHO show the dominant pathway of photochemical formation during daytime. • With increased NOx levels, ozone formation potential of HCHO higher than CHOCHO. • CHOCHO to HCHO Ratio (R GF) increases with temperature and decreases with NO 2 levels. • R GF is strongly impacted by the VOCs profiles and should be used with caution. [ABSTRACT FROM AUTHOR]

Nitrous acid (HONO) is the primary source of hydroxyl radical (OH) during daytime and significantly contribute to the formation of secondary organic compounds (SOA) and atmospheric oxidizing capacity. One month simultaneous observations at ship channel site (SCS) and background site (BGS) in Shanghai, China were conducted to aim at estimating the HONO concentration from ship direct emission and analyzing the nocturnal budget of HONO during non-clean period in SCS. The HONO average concentrations at both BGS and SCS during non-clean period were 0.37 ± 0.42 ppbv and 0.91 ± 0.78 ppbv, respectively. The diurnal variation of HONO from ship direct emission presented a double-peak trend with a maximum value 0.38 ± 0.18 ppbv at 07:00 in the morning. The proportion of HONO emission from ships was in a range of 43%~74% in the daytime, while, the proportions were 42%~63% and 14%~28% at night in clean and non-clean periods, respectively. HONO nocturnal conversion frequencies from NO 2 were 0.29%/h at both sites in non-clean period, during which the deposition velocities of HONO were 0.21–1.4 cm/s and 0.34–1.4 cm/s at BGS and SCS, respectively. • HONO emission from ships is identified and measured by long-path DOAS. • Difficult-calculate and unknown HONO source substituted by background site observation. • Proportion of ship direct HONO emission was estimated on different cases. • The NO 2 -to-HONO conversion frequencies on ship channel site and background site were equal. [ABSTRACT FROM AUTHOR]

To investigate on the daytime OH and its implication to fine particle, the long-path differential optical absorption spectroscopy (LP-DOAS) system was employed to observe the main OH precursors of O 3 , HCHO and HONO, as well as NO 2 and NO 3 radical from April to August 2013 over Shanghai, China. The main OH production paths from HONO, HCHO and O 3 were estimated to be occupied around 57.6%, 30.5% and 11.9% during daytime. The daytime OH radical concentration under steady-state was averaged at 1.02 × 10 7 molec cm −3 , which was significantly impacted by the photolytic processes. The relationship between photolysis frequency j(O 1 D) and OH radical suggests that heavy fine particle loads can make the photolytic reactions less efficiently and decrease the OH production and concentration. Utilizing CO as the indicator, the part of PM 2.5 mass related to primary emitted sources was found less impacted by the OH levels. The contribution of secondary organic aerosol with metrics of O 3 was enhanced with the increases of the OH levels, while secondary inorganic part of PM 2.5 was favor of the condition that smaller OH concentrations that 5 × 10 5 –5 × 10 6 molec cm −3 . Meantime, a simplified multivariate model was employed to evaluate the influences of OH levels on different parts of fine particles related to different emission and sources. Normalized by solar radiation, this part of OH unrelated to radiation was found to be inversely related to the PM 2.5 , which indicates the self-cleansing capability of the atmosphere. [ABSTRACT FROM AUTHOR]