RESUMO
Volatile organic compounds (VOCs) are consumed by photochemical reactions during transport, leading to inaccuracies in estimating the local ozone (O3) formation mechanism and its subsequent strategy for O3 attainment. To comprehensively quantify the deviations in O3 formation mechanism by consumed VOCs (C-VOCs), a 5-month field campaign was conducted in a typical industrial city in Northern China over incorporating a 0-D box model (implemented with MCMv3.3.1). The averaged C-VOCs concentration was 6.8 ppbv during entire period, and Alkenes accounted for 62% dominantly. Without considering C-VOCs, the relative incremental reactivity (RIR) of anthropogenic VOCs (AVOC, overestimated by 68%-75%) and NOx (underestimated by 137%-527%) demonstrated deviations at multiple scenarios, and the RIR deviations for precursors in High-O3-periods (HOP) were lower than Low-O3-periods (LOP). The RIR deviations from individual species involved C-VOCs calculation did not impact the identification for the high-ranking-RIR AVOC species but non-negligible. Monthly comparisons showed that higher C-VOCs concentrations would lead to higher RIR deviations. The daily maximum of net Ox production rate (P(Ox)) and the regional transport Ox (Trans(Ox)) without C-VOCs were underestimated by 56%-194% and 81%-243%, respectively. After considering C-VOCs, the contribution of HO2+NO for Ox gross production (G(Ox)) decreased by 7% (LOP) and 7% (HOP), but OH + NO2 for Ox destruction (D(Ox)) decreased by 16% (LOP) and 23% (HOP), and alkenes + O3 increased for D(Ox) by 12% (LOP) and 22% (HOP). This implies that VOCs-NOx-O3 sensitivity was deviated between with/without C-VOCs, and severe O3 pollution rendered deviations in O3 formation, especially via NOx-driving chemistry. Based on RIR(NOx)/RIR(AVOC) with/without C-VOCs, the sensitivity regime shifted from VOCs-limited (-0.93) to transition (1.38) at LOP, and from VOCs-limited (0.19) to NOx-limited (3.79) at HOP. Our results reflected that the NOx limitation degree was underestimated without constraint C-VOCs, especially HOP, and provided implication to more precise O3 pollution control strategies.
Assuntos
Poluentes Atmosféricos , Cidades , Monitoramento Ambiental , Ozônio , Compostos Orgânicos Voláteis , Ozônio/análise , Ozônio/química , Compostos Orgânicos Voláteis/análise , China , Poluentes Atmosféricos/análise , Poluentes Atmosféricos/química , Monitoramento Ambiental/métodos , Processos FotoquímicosRESUMO
Black carbon (BC) significantly affects climate, environmental quality, and human health. This study utilised Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2), which can compensate for the shortcomings of ground BC monitoring in spatial-temporal distribution to study the pollution characteristics of BC and potential pollution sources in a typical industrial city (Xinxiang) with serious air pollution in northern China. The results showed that average daily ground observation and MERRA-2 concentration of BC of 7.33 µg m-3 and 9.52 µg m-3. The mean BC concentration derived from MERRA-2 reanalysis data was higher than ground measurement due to resolution limitations and pollution from the northern regions. The reliability of the MERRA-2 data was confirmed through correlation analysis. Consideration of the spatial distribution of BC from MERRA-2 and incorporating the potential source contribution function (PSCF), concentration-weighted trajectory (CWT), and emission inventory, other possible source areas and primary sources of BC in Xinxiang were investigated. The results indicated that implementing transportation and residential emission control measures in Henan Province and its surrounding provinces, such as Hebei Province, will effectively decrease the BC level in Xinxiang City. A passively smoked cigarettes model was used to evaluate the risk of BC exposure. The percentage of lung function decrement (PLFD) was the highest in school-age children, while the impact on lung cancer (LC) health risk was comparatively lower. Notably, the BC health risk in Xinxiang was lower than in most cities across Asia.
Assuntos
Poluentes Atmosféricos , Poluição do Ar , Criança , Humanos , Cidades , Poluentes Atmosféricos/análise , Estudos Retrospectivos , Reprodutibilidade dos Testes , Monitoramento Ambiental , China , Poluição do Ar/análise , Fuligem , Carbono/análise , Material Particulado/análiseRESUMO
To explore the formation mechanism of the ozone ï¼O3ï¼ and emission reduction strategy in a northwestern cityï¼ an extensive field campaign was conducted in summertime in 2021 in Yining Cityï¼ in which the 0-D box model incorporating the latest explicit chemical mechanism ï¼MCMv3.3.1ï¼ was applied for the first time to quantify the O3-NOx-VOCs sensitivity and formulate a precise O3 control strategy in this city. The results showed thatï¼ â the three indicators ï¼»i.e.ï¼ O3 formation potential ï¼OFPï¼ï¼ ·OH reaction rate ï¼k·OHï¼ï¼ and relative incremental reactivity ï¼RIRï¼ï¼½ jointly indicated that alkenesï¼ oxygenated volatile organic compounds ï¼OVOCsï¼ï¼ and aromatics were the highest contributors among anthropogenic volatile organic compounds ï¼AVOCï¼ to O3 formationï¼ and the contribution of biogenic volatile organic compounds ï¼BVOCï¼ also could not be ignored. Additionallyï¼ the results based on RIR calculation implied that that the acetaldehydeï¼ ethyleneï¼ and propylene were the most sensitive individual VOCs species in Yining City. â¡ The in-situ photochemical O3 variations were primarily influenced by the local photochemical production and export process horizontally to downwind areas or vertically to the upper layerï¼ and the reaction pathways of HO2·+ NO and ·OH + NO2 contributed the most to the gross Ox photochemical production ï¼60%ï¼ and photochemical destruction production ï¼53%ï¼ï¼ respectively. Henceï¼ the reduction in local emissions for O3 precursors was more essential to alleviate O3 pollution in this city. ⢠The outcome based on RIRï¼NOxï¼ / RIRï¼AVOCï¼ and EKMA jointly suggested that the photochemical regime in this city can be considered a transitional regime that was also nearly a VOCs-limited regime. Detailed mechanism modeling based on multiple scenarios further suggested that the NOx and VOCs synergic emission reduction strategies was helpful to alleviate O3 pollution. These results are useful to provide policy-related guidance for other cities facing similar O3 pollution in northwest China.
RESUMO
Quantifying the impact of carbonyl compounds (carbonyls) on ozone (O3) photochemical formation is crucial to formulating targeted O3 mitigation strategies. To investigate the emission source of ambient carbonyls and their integrated observational constraint on the impact of O3 formation chemistry, a field campaign was conducted in an industrial city (Zibo) of the North China Plain from August to September 2020. The site-to-site variations of OH reactivity for carbonyls were in accordance with the sequence of Beijiao (BJ, urban, 4.4 s-1) > Xindian (XD, suburban, 4.2 s-1) > Tianzhen (TZ, suburban, 1.6 s-1). A 0-D box model (MCMv3.3.1) was applied to assess the O3-precursor relationship influenced by measured carbonyls. It was found that without carbonyls constraint, the O3 photochemical production of the three sites was underestimated to varying degrees, and the biases of overestimating the VOC-limited degree were also identified through a sensitivity test to NOx emission changes, which may be associated with the reactivity of carbonyls. In addition, the results of the positive matrix factorization (PMF) model indicated that the main source of aldehydes and ketones was secondary formation and background (81.6% for aldehydes, 76.8% for ketones), followed by traffic emission (11.0% for aldehydes, 14.0% for ketones). Incorporated with the box model, we found that biogenic emission contributed the most to the O3 production at the three sites, followed by traffic emission as well as industry and solvent usage. Meanwhile, the relative incremental reactivity (RIR) values of O3 precursor groups from diverse VOC emission sources featured consistencies and differences at the three sites, which further highlights the importance of the synergetic mitigation of target O3 precursors at regional and local scales. This study will help to provide targeted policy-guiding O3 control strategies for other regions.
Assuntos
Poluentes Atmosféricos , Ozônio , Compostos Orgânicos Voláteis , Ozônio/análise , Poluentes Atmosféricos/análise , Compostos Orgânicos Voláteis/análise , Processos Fotoquímicos , Monitoramento Ambiental/métodos , China , Aldeídos , CetonasRESUMO
To investigate the characteristics and formation mechanism of ozone (O3) pollution in an industrial city, an extensive one-month field campaign focusing on O3 and its precursors (e.g., volatile organic compounds[VOC] and nitrogen oxides[NOx]) was conducted in Zibo City, a highly industrializd city in the North China Plain, in June 2021. The 0-D box model incorporating the latest explicit chemical mechanism (MCMv3.3.1) was applied using an observation dataset (e.g., VOC, NOx, HONO, and PAN) as model contraints to explore the optimal reduction strategy for O3 and its precursors. The results showed that â during high-O3 episodes, stagnant weather conditions with high temperature and solar radiation as well as low relative humidity were observed, and oxygenated VOCs and alkenes from anthropogenic VOCs contributed the most to the total ozone formation potential and OH reactivity (k·OH). â¡ The in-situ O3 variation was primarily affected by local photochemical production and export process horizontal to downwind areas or vertical to the upper layer. The reduction in local emissions was essential to alleviate O3 pollution in this region. ⢠During high-O3 episodes, high concentrations of ·OH (10×106 cm-3) and HO2· (14×108 cm-3) radical drove and generated a high O3 production rate (daytime peak value reached 36×10-9 h-1). The reaction pathways of HO2·+NO and ·OH+NO2 contributed the most to the in-situ gross Ox photochemical production (63%) and photochemical destruction (50%), respectively. ⣠Compared to those during low-O3 episodes, the photochemical regimes during high-O3 episodes were more inclined to be considered as the NOx-limited regime. Detailed mechanism modeling based on multiple scenarios further suggested that the synergic emission reduction strategy of NOx and VOC, while focusing on NOx emission alleviation, would be practical options for controlling local O3 pollutions. This method could also provide policy-related guidance for the precise O3 pollution prevention and control in other industrialized Chinese cities.
RESUMO
The significant role of traffic emissions mixed from various sources in urban air pollution has been widely recognized. However, the corresponding contributions to the roadside particle distribution are poorly understood due to the mixed impacts of various sources. Particle number concentrations of different sizes at the roadside in Nankai District of Tianjin were continuously monitored using a portable aerosol particle spectrometer during the morning rush hour (07:30-09:20) from Nov. 9, 2018 to Jan. 6, 2019. Characteristic and influencing factors of particle size distributions were discussed combined with temperature and relative humidity data, while potential sources of particles at the roadside were identified based on size distribution analysis. The results showed that the average total particle number concentrations were 502 cm-3, and the concentrations of the accumulation mode and coarse mode were 500 cm-3 and 2 cm-3, respectively. The distribution of number concentrations at the roadside was unimodal and primarily concentrated at 0.25-0.50 µm, with peak sizes at 0.28-0.30 µm. The same distribution trend of particle number concentration and difference in the concentration in the same segment size were observed at different periods. Vehicle activity level was the main influencing factor of road particulate matter concentration on different weekdays; the probability of the high value of road particulate matter concentration was reduced by a reasonable combination of the vehicle tail numbers. Temperature and relative humidity were both found to be positively correlated with the number concentration of particles. With the increase in temperature and relative humidity, the total and peak particle number concentration showed an overall upward trend. In addition, the peak particle size increased from 0.28-0.30 µm to 0.35-0.40 µm when relative humidity was higher than 80%. Three sources, including road dust, brake and tire wear, and the aging particles from vehicle exhaust, were identified using positive matrix factorization in this study. Road dust contributed 8.6% of the total number concentration, which mainly consisted of particles with sizes above 5.00 µm. Brake and tire wear contributed 2.8% of the total number concentration of particles with a size range of 0.80-4.00 µm. The aging particles from vehicle exhaust contributed the most (88.5%), with a peak at 0.25-0.65 µm. The sources of roadside particles were mainly related to vehicle activity, whereas temperature and relative humidity also affected the particle number size distribution.