Observationally constrained modeling of atmospheric oxidation capacity and photochemical reactivity in Shanghai, China

16 pags., 8 figs., 2 tabs.An observation-based model coupled to the Master Chemical Mechanism (V3.3.1) and constrained by a full suite of observations was developed to study atmospheric oxidation capacity (AOC), OH reactivity, OH chain length and HOx (=OHCHO) budget for three different ozone (O3) concentration levels in Shanghai, China. Five months of observations from 1 May to 30 September 2018 showed that the air quality level is lightly polluted or worse (Ambient Air Quality Index, AQI, of > 100) for 12 d, of which ozone is the primary pollutant for 10 d, indicating ozone pollution was the main air quality challenge in Shanghai during summer of 2018. The levels of ozone and its precursors, as well as meteorological parameters, revealed the significant differences among different ozone levels, indicating that the high level of precursors is the precondition of ozone pollution, and strong radiation is an essential driving force. By increasing the input JNO value by 40 %, the simulated O3 level increased by 30 %-40 % correspondingly under the same level of precursors. The simulation results show that AOC, dominated by reactions involving OH radicals during the daytime, has a positive correlation with ozone levels. The reactions with non-methane volatile organic compounds (NMVOCs; 30 %-36 %), carbon monoxide (CO; 26 %-31 %) and nitrogen dioxide (NO; 21 %-29 %) dominated the OH reactivity under different ozone levels in Shanghai. Among the NMVOCs, alkenes and oxygenated VOCs (OVOCs) played a key role in OH reactivity, defined as the inverse of the OH lifetime. A longer OH chain length was found in clean conditions primarily due to low NO in the atmosphere. The high level of radical precursors (e.g., O3, HONO and OVOCs) promotes the production and cycling of HOx, and the daytime HOx primary source shifted from HONO photolysis in the morning to O3 photolysis in the afternoon. For the sinks of radicals, the reaction with NO dominated radical termination during the morning rush hour, while the reactions of radical-radical also contributed to the sinks of HOx in the afternoon. Furthermore, the top four species contributing to ozone formation potential (OFP) were HCHO, toluene, ethylene and m/p-xylene. The concentration ratio (∼ 23 %) of these four species to total NMVOCs is not proportional to their contribution (∼ 55 %) to OFP, implying that controlling key VOC species emission is more effective than limiting the total concentration of VOC in preventing and controlling ozone pollution.This research has been supported by the National Key Research and Development Program of China (grant nos. 2017YFC0210002, 2016YFC0200401 and 2018YFC0213801), the National Natural Science Foundation of China (grant nos. 41775113, 21777026 and 21607104), the Shanghai Pujiang Talent Program (grant no. 17PJC015), and the Shanghai Rising-Star Program (grant no. 18QA1403600). This work was also funded by The Program for Professor of Special Appointment (Eastern Scholar) at Shanghai Institutions of Higher Learning and Shanghai Thousand Talents Program

Long-term trends and drivers of aerosol pH in eastern China

Aerosol acidity plays a key role in regulating the chemistry and toxicity of atmospheric aerosol particles. The trend of aerosol pH and its drivers is crucial in understanding the multiphase formation pathways of aerosols. Here, we reported the first trend analysis of aerosol pH from 2011 to 2019 in eastern China, calculated with the ISORROPIA model based on observed gas and aerosol compositions. The implementation of the Air Pollution Prevention and Control Action Plan led to −35.8 %, −37.6 %, −9.6 %, −81.0 % and 1.2 % changes of PM2.5, SO42-, NHx, non-volatile cations (NVCs) and NO3- in the Yangtze River Delta (YRD) region during this period. Different from the drastic changes of aerosol compositions due to the implementation of the Air Pollution Prevention and Control Action Plan, aerosol pH showed a minor change of −0.24 over the 9 years. Besides the multiphase buffer effect, the opposite effects from the changes of SO42- and non-volatile cations played key roles in determining this minor pH trend, contributing to a change of +0.38 and −0.35, respectively. Seasonal variations in aerosol pH were mainly driven by the temperature, while the diurnal variations were driven by both temperature and relative humidity. In the future, SO2, NOx and NH3 emissions are expected to be further reduced by 86.9 %, 74.9 % and 41.7 % in 2050 according to the best health effect pollution control scenario (SSP1-26-BHE). The corresponding aerosol pH in eastern China is estimated to increase by ∼0.19, resulting in 0.04 less NO3- and 0.12 less NH4+ partitioning ratios, which suggests that NH3 and NOx emission controls are effective in mitigating haze pollution in eastern China.</p

Emissions of volatile organic compounds (VOCs) from cooking and their speciation: A case study for Shanghai with implications for China

Cooking emission is one of sources for ambient volatile organic compounds (VOCs), which is deleterious to air quality, climate and human health. These emissions are especially of great interest in large cities of East and Southeast Asia. We conducted a case study in which VOC emissions from kitchen extraction stacks have been sampled in total 57 times in the Megacity Shanghai. To obtain representative data, we sampled VOC emissions from kitchens, including restaurants of seven common cuisine types, canteens, and family kitchens. VOC species profiles and their chemical reactivities have been determined. The results showed that 51.26% ± 23.87% of alkane and 24.33 ± 11.69% of oxygenated VOCs (O-VOCs) dominate the VOC cooking emissions. Yet, the VOCs with the largest ozone formation potential (OFP) and secondary organic aerosol potential (SOAP) were from the alkene and aromatic categories, accounting for 6.8–97.0% and 73.8–98.0%, respectively. Barbequing has the most potential of harming people's heath due to its significant higher emissions of acetaldehyde, hexanal, and acrolein. Methodologies for calculating VOC emission factors (EF) for restaurants that take into account VOCs emitted per person (EFperson), per kitchen stove (EFkitchen stove) and per hour (EFhour) are developed and discussed. Methodologies for deriving VOC emission inventories (S) from restaurants are further defined and discussed based on two categories: cuisine types (Stype) and restaurant scales (Sscale). The range of Stype and Sscale are 4124.33–7818.04 t/year and 1355.11–2402.21 t/year, respectively. We also found that Stype and Sscale for 100,000 people are 17.07–32.36 t/year and 5.61–9.95 t/year, respectively. Based on Environmental Kuznets Curve, the annual total amount of VOCs emissions from catering industry in different provinces in China was estimated, which was 5680.53 t/year, 6122.43 t/year, and 66,244.59 t/year for Shangdong and Guangdong provinces and whole China, respectively. Large and medium-scaled restaurants should be paid more attention with respect to regulation of VOCs

Intercomparison of Ambient Nitrous Acid Measurements in a Shanghai Urban Site

Nitrous acid (HONO) is the major source of OH radicals in polluted regions and plays a key role in the nitrogen cycle of the atmosphere. Therefore, accurate measurements of HONO in the atmosphere is important. Long Path Absorption Photometer (LOPAP) is a common and highly sensitive method used for ambient HONO measurements. Incoherent Broadband Cavity Enhanced Absorption Spectroscopy (IBBCEAS) is a recent alternative for the detection of HONO with high temporal and spatial resolutions, which has shown a detection limit of 0.76 ppbv at a sampling average of 180 s. In this study, LOPAP and IBBCEAS-HONO instruments were deployed in a Shanghai Urban Site (Shanghai Academy of Environmental Sciences) and simultaneously recorded the data from both instruments for a quantitative intercomparison of the measured atmospheric HONO for four days from 30 December 2017&ndash;2 January 2018. The HONO concentration measured by IBBCEAS and LOPAP were well matched. The campaign average concentrations measured by IBBCEAS and LOPAP were 1.28 and 1.20 ppbv, respectively. The intercomparison results demonstrated that both the IBBCEAS-HONO instrument and LOPAP-HONO instrument are suitable for ambient monitoring of HONO in a polluted urban environment

Intercomparison of Ambient Nitrous Acid Measurements in a Shanghai Urban Site

Nitrous acid (HONO) is the major source of OH radicals in polluted regions and plays a key role in the nitrogen cycle of the atmosphere. Therefore, accurate measurements of HONO in the atmosphere is important. Long Path Absorption Photometer (LOPAP) is a common and highly sensitive method used for ambient HONO measurements. Incoherent Broadband Cavity Enhanced Absorption Spectroscopy (IBBCEAS) is a recent alternative for the detection of HONO with high temporal and spatial resolutions, which has shown a detection limit of 0.76 ppbv at a sampling average of 180 s. In this study, LOPAP and IBBCEAS-HONO instruments were deployed in a Shanghai Urban Site (Shanghai Academy of Environmental Sciences) and simultaneously recorded the data from both instruments for a quantitative intercomparison of the measured atmospheric HONO for four days from 30 December 2017–2 January 2018. The HONO concentration measured by IBBCEAS and LOPAP were well matched. The campaign average concentrations measured by IBBCEAS and LOPAP were 1.28 and 1.20 ppbv, respectively. The intercomparison results demonstrated that both the IBBCEAS-HONO instrument and LOPAP-HONO instrument are suitable for ambient monitoring of HONO in a polluted urban environment

Intercomparison of NO3 under Humid Conditions with Open-Path and Extractive IBBCEAS in an Atmospheric Reaction Chamber

We report an open-path incoherent broadband cavity-enhanced absorption spectroscopy (OP-IBBCEAS) technique for in situ simultaneous optical monitoring of NO2, NO3, and H2O in a reaction chamber. The measurement precision values (1&sigma;) are 2.9 ppbv and 2.9 pptv for NO2 and NO3 in 2 s, respectively, and the measurement uncertainties are 6% for NO2 and 14% for NO3. Intercomparison of measured concentrations of NO2 and NO3 by open-path and extractive IBBCEAS was carried out in the SAES-ARC reaction chamber during the reaction of NO2 with O3. The measurement accuracy of OP-IBBCEAS is verified by an NO2 intercomparison and the NO3 transmission efficiency of the extractive IBBCEAS is determined by comparison against the in situ NO3 measurement. The relationship between H2O absorption cross section and its mixing ratio at 295 K and 1 atm was analysed. Due to the spectral resolution of IBBCEAS system, the strong and narrow absorption lines of H2O are unresolved and exhibit non-Beer&ndash;Lambert Law behaviour. Therefore, a correction method is used to obtain the effective absorption cross section for fitting the H2O structure. An inappropriate H2O absorption cross section can cause an overestimation of NO3 concentration of about 28% in a humid atmosphere (H2O = 1.8%). This spectroscopic correction provides an approach to obtain accurate NO3 concentrations for open-path optical configurations, for example in chamber experiments or field campaigns. The measurement precision values are improved by a factor of 3 to 4 after applying Kalam filtering, achieving sub-ppbv (0.8 ppbv) and sub-pptv (0.9 pptv) performance in 2 s for NO2 and NO3, respectively

Intercomparison of NO₃ under Humid Conditions with Open-Path and Extractive IBBCEAS in an Atmospheric Reaction Chamber

We report an open-path incoherent broadband cavity-enhanced absorption spectroscopy (OP-IBBCEAS) technique for in situ simultaneous optical monitoring of NO2, NO3, and H2O in a reaction chamber. The measurement precision values (1σ) are 2.9 ppbv and 2.9 pptv for NO2 and NO3 in 2 s, respectively, and the measurement uncertainties are 6% for NO2 and 14% for NO3. Intercomparison of measured concentrations of NO2 and NO3 by open-path and extractive IBBCEAS was carried out in the SAES-ARC reaction chamber during the reaction of NO2 with O3. The measurement accuracy of OP-IBBCEAS is verified by an NO2 intercomparison and the NO3 transmission efficiency of the extractive IBBCEAS is determined by comparison against the in situ NO3 measurement. The relationship between H2O absorption cross section and its mixing ratio at 295 K and 1 atm was analysed. Due to the spectral resolution of IBBCEAS system, the strong and narrow absorption lines of H2O are unresolved and exhibit non-Beer–Lambert Law behaviour. Therefore, a correction method is used to obtain the effective absorption cross section for fitting the H2O structure. An inappropriate H2O absorption cross section can cause an overestimation of NO3 concentration of about 28% in a humid atmosphere (H2O = 1.8%). This spectroscopic correction provides an approach to obtain accurate NO3 concentrations for open-path optical configurations, for example in chamber experiments or field campaigns. The measurement precision values are improved by a factor of 3 to 4 after applying Kalam filtering, achieving sub-ppbv (0.8 ppbv) and sub-pptv (0.9 pptv) performance in 2 s for NO2 and NO3, respectively