Underestimated benefits of NOx control in reducing SNA and O_(3)based on missing heterogeneous HONO sources

Substantial NOx emission mitigation is crucial for the synergistic reduction of particulate matter and ozone(O_(3))pollution in China.The traditional air quality model does not consider heterogeneous HONO chemistry,leading to uncertainties in estimating the benefits of NOx control.Previous studies have shown that the parameterization of heterogeneous HONO formation increases both the simulated value of sulfate–nitrate–ammonium(SNA)and that of O_(3),thus adding the heterogeneous reactions of HONO into air quality models inevitably leads to changes in the estimated benefits of NOx abatement.Here we investigated the changes in SNA and O_(3)concentrations from NOx emission reduction before and after adding heterogeneous HONO reactions in the Community Multi-Scale Air Quality(CMAQ)model.Including heterogeneous HONO reactions in the simulation improved the benefits of NOx reduction in terms of SNA control in winter.With 80%NOx reduction,the reduction in SNA increased from 36.9%without considering heterogeneous HONO reactions to 42.8%with heterogeneous HONO chemistry.The reduction in the maximum daily 8h average(MDA8)O_(3)in summer caused by NOx reduction increased slightly from 4.7%to 5.2%after adding heterogeneous HONO reactions.The results in this study highlight the enhanced effectiveness of NOx controls for the reduction of SNA and O_(3)after considering heterogeneous HONO formation in a complex chemical ambient,demonstrating the importance of NOx controls in reducing PM2.5 and O_(3)pollution in China.

Synergetic PM_(2.5) and O_(3) control strategy for the Yangtze River Delta,China

PM_(2.5)concentrations have dramatically reduced in key regions of China during the period 2013-2017,while O_(3)has increased.Hence there is an urgent demand to develop a synergetic regional PM_(2.5)and O_(3)control strategy.This study develops an emission-to-concentration response surface model and proposes a synergetic pathway for PM_(2.5)and O_(3)control in the Yangtze River Delta(YRD)based on the framework of the Air Benefit and Cost and Attainment Assessment System(ABaCAS).Results suggest that the regional emissions of NOx,SO_(2),NH3,VOCs(volatile organic compounds)and primary PM_(2.5)should be reduced by 18%,23%,14%,17%and 33%compared with 2017 to achieve 25%and 5% decreases of PM_(2.5)and O_(3)in 2025,and that the emission reduction ratios will need to be 50%,26%,28%,28% and 55%to attain the National Ambient Air Quality Standard.To effectively reduce the O_(3) pollution in the central and eastern YRD,VOCs controls need to be strengthened to reduce O_(3)by 5%,and then NOx reduction should be accelerated for air quality attainment.Meanwhile,control of primary PM_(2.5)emissions shall be prioritized to address the severe PM_(2.5)pollution in the northern YRD.For most cities in the YRD,the VOCs emission reduction ratio should be higher than that for NOx in Spring and Autumn.NOx control should be increased in summer rather than winter when a strong VOC-limited regime occurs.Besides,regarding the emission control of industrial processes,on-road vehicle and residential sources shall be prioritized and the joint control area should be enlarged to include Shandong,Jiangxi and Hubei Province for effective O_(3)control.

Understand the local and regional contributions on air pollution from the view of human health impacts

The source-receptor matrix of PM_(2.5)concentration from local and regional sources in the Beijing-Tianjin-Hebei(BTH)and surrounding provinces has been created in previous studies.However,because the spatial distribution of concentration does not necessarily match with that of the population,such concentration-based source-receptor matrix may not fully reflect the importance of pollutant control effectiveness in reducing the PM_(2.5)-related health impacts.To demonstrate that,we study the source-receptor matrix of the PM_(2.5)-related deaths instead,with inclusion of the spatial correlations between the concentrations and the population.The advanced source apportionment numerical model combined with the integrated exposure-response functions is used for BTH and surrounding regions in 2017.We observed that the relative contribution to PM_(2.5)-related deaths of local emissions was 0.75%to 20.77%larger than that of PM_(2.5)concentrations.Such results address the importance of local emissions control for reducing health impacts of PM_(2.5)particularly for local residents.Contribution of regional transport to PM_(2.5)-related deaths in rural area was 22%larger than that in urban area due to the spatial pattern of regional transport which was more related to the rural population.This resulted in an environmental inequality in the sense that people staying in rural area with access to less educational resources are subjected to higher impacts from regional transport as compared with their more resourceful and knowledgeable urban compatriots.An unexpected benefit from the multi-regional joint controls is suggested for its effectiveness in reducing the regional transport of PM_(2.5)pollution thus mitigating the associated environmental inequality.