Study of atmospheric CO2 and CH4 at Longfengshan WMO/GAW regional station： The variations, trends, influence of local sources/sinks, and transport

Atmospheric CO_2 and CH_4 have been continuously measured since 2009 at Longfengshan WMO/GAW station(LFS) in China. Variations of the mole fractions, influence of long-distance transport, effects of local sources/sinks and the characteristics of synoptic scale variations have been studied based on the records from 2009 to 2013. Both the CO_2 and CH_4 mole fractions display increasing trends in the last five years, with growth rates of 3.1±0.02 ppm yr.1 for CO_2 and 8±0.04 ppb yr.1(standard error, 1-σ)for CH_4. In summer, the regional CO_2 mole fractions are apparently lower than the Marine Boundary Layer reference, with the lowest value of.13.6±0.7 ppm in July, while the CH_4 values are higher than the MBL reference, with the maximum of 139±6 ppb.From 9 to 17(Local time, LT) in summer, the atmospheric CO_2 mole fractions at 10 m a.g.l. are always lower than at 80 m, with a mean difference of.1.1±0.2 ppm, indicating that the flask sampling approach deployed may underestimate the background mole fractions in summer. In winter, anthropogenic emissions dominate the regional CO_2 and CH_4 mole fractions. Cluster analysis of backward trajectories shows that atmospheric CO_2 and CH_4 at LFS are influenced by anthropogenic emissions from the southwest(Changchun and Jilin city) all year. The synoptic scale variations indicate that the northeastern China plain acts as an important source of atmospheric CO_2 and CH_4 in winter.

Influence of meteorological factors on open biomass burning at a background site in Northeast China

Biomass burning(BB)is a very important emission source that significantly adversely impacts regional air quality.BB produces a large number of primary organic aerosol(POA)and black carbon(BC).Besides,BB also provides many precursors for secondary organic aerosol(SOA)generation.In this work,the ratio of levoglucosan(LG)to organic carbon(OC)and the fire hotspots map was used to identify the open biomass burning(OBB)events,which occurred in two representative episodes,October 13 to November 30,2020,and April1 to April 30,2021.The ratio of organic aerosol(OA)to reconstructed PM_(2.5)concentration(PM_(2.5)^(*))increased with the increase of LG/OC.When LG/OC ratio is higher than 0.03,the highest OA/PM_(2.5)^(*)ratio can reach 80%,which means the contribution of OBB to OA is crucial.According to the ratio of LG to K^(+),LG to mannosan(MN)and the regional characteristics of Longfengshan,it can be determined that the crop residuals are the main fuel.The occurrence of OBB coincides with farmers’preferred choices,i.e.,burning biomass in“bright weather”.The“bright weather”refers to the meteorological conditions with high temperature,low humidity,and without rain.Meteorological factors indirectly affect regional biomass combustion pollution by influencing farmers’active choices.

Dramatic decline of observed atmospheric CO_(2) and CH_(4) during the COVID-19 lockdown over the Yangtze River Delta of China

The temporal variation of greenhouse gas concentrations in China during the COVID-19 lockdown in China is analyzed in this work using high resolution measurements of near surface ΔCO_(2),ΔCH_(4) andΔCO concentrations above the background conditions at Lin’an station(LAN),a regional background station in the Yangtze River Delta region.During the pre-lockdown observational period(IOP-1),bothΔCO_(2) andΔCH_(4) exhibited a significant increasing trend relative to the 2011-2019 climatological mean.The reduction ofΔCO_(2),ΔCH_(4) andΔCO during the lockdown observational period(IOP-2)(which also coincided with the Chinese New Year Holiday)reached up to 15.0 ppm,14.2 ppb and 146.8 ppb,respectively,and a reduction ofΔCO_(2)/ΔCO probably due to a dramatic reduction from industrial emissions.ΔCO_(2),ΔCH_(4) and ΔCO were observed to keep declining during the post-lockdown easing phase(IOP-3),which is the synthetic result of lower than normal CO_(2) emissions from rural regions around LAN coupled with strong uptake of the terrestrial ecosystem.Interestingly,the trend reversed to gradual increase for all species during the later easing phase(IOP-4),with ΔCO_(2)/ΔCO constantly increasing from IOP-2 to IOP-3 and finally IOP-4,consistent with recovery in industrial emissions associated with the staged resumption of economic activity.On average,ΔCO_(2) declined sharply throughout the days during IOP-2 but increased gradually throughout the days during IOP-4.The findings showcase the significant role of emission reduction in accounting for the dramatic changes in measured atmosphericΔCO_(2) and ΔCH_(4) associated with the COVID-19 lockdown and recovery.

RESEARCH ON SURFACE O_3 WITH METEOROLOGICAL CONDITIONS UNDER ATMOSPHERIC BACKGROUND CONDITIONS IN NORTHEAST CHINA

Surface O_3 concentration and its precursors have been observed at Longfengshan station, Heilongjiang Province for a period of one year from August 13,1994 to July 30,1995. Relationship between surface O_3 and the meteorological conditions during this period is analyzed in this study.Observation results show that diurnal variation of surface O_3 follows a pattern of double-peaks with amplitude of 27—28 ppb under fine days in summer and autumn.Although the diurnal variation is small(14 ppb),it is still detectable when it is overcast.Diurnal variation of O_3 is irregular under rainy days.Surface O_3 concentration rises when wind speed starts to increase at 0800 BT(Beijing Time)from 0 to 6 m s^(-1)in autumn,winter and summer.Relative high surface O_3 concentration is noticed frequently when S,SSW,SW and WSW wind are encountered at the station during all seasons.At 0800 BT and 1400 BT the surface O_3 concentration increases with the increase of global radiation accordingly during fine days in winter,spring and autumn.During fine days average peak of O_3 concentration in summer is 20 ppb higher than that in winter while the average peak of global radiation in summer is almost twice as high as that in winter.The average surface O_3 concentration under fine days in autumn at Longfengshan station is 14 ppb lower in comparison to the observation results from Lin'an station where Lin'an is at about the same longitude and lower latitude,with same environment,which is mainly caused by the difference of global radiation due to different latitudes in these two areas(difference of average peak global radiation about 100 W m^(-2)).